NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

High Ethanol Fuel Endurance:

A Study of the Effects of 

Running Gasoline with 15% 

Ethanol Concentration in 

Current Production Outboard 

Four-Stroke Engines and 

Conventional Two-Stroke 

Outboard Marine Engines 

June 16, 2010 – June 30, 2011

David Hilbert 

Mercury Marine

Fond du Lac, Wisconsin 

Subcontract Report

NREL/SR-5400-52909

October 2011 
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

High Ethanol Fuel Endurance:

A Study of the Effects of 

Running Gasoline with 15% 

Ethanol Concentration in 

Current Production Outboard 

Four-Stroke Engines and 

Conventional Two-Stroke 

Outboard Marine Engines

June 16, 2010 – June 30, 2011

David Hilbert 

Mercury Marine

Fond du Lac, Wisconsin 

NREL Technical Monitor: Keith Knoll 

Prepared under Subcontract No. NFM-0-40044-01

Subcontract Report

NREL/SR-5400-52909

October 2011
This publication was reproduced from the best available copy

submitted by the subcontractor and received no editorial review at NREL.

NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of 

any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately 

owned rights. Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, 

or favoring by the United States government or any agency thereof. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy

and its contractors, in paper, from:

U.S. Department of Energy

Office of Scientific and Technical Information

P.O. Box 62

Oak Ridge, TN 37831-0062

phone: 865.576.8401

fax: 865.576.5728

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from:

U.S. Department of Commerce

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

phone: 800.553.6847

fax: 703.605.6900

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/help/ordermethods.aspx

Cover Photos: (left to right) PIX 16416, PIX 17423, PIX 16560, PIX 17613, PIX 17436, PIX 17721

Printed on paper containing at least 50% wastepaper, including 10% post consumer waste.
Page 1 of 52

Mercury Marine Product Development and Engineering

High Ethanol Fuel Endurance 

A study of the effects of running gasoline with 15% 

ethanol concentration in current production outboard

four-stroke engines and conventional two-stroke

outboard marine engines.

Mercury Marine 

Marine Products and Services 

W6250 Pioneer Road 

P.O. Box 1939 

Fond du Lac, WI 54936-1939 USA 

Phone: 920-929-5000 

www.mercurymarine.com 

Author:

David Hilbert

 Thermodynamic Development Engineer 

Approved: 

 Timothy Reid 

Director: Engine Design and Development 
Page 2 of 52

Table of Contents

Acknowledgements: ................................................................................................................................................................... 4

Executive Summary .................................................................................................................................................................... 5

Objective:................................................................................................................................................................................. 5

Summary of Results:.............................................................................................................................................................. 5

9.9HP Carbureted Four-Stroke:......................................................................................................................................... 5

300HP Four-Stroke Supercharged Verado: ..................................................................................................................... 5

200HP EFI 2.5L Two-Stroke:.............................................................................................................................................. 6

4.3L V6 EFI Four-Stroke Catalyzed Sterndrive:............................................................................................................... 6

Conclusions and Recommendations: .................................................................................................................................. 6

Introduction ................................................................................................................................................................................. 7

Project Background:............................................................................................................................................................... 7

Summary of Marine Engine Considerations:....................................................................................................................... 7

Investigation Details ................................................................................................................................................................... 9

Statement of Problem:............................................................................................................................................................ 9

Procedure:........................................................................................................................................................................... 9

Test Engine Description: ................................................................................................................................................. 10

Test Fuel Description:...................................................................................................................................................... 11

Engine Testing Results............................................................................................................................................................. 13

9.9HP Four-Stroke: ............................................................................................................................................................... 13

Endurance Test Results................................................................................................................................................... 13

Emissions Testing Results.............................................................................................................................................. 13

Engine Performance Comparison................................................................................................................................... 18

End of Test Teardown and Inspection ........................................................................................................................... 22

Verado 300HP Supercharged Four-Stroke:........................................................................................................................ 25

Endurance Test Results................................................................................................................................................... 25

Emissions Testing Results.............................................................................................................................................. 33

Engine Performance Comparison................................................................................................................................... 37

End of Test Teardown and Inspection ........................................................................................................................... 40

200 EFI Two-Stroke:.............................................................................................................................................................. 42

Endurance Test Results................................................................................................................................................... 42

Emissions Testing Results.............................................................................................................................................. 43

Engine Performance Comparison................................................................................................................................... 45

End of Test Teardown and Inspection ........................................................................................................................... 47

Additional Testing................................................................................................................................................................. 48

4.3L V6 Catalyzed Sterndrive Emissions Comparison ................................................................................................. 48

Final Summary........................................................................................................................................................................... 50

Summary of Results:............................................................................................................................................................ 50

Recommendations:............................................................................................................................................................... 51

References:............................................................................................................................................................................ 52

List of Tables

Table 1: Test Engine Specifications............................................................................................................................... 11

Table 2: Fuel Analysis Results....................................................................................................................................... 11

Table 3: Hardness Measurements on Various 9.9HP Four-Stroke Engine Components.............................................. 25

Table 4: Verado Exhaust Valve Hardness Measurement Summary ............................................................................. 28

Table 5: Hardness Measurements on Various 200HP EFI Two-Stroke Engine Components....................................... 47

Table 6: Fuel Flow Comparison on 4.3L V6 Catalyst Sterndrive, EEE vs. E15............................................................. 49
Page 3 of 52

List of Figures

Figure 1: Power to Weight Comparison, Scatter Band Data Provided by FEV (FEV Motorentechnik GmbH)1.......... 8

Figure 2: Example Load Curve Comparison (Automotive data – source 2, boat load data – internal Mercury source)

..................................................................................................................................................................................... 9

Figure 3: Distillation Curves of Test Fuels ................................................................................................................. 13

Figure 4: 9.9HP Four-Stroke HC+NOx Emissions Results Summary ....................................................................... 14

Figure 5: 9.9HP Four-Stroke HC Emissions Results Summary ................................................................................ 15

Figure 6: 9.9HP Four-Stroke NOx Emissions Results Summary .............................................................................. 15

Figure 7: 9.9HP Four-Stroke CO Emissions Results Summary ................................................................................ 16

Figures 8 & 9: Change in Equivalence Ratio vs. Endurance Time-EEE Fuel on E0 engine and E15 Engine.......... 16

Figure 10: Change in Equivalence Ratio vs. Endurance Time-E15 Fuel on E15 Engine ......................................... 17

Figures 11, 12, and 13: Hydrocarbon Emissions Outputs for Each Emissions Test, E15 Engine on E15 Fuel........ 18

Figure 14: E0 Engine Power and Torque Output at Endurance Check Intervals...................................................... 19

Figure 15: E15 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 Fuel.............................. 20

Figure 16: E15 Engine Power and Torque Output at Endurance Check Intervals-E15 Fuel .................................... 20

Figure 17: E15 Engine Power and Torque Output, Zero Hour Check-E0-EEE Fuel vs. E15 Fuel............................ 21

Figure 18: E15 Engine-Exhaust Gas Temperature Comparison, Zero Hour Check-E0-EEE Fuel vs. E15 Fuel...... 22

Figure 19: Piston Undercrown Carbon Deposit Comparison, Cylinder 1, E0 on Left, E15 on Right......................... 23

Figure 20: Small End of Connecting Rod Carbon Deposit Comparison, E0 on Left, E15 on Right .......................... 23

Figure 21: Fuel Pump Check Valve Gasket Comparison, E0 on Left, E15 on Right................................................. 24

Figure 22: Fuel Pump Check Valve Comparison, E0 on Left, E15 on Right ............................................................. 24

Figure 23: Mineral Deposits in Cooling Jacket, E0 Verado 1B812775A ................................................................... 26

Figure 24: Verado Cylinder Head Indicating Where Head Gasket Failure Occurred, E0 Verado 1B812775A......... 26

Figure 25: Broken Exhaust Valve from E15 Verado 1B812776, Top Valve in Cylinder 3......................................... 27

Figure 26: Cracked Valves from E15 Verado 1B812776, Bottom Valve in Cyl. 3 Left, and Top Valve in Cyl. 6 Right

................................................................................................................................................................................... 27

Figure 27: Fatigue Initiation Sites on Cylinder 3 Bottom Exhaust Valve, E15 Verado 1B812776............................. 28

Figure 28: Heat Treatment Test of New Verado Valves............................................................................................ 29

Figure 29: Exhaust Valve Failure from Literature Research Showed Similar Failure Mechanism 8 ......................... 30

Figure 30: Photo of Section of Cylinder 3, E15 Verado 1B812776, Exhaust Ports on Left....................................... 31

Figure 31: Photo of Section of Cylinder 3, E0 Verado 1B812775A, Exhaust Ports on Left ...................................... 31

Figure 32: Exhaust Valve Lash (Measured Cold) vs. Endurance Time, E0 Substitute Engine................................. 32

Figure 33: Exhaust Valve Lash (Measured Cold) vs. Endurance Time, E15 Engine................................................ 33

Figure 34: 300HP Verado HC+NOx Emissions Results Summary ........................................................................... 34

Figure 35: 300HP Verado NOx Emissions Results by Mode Point, Representative Zero Hour Test Data............... 35

Figure 36: 300HP Verado HC Emissions Results by Mode Point, Representative Zero Hour Test Data................. 36

Figure 37: 300HP Verado CO Emissions Results by Mode Point, Representative Zero Hour Test Data................. 37

Figure 38: E0 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 Fuel................................ 38

Figure 39: E15 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 and E15 Fuel ............... 39

Figure 40: E15 Engine-Exhaust Gas Temperature Change at Wide Open Throttle, EEE-E0 to E15 Fuel............... 39

Figure 41: Piston Carbon Deposit Comparison, Cylinder 2, E0 on Left, E15 on Right ............................................. 40

Figure 42: Connecting Rod Carbon Deposit Comparison, Cylinder 2, E0 on Left, E15 on Right ............................. 41

Figure 43: Exhaust Cam Lobe Base Circle Detail, Cylinder 3, E0 on Left, E15 on Right ......................................... 42

Figure 44: 200HP EFI Bearing Failure Pictures ........................................................................................................ 43

Figure 45: 200HP Two-Stroke HC+NOx Emission Results Summary ...................................................................... 44

Figure 46: 200HP Two-Stroke CO Emission Results Summary................................................................................ 44

Figure 47: E0 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 Fuel................................ 45

Figure 48: E15 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 and E15 Fuel ............... 46

Figure 49: E15 Engine-Exhaust Gas Temperature Change at Wide Open Throttle, EEE-E0 to E15 Fuel............... 46

Figure 50: Cylinder 2 Wrist Pin Comparison, E0 on Left, E15 on Right .................................................................... 47

Figure 51: Emissions Comparison 4.3L V6 Catalyst Sterndrive, EEE vs. E15 ......................................................... 49
Page 4 of 52

Acknowledgements

This report and the work described herein were funded by the American Reinvestment and Recovery Act (ARRA) under 

stewardship of the Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Vehicle 

Technologies Program. The technical direction of Kevin Stork (Fuels Technology Team Lead) and Steve Przesmitzki is 

gratefully acknowledged. 

 

The National Renewable Energy Laboratory (NREL) provided Mercury with the opportunity to perform the work. Keith Knoll 

was excellent to work with as the Technical Monitor and is given thanks for the collaboration, technical guidance, and most 

importantly, patience.

The following people at Mercury Marine provided invaluable help with this project: Ed Alyanak, Ken Appleby, Terry Cleary, 

Mark Degler and the Metlab staff, Mike Docter and the ITC technicians, David Foulkes, Chris Jenks, Orrin Kimble and the 

engine lab technicians (esp.Ken Lemberger), Brian Merten and the dyno technicians (esp. Keith Hakala), Eric Mueller, Pete 

Neckuty, Tim Reid, Mark Riechers (program director), and Mike Torgerud. 
Page 5 of 52

Executive Summary 

Objective:

The objective of this work was to understand the effects of running a 15% ethanol blend on outboard marine engines

during 300 hours of wide-open throttle (WOT) endurance – a typical outboard marine engine durability test. For the 

three engine families evaluated, one test engine each was endurance tested on E15 fuel with emissions tests conducted 

on both E0 and E15 fuel, while a second control engine was emissions and endurance tested on E0 fuel for each engine 

family.

Summary of Results:

Results are based on a sample population of one engine per test fuel. As such, these results are not considered 

statistically significant, but may serve as an indicator of potential issues. More testing would be required to better 

understand the potential effects of E15.

9.9HP Carbureted Four-Stroke:

• The E15 engine exhibited variability of HC emissions at idle during end-of-endurance emissions tests, which 

was likely caused by lean misfire. 

o Both the E0 control engine and E15 test engine ran leaner at idle and low speed operation at the end of 

endurance testing compared with operation at the start of the test. 

o The trend of running lean at idle coupled with the additional enleanment from the E15 fuel caused the 

E15 engine to have poor run quality (intermittent misfire or partial combustion events) when operated 

on E15 fuel after 300 hours of endurance. 

o CO emissions were reduced when using E15 fuel due to the leaner operation, as expected for this 

open-loop controlled engine.

• The E15 engine exhibited reduced hardness on piston surfaces based on post-test teardown analysis.

o The exhaust gas temperature increased 17°C at wide open throttle as a result of the leaner operation 

when using E15 fuel. Higher combustion temperatures may have caused observed piston hardness 

reductions. Lack of pre-test hardness measurements prevented a conclusive assessment.

• Several elastomeric components on the E15 engine showed signs of deterioration compared with the E0 

engine. 

o Affected components were exposed to E15 fuel for approximately 2 months; signs of deterioration were 

evident.

300HP Four-Stroke Supercharged Verado:

• The E15 engine failed 3 exhaust valves close to the end of the endurance test. 

o Metallurgical analysis showed that the valves developed high cycle fatigue cracks due excessive metal 

temperatures. 

• The pistons on the E15 engine showed indications of higher operating temperatures compared to the E0 

engine’s pistons as evidenced by the visual difference in carbon deposits. 

• The E15 engine generated HC+NOx values in excess of the Family Emissions Limit (FEL) when operated on 

E15 fuel, but did not exceed that limit when operated on E0 emissions certification fuel.
Page 6 of 52

o The primary contributor to this increase in exhaust emissions was NOx due to enleanment caused by 

the oxygenated fuel. 

o CO emissions were reduced when using E15 fuel due to leaner operation, as expected for this openloop controlled engine. 

200HP EFI 2.5L Two-Stroke: 

• The 200 EFI two-stroke engine showed no signs of exhaust emissions deterioration differences due to the fuel.

o The E15 fuel caused the engine to run lean resulting in reduced HC and CO emissions. NOx was of 

little concern on this type of engine since NOx accounted for less than 2% of the total regulated 

HC+NOx emissions. 

• The E15 engine failed a rod bearing at 256 hours of endurance, which prevented completion of the 300 hour

durability test.

o Root cause of the bearing failure was not determined due to progressive damage.

o More testing would be necessary to understand the effect of ethanol on oil dispersion and lubrication in

two-stroke engines where the fuel and oil move through the crankcase together.

4.3L V6 EFI Four-Stroke Catalyzed Sterndrive: 

• Since E15 fuel was readily available in the test facility and an engine equipped with exhaust catalysts was on 

the dynamometer, emissions tests were conducted on a 4.3L V6 sterndrive engine to better understand the 

immediate impacts of ethanol on this engine family. 

o At rated speed and load (open-loop fuel control) E15 caused exhaust gas temperatures to increase by 

20°C on average and the catalyst temperatures to increase by about 30°C. 

o More rapid aging of the catalyst system occur due to the elevated catalyst temperature when 

considering the high load duty cycle typically experienced by marine engine applications.

Conclusions and Recommendations:

Several issues were discovered in this study from an exhaust emissions and an engine durability standpoint as a result 

of running E15 fuel in outboard marine engines. Run quality concerns were also identified as a result of the lean 

operation on the carbureted engine. 

Additional investigation is necessary to more fully understand the observed effects and to extrapolate them to all types of 

marine engines over broader operating conditions. Effects on operation at part load, transient acceleration/deceleration,

cold start, hot restart, and other driveability-related concerns need to be evaluated. This test program was mainly testing 

for end-of-life durability failures, which would not likely be the first issues experienced by the end users. A customer 

would likely be affected by run quality/driveability issues or materials compatibility/corrosion issues before durability 

issues. The wide range of technology used in marine engines due to the wide range of engine output will complicate this 

issue (Mercury Marine produces engines from 2.5HP-1350HP).

More testing is needed to understand how ethanol blends affect lubrication systems in two-stroke engines that have fuel 

and oil moving through the crankcase together. Crankcase oil dispersion is the only mechanism by which two-stroke 

engines of this architecture provide lubrication at critical interfaces such as bearings and cylinder walls. Ethanol may

have an effect on the dispersion or lubricity of the oil.

A better understanding of how long term storage affects ethanol blends in marine fuel systems would require more realworld testing. Marine vessels often go through long periods of storage that could affect the fuel systems given the fact 

that the ethanol portion can absorb water when exposed, especially in humid areas near saltwater. 
Page 7 of 52

Introduction

Project Background: 

This project was a cooperative effort to assess the feasibility for marine engines of increasing the allowable ethanol 

concentration in gasoline above the current legal limit of 10%. Specifically, a 15% ethanol / 85% gasoline fuel blend

(E15) was tested in current production and legacy outboard marine engines. Gaseous exhaust emissions and engine 

durability were assessed on a typical durability test cycle. Three separate engine families were evaluated. A 200HP EFI 

two-stroke engine was chosen to represent legacy product. A 9.9HP carbureted four-stroke engine and a 300HP 

supercharged EFI four-stroke engine represented current product. Two engines were tested from each family. One 

was operated on E15 fuel and the other was operated on E0 gasoline. Emissions data from each engine were obtained 

before, in the middle of, and after durability testing.

Summary of Marine Engine Considerations: 

Marine engines require unique considerations when altering the fuel supplied to operate the engine. Considering these 

engines are frequently used in remote locations (offshore fishing for example), it is critical to ensure that the fuel does not 

cause or contribute to an engine malfunction. Changes in fuel formulations and the resulting effects on marine engine 

operability are of high importance.

Outboard marine engines span a large range of rated power output and technology which yields significant complexity 

when trying to understand the effects of changing the fuel supplied to the engine. When all of the typical Mercury 

production engines and the Mercury Racing products are included (inboards and outboards), engines from 86cc, 2.5HP 

up to 9.1L 1350HP twin turbo configurations are produced. Mercury outboards (the focus of this study) range in output 

and design from the 2.5HP splash lubricated carbureted four-stroke engines to 350HP supercharged EFI four-stroke 

and 300HP direct fuel injected two-stroke engines. If sterndrive/inboard engines are considered, the technology list gets 

even broader. The non-racing sterndrive products range from 135HP carbureted 4 stroke to 430HP closed-loop 

catalyzed EFI 4 stroke with onboard diagnostics. The sales volumes of marine engines may be much smaller than 

automotive or small offroad utility engines, but the range of power (nearly 3 orders of magnitude) and the range of 

available technology of marine engines is much wider than these other categories individually. 

The marine application requires an engine that has high power density and remains durable at high speeds and loads. 

It is important to minimize the amount of weight added to the vessel from the powertrain to maximize the payload and 

minimize drag. Boat hull drag is considerable at typical boat operating speeds resulting in high engine speeds and loads 

for extended periods. The result of these factors leads to engines which are high performance and made from premium 

materials. Changing the fuel specification must be carefully considered to assure that durability is not sacrificed. Figure 

1 illustrates the power density of the Verado engine (the 300HP supercharged EFI engine family used in this study)

compared to automotive engines that were contemporary when the Verado engine was introduced for the 2005 model 

year. Figure 2 shows a relative comparison of the vehicle load curves of a boat with a planing hull to an automobile. 

The likelihood of experiencing problems as a result of extended operation at or near WOT are far more pronounced on a 

marine engine than an automotive engine due to the great difference in vehicle load curves.
Page 8 of 52

Figure 1: Power to Weight Comparison, Scatter Band Data Provided by FEV (FEV Motorentechnik GmbH)1

Marine

Competition

Engine weight 

- [kg]

Engine power [kW]

DIN 

70020 A Automotive

Verado 

300HP
Page 9 of 52

 

Figure 2: Example Load Curve Comparison (Automotive data – source 2, boat load data – internal Mercury source) 

Investigation Details

Statement of Problem:

Procedure:

The engine testing process began by preparing each engine. This included instrumentation of the test engines as well 

as performing some basic checks (varied by engine type). The instrumentation process included installation of an 

exhaust emissions probe that met the requirements of the EPA 40 CFR Part 91 regulations. 

Each engine was rigged onto an appropriate dynamometer and a break-in process was performed. The break-in 

consisted of increasing speed and load settings for approximately 2.5 hours total duration and was performed on E0 

gasoline for all engines. This was followed by a power run to determine the wide open throttle (WOT) performance of 

each engine. The power run was performed on E0 gasoline on all engines and also on E15 fuel for only the E15 test 

engines. The power run included speed points from 2000RPM up to the maximum rated speed of the engine. 

Once the WOT performance was checked, emissions testing was performed using reference-grade E0 gasoline (EEE 

fuel: EPA Tier II emissions reference grade fuel). The emissions tests were done in triplicate to check repeatability and 

were run in accordance with the EPA requirements set forth in 40 CFR Part 91. Emissions tests were also performed on 

the E15 engines in triplicate using the E15 test fuel. Although this E15 test fuel was not blended from the referencegrade E0 gasoline, these tests provide some comparison of exhaust emissions between E0 and E15 while minimizing 

engine-to-engine variability.

Following the above emissions checks, each engine was prepared for the durability testing. This included doing a basic 

visual inspection as well as some general engine power cylinder integrity checks (example: compression test and 

cylinder leak-down). These integrity checks were also repeated at the durability mid-point and end-of-life test point as 

well.

The first half of the durability test was then performed. Each engine was rigged in Mercury’s Indoor Test Center, which 

consisted of large endurance test tanks, air supply systems, and data acquisition systems. Each engine was fitted with 

the appropriate propeller to operate the engine approximately in the midpoint of the rated speed range at wide open 

0

20

40

60

80

100

120

140

160

10 20 30 40 50 60 70 80 90

Vehicle Speed (mph)

Required Engine Power (hp)

Boat 

Load 

Curve 

Automotive 

Load Curve 2
Page 10 of 52

throttle. The engine instrumentation was continuously monitored and the data was recorded for the duration of the 

endurance test. Operational shutdown limits were placed on critical channels (min/max engine speed, max coolant 

temperature, etc) to monitor the health of the engine for the entire durability test period. Periodic maintenance was

performed on each engine (as appropriate for the engine type: oil level checks and changes, accessory drive belts, etc). 

This maintenance was performed in an accelerated manner as compared with typical customer maintenance intervals 

since the durability testing causes accelerated wear as compared with typical customer use. These protocols are typical 

of those used by Mercury for any durability test.

Once the first half of the durability testing was completed, each engine was rigged on the dynamometer again. 

Emissions tests on the appropriate fuel(s) were performed according to the procedures described above. The tests 

were again performed in triplicate to be able to evaluate repeatability. Each engine also got a visual inspection and the 

general engine power cylinder integrity checks before being returned to durability testing.

After the midpoint emissions testing was completed, each engine was returned to the Indoor Test Center endurance 

tank to complete the second half of the durability testing. The testing was performed in the same manner as the first half 

of the durability portion. 

When the durability testing was complete, each engine was returned to the dynamometer for post-durability emissions 

tests on the appropriate fuel(s). A post-endurance WOT performance power run was also performed to compare with 

the pre-durability power run.

Finally, after all running-engine tests were completed, each test engine underwent a complete tear-down/disassembly 

and inspection. This inspection included checks and measurements to assess the degree of wear, corrosion issues, 

cracks, etc. on power cylinder components. Emphasis was placed on components that would be at risk due to the 

differences in the fuels (exhaust valves due to exhaust gas temperature differences, for example).

Test Engine Description:

The engines used for this testing were all built as new engines on the production line and were randomly selected. They 

were not specially built or hand-picked. The choice of engine families to include in this program was based on 

representing a wide range of technology, a wide range of power output, and a significant annual production volume. 

The final engine family selection was approved by the Technical Monitor at NREL. Two 4-stroke engine families were 

selected to represent current production engines. A two-stroke engine family was selected to represent “legacy” 

products. Table 1 summarizes each test engine configuration. 

The 9.9HP four-stroke engine is used on a wide range of applications from small fishing boats, inflatable boats, and as a 

“kicker” engine. A “kicker” engine is an auxiliary engine used for low speed boat maneuvering while fishing on a large 

boat which includes a larger engine (150+HP) for the main propulsion. The 9.9HP engine is considered a portable 

engine. It was selected for this testing due to high sales volume and the fact that it represents the typical architecture for 

many of Mercury’s small carbureted four-stroke offerings. It should be noted that the settings for the carburetors on both 

of the 9.9HP test engines were set and sealed at the carburetor manufacturer. They were not tampered with by any 

Mercury personnel and were run just as they would if they were used by the end customer. The only adjustment 

allowed was the idle throttle stop to set the idle speed, which is the only adjustment a customer has access to. 

The Verado engine is considered the “flagship” outboard product at Mercury Marine. The non-Racing version used in 

this study is available in power outputs ranging from 200-300HP. These engines are used on boats with single, dual, 

triple, and even quad engine installations ranging from multi-engine offshore fishing boats & US Coast Guard patrol 

boats, high speed bass boats, all the way to commercial fishing vessels and ferry boats. The supercharged 300HP 

Verado was selected for testing due to the high performance nature of its design and the demands of this market 

segment. The Verado engines had an open loop electronic fuel injection system with no user adjustment possible.

The 200HP EFI two-stroke engine represents the “legacy” two-stroke products. The 2.5L platform has been the basis 

for carbureted, crankcase fuel injected (which is the case for the test engines used), and direct cylinder injection models. 

The platform has roots that can be traced back to the 1970’s. This engine was selected for testing because of the large 

number of engines that have been built off of this platform over the last several decades and that it represents the typical 

architecture for a variety of Mercury’s two-stroke product. An engine configuration with an EFI fuel system was selected 

to improve consistency in testing. The 2.5L 200HP EFI engine had an open loop electronic fuel injection system with no 

user adjustment possible.
Page 11 of 52

Table 1: Test Engine Specifications

Engine Family 9.9HP Four-Stroke Verado 200HP EFI

Gas Exchange Process Four-Stroke Four-Stroke Two-Stroke

Power Rating at Prop 9.9HP 300HP 200HP

Cylinder Configuration Inline 2 Cylinder Inline 6 Cylinder 60 Degree V-6 Cylinder

Displacement 0.209 Liter 2.59 Liter 2.51 Liter

Fuel Induction System Single Carburetor 

w/Accelerator Circuit, 2 Valve 

per Cylinder, Single Overhead 

Cam

Supercharged Electronic Fuel 

Injected 4 Valve per Cylinder, 

Dual Overhead Cam, 

Electronic Boost Control, 

Electronic Knock Abatement 

Strategy

Electronic Fuel Injected with 

Oil Injection, Loop Scavenged

Porting, Crankcase Reed 

Induction, Electronic Knock 

Abatement Strategy

Dry Weight 108 lbs / 49 kg 635 lbs / 288 kg 425 lbs / 193 kg

Fuel Octane 

Requirement

87 Octane R+M/2 Minimum 

Required

92 Octane R+M/2 

Recommended, 87 Octane 

R+M/2 Minimum Required

87 Octane R+M/2 Minimum 

Required

Test Fuel Description:

The fuels used in the endurance testing were intended to be representative of typical pump-grade fuels that could be 

commonly available to the general consumer. The primary factors in sourcing the E15 test fuel were consistency of fuel 

properties for the duration of testing, consistency of ethanol content at 15%, octane performance that met specific 

requirements for each test engine, and a representative distillation curve to match charge preparation characteristics. 

The E15 test fuel was splash blended by our fuel supplier in one batch to ensure consistency throughout testing. The 

E0 and E15 endurance fuels were sourced from different suppliers; as such there were likely differences in the additive 

packages (including the concentration of additives) of the fuels. Since the primary duty cycle was wide open throttle 

endurance, the additive package differences likely had little influence on the test. Since the Verado engine had a 

premium fuel recommendation, the E15 fuel was blended at a target of 91 octane [R+M]/2. The blend stock used was a 

typical pump-grade fuel that the supplier used for retail distribution. The E0 fuels used for the endurance testing were

also typical pump-grade fuels that the fuel supplier had available for distribution. Both a Regular (87 octane [R+M]/2) 

and a Premium (91 octane [R+M]/2) fuel supply were maintained at Mercury for testing on this program and all other 

internal Mercury test programs. The emissions tests on E0 fuel were all performed using EPA Tier II EEE fuel sourced 

from specialty fuel manufacturer Johann Haltermann Ltd. 

Samples of several of the test fuels were sent to outside laboratories for analysis. The parameters that were considered 

were: the distillation curve (ASTM D86)3

, Research and Motor Octane (ASTM D26994 and D27005), density, and API 

gravity. In addition, NREL measured ethanol content via the Grabner IROX 2000 Gasoline Analyzer and ASTM D55016

for the E15 fuel. The Grabner IROX 2000 measures ethanol via infrared spectroscopy (per ASTM 58457

) and is valid in 

the range of 0 – 25% ethanol. The ASTM 55016 method uses gas chromatography and is only valid for high levels of 

ethanol (93% to 97% ethanol); it was used here only as a reference. In-house fuel samples were also taken and 

analyzed on the Petrospec GS-1000 analyzer. This analyzer was used to estimate the octane and measure the 

oxygenate concentration. Like NREL’s Grabner IROX 2000, the Petrospec GS-1000 operates on the infrared 

spectroscopy concept and determines the ethanol concentration (up to 15%) per ASTM D58457

. The results from the 

Petrospec machine were used as reference values only, primarily for quality control.

Table 2 shows the various measurements made on the test fuels from the different measurement laboratories. The 

majority of the parameters were within expected ranges for the tolerance of the measurements used. The ASTM 

D55016 procedure used at NREL showed that the ethanol concentration was 18%. The results from the 2 infrared 
Page 12 of 52

spectroscopy measurements from both NREL and Mercury showed concentrations of approximately 14%. The results 

from the 2 methods bracket the target concentration of 15%, which was the actual concentration that the fuel was 

blended to at the fuel supplier. Only one sample of E15 was analyzed, which was valid since all of the E15 fuel was 

blended in one batch. The data sets from the 87 octane bulk/pump fuel and the 91 octane bulk/pump fuel used on 

endurance, and the data from the EEE were from one load of fuel of the multiple loads of fuel of each type used during 

the duration of the testing. 

Table 2: Fuel Analysis Results

Fuel Analysis E15 Fuel EEE 87 Bulk Fuel 91 Bulk Fuel 

91 Bulk Fuel 

Repeat

Sample Date 10/21/2010 10/8/2010 10/15/2010 10/15/2010 2/10/2011

Fuel Analysis Performed at Outside 

Laboratory

Research Octane (ASTM D2699) RON 95.7 97.2 89.6 93.4

Motor Octane (ASTM D2700) MON 86.3 88.5 84.6 87.5

[R+M]/2 AKI 91.0 92.9 87.1 90.45

Density @ 15.5C kg/L 0.752 0.744

API Gravity °API 56.5 58.7

Fuel Analysis Performed at NREL

Ethanol Content (ASTM D5501) % 18+/-1%

Ethanol Content (IROX analyzer) % 14%

Fuel Analysis Performed at Mercury 

Marine

Petrospec analyzer 

(E15 data ave. of 2 samples)

Ethanol Content % 14.1% 0 0 0

RON RON 95.7 95.8 89.4 92.9

MON MON 84.7 87.7 83.3 87.2

[R+M]/2 AKI 90.2 91.7 86.4 90.1

Reid Vapor Pressure (Mercury analysis) PSI 8.5 9.0 10.8 10.7

The distillation curves for the various test fuels were also measured. The results can be seen in Figure 3 below. The 

data shown in Figure 3 were from the actual test fuels used in this testing. The distillation curve from the E15 fuel 

showed a large step change in the region of the boiling point of ethanol, as was expected. 
Page 13 of 52

Figure 3: Distillation Curves of Test Fuels

Engine Testing Results

9.9HP Four-Stroke: 

Endurance Test Results

The endurance testing on the 9.9HP engine family precipitated no significant failures. There were no incidents related to 

the test fuels reported on either engine. There were several parameters measured at the start, middle, and end of test to 

check the general health of the engine during the course of the endurance test. These included cranking compression, 

power cylinder leakdown, cam timing, and valve lash. All of these parameters remained relatively unchanged through 

the course of testing within the repeatability of the measurement techniques used. Several fuel-effect differences 

between the test engines, however, were discovered during the end of test teardown and inspection. These differences 

are summarized in the section below.

Emissions Testing Results

A summary of the emissions results are shown in Figure 4 below, with the 5 mode total weighted specific HC+NOx 

values plotted on the Y axis and the amount of endurance time on each engine plotted on the X axis. Each data point 

on the curve represents the average emissions value of the 3 emissions tests performed at each interval. The error bars 

represent the minimum and maximum values of the 3 emissions tests at each interval. The dashed yellow line shows 

Distillation Curve Comparison, ASTM D86

0.0

50.0

100.0

150.0

200.0

250.0

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percent Recovered (%)

Temperature (°C)

E15 Fuel EEE (10/8/10-Haltermann Data)

87 Bulk Fuel (Sample 10-15-10) Pure Ethanol Boiling Point
Page 14 of 52

the data from the E0 engine (serial number 0R364814). The solid red and blue lines show the emissions data from the 

E15 engine (serial number 0R352904) using E15 and E0 (EEE) fuels, respectively. Figure 4 shows that the E0 engine 

had significantly lower emissions than the E15 engine when run on the same fuel. After reviewing the history of the 

emissions audits on this engine family dating back to its introduction in 2005, both of these engines were within normal 

production variability. 

Figure 4: 9.9HP Four-Stroke HC+NOx Emissions Results Summary 

In order to better understand the emissions output, the HC, NOx, and CO constituents were broken out and plotted 

separately in Figures 5, 6, and 7 respectively. The values for each constituent are the five mode totals of each. 

Figures 5 and 6 show that the HC emissions predominantly defined the overall trends and variability in the total HC+NOx 

trends seen in Figure 4. The NOx data shown in Figure 6 had low test-to-test variability and the values were relatively 

flat (perhaps slightly declining for the E15 engine on E15 fuel) over the life of both engines.

Average HC+NOx Emissions Output: 9.9HP 4 Stroke

EEE and E15 Fuel

13

14

15

16

17

18

19

20

21

22

23

-30 0 30 60 90 120 150 180 210 240 270 300 330

Endurance Time [Hours]

Emissions [g/kw-hr]

E15 Engine EEE E15 Engine E15 Fuel E0 Engine EEE Fuel
Page 15 of 52

Figure 5: 9.9HP Four-Stroke HC Emissions Results Summary

Figure 6: 9.9HP Four-Stroke NOx Emissions Results Summary 

There was a general downward trend in CO over endurance time for the E15 engine on both fuels. The E0 showed 

some reduction in CO between 0 and 150 hours and remained relatively flat from 150 to 300 hours. The reduction in 

CO would suggest that the engines were running leaner since the primary driver for changing the CO emissions is 

typically the equivalence ratio. 

Average HC Emissions Output: 9.9HP 4 Stroke

EEE and E15 Fuel

10

11

12

13

14

15

16

17

18

19

20

-30 0 30 60 90 120 150 180 210 240 270 300 330

Endurance Time [Hours]

Emissions [g/kw-hr]

E15 Engine EEE E15 Engine E15 Fuel E0 Engine EEE Fuel

Average NOx Emissions Output: 9.9HP 4 Stroke

EEE and E15 Fuel

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

-30 0 30 60 90 120 150 180 210 240 270 300 330

Endurance Time [Hours]

Emissions [g/kw-hr]

E15 Engine EEE E15 Engine E15 Fuel E0 Engine EEE Fuel
Page 16 of 52

Figure 7: 9.9HP Four-Stroke CO Emissions Results Summary 

The enleanment over time trend predicted from the CO data in Figure 7 was confirmed in Figures 8 and 9 for both the 

E0 and E15 engines operated on EEE-E0 fuel in both cases. The interesting thing to note was that the primary modes 

that became leaner were modes 4 and 5. During the end of test inspection on both engines, wear on the throttle plates 

was found on the sides where the throttle shafts went through the carburetor bodies. The wear caused gaps around the 

throttle plates which allowed excess air to enter the engines at low throttle opening positions (high manifold vacuum), 

which included Modes 4 and 5. The amount of wear found was considered normal for the amount of endurance time 

the engines experienced and was found on both engines.

It should be noted that the E15 engine ran leaner than the E0 engine when operated on EEE-E0 fuel, as can be seen in

Figures 8 and 9 from a comparison of the “0 hour” equivalence ratios of both engines. This difference in equivalence 

ratio is considered to be in the normal production variability of this carbureted engine family.

 

Figures 8 & 9: Change in Equivalence Ratio vs. Endurance Time-EEE Fuel on E0 engine and E15 Engine 

Average CO Emissions Output: 9.9HP 4 Stroke

EEE and E15 Fuel

200

250

300

350

400

450

-30 0 30 60 90 120 150 180 210 240 270 300 330

Endurance Time [Hours]

Emissions [g/kw-hr]

E15 Engine EEE E15 Engine E15 Fuel E0 Engine EEE Fuel

Equivalence Ratio Change vs. Endurance Time, 

0R364814 "E0 Engine" EEE Fuel

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

0 1 2 3 4 5 6

Mode Point

Equivalence Ratio

0 Hour 150 Hour 300 Hour

Equivalence Ratio Change vs. Endurance Time, 

0R352904 "E15 Engine" EEE Fuel

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

0 1 2 3 4 5 6

Mode Point

Equivalence Ratio

0 Hour 150 Hour 300 Hour

Rich

Lean

Rich

Lean
Page 17 of 52

In addition, the equivalence ratio vs. endurance time data was plotted for the E15 engine when operated with E15 fuel in 

Figure 10. The graph shows the same trend of leaner operation vs. endurance time for Modes 4 and 5, as expected. 

However, when looking at the equivalence ratio values generated by the engine at Mode 5, it is clear that the engine ran 

very lean after 300 hours of endurance. This lean operation was the result of the inherent enleanment from the E15 fuel 

coupled with the trend of the engine to operate leaner with more endurance time due to the throttle plate wear.

Figure 10: Change in Equivalence Ratio vs. Endurance Time-E15 Fuel on E15 Engine

It is clear that both engines ran leaner with more endurance time, yet the HC emissions increased (on average) for the 

E15 engine using E15 fuel (see Figure 5). To get more understanding, the hydrocarbon emissions results from each 

individual emissions test were plotted out in Figures 11-13 for the E15 tests at 0, 150, and 300 hours of endurance, 

respectively. The difference in HC at the 300 hour emissions check was caused by the Mode 5 (idle) point as Figure 13 

shows. The high variability of HC emissions at Mode 5 may have been caused by poor run quality leading to intermittent 

misfire as the equivalence ratio trended further lean of stoichiometric (<0.925) with increasing run time. 

Equivalence Ratio Change vs. Endurance Time, 

0R352904 "E15 Engine" E15 Fuel

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

0 1 2 3 4 5 6

Mode Point

Equivalence Ratio

0 Hour 150 Hour 300 Hour

Rich

Lean
Page 18 of 52

Figures 11, 12, and 13: Hydrocarbon Emissions Outputs for Each Emissions Test, E15 Engine on E15 Fuel

Engine Performance Comparison

The power and torque data from the E0 9.9HP engine is shown in Figure 14 below. [Note: All power and torque curves 

were normalized to a set torque and power to make consistent comparisons possible across different engines, fuels, and 

amount of endurance time. The highest power and torque values generated on any of the tests were used as the 

reference power and torque setting and the runs were normalized back to these values.] There was a clear trend of 

increasing power and torque with more endurance time on the E0 engine. There was an increase of 3.2% in peak 

power and a 2.1% increase in peak torque when comparing the zero hour test with the 300 hour test. Similar graphs for 

the E15 engine are shown in Figure 15 on the E0-EEE fuel and in Figure 16 on the E15 fuel. Figures 15 and 16 show 

that there was generally a trend of decreasing power and/or torque with more endurance time on the E15 engine. On 

the E0-EEE fuel there was no change in peak power, but a loss of 1% peak torque when comparing the zero hour test 

with the 300 hour test on the E15 engine. Results on E15 fuel were similar, with a loss of peak power of 0.9% and a 

loss of peak torque of 2.1% when comparing the zero hour test with the 300 hour test. The mechanism that caused the 

E0 engine to have increasing power vs. endurance time and the E15 engine to have decreasing power vs. endurance 

time is unclear.

Hydrocarbon Emissions-Zero Hour Tests, 

0R352904 "E15 Engine" E15 Fuel

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4 5 6

Mode Point

Emissions (g/kw-hr)

Run 1 Run 2 Run 3

Hydrocarbon Emissions-150 Hour Tests, 

0R352904 "E15 Engine" E15 Fuel

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4 5 6

Mode Point

Emissions (g/kw-hr)

Run 4 Run 5 Run 6

Hydrocarbon Emissions-300 Hour Tests, 

0R352904 "E15 Engine" E15 Fuel

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4 5 6

Mode Point

Emissions (g/kw-hr)

Run 7 Run 8 Run 9
Page 19 of 52

Figure 17 shows a comparison of the fuel’s effect on the engine performance. The E15 fuel power run shows more 

torque generation throughout the speed range tested. There is approximately 1.75% more torque (and therefore, more 

power) on average throughout the speed range. Due to the enleanment from the fuel change, the engine may have 

been operating in a range closer to the Lean Best Torque on the E15 fuel and/or the volumetric efficiency may have

been improved due to the additional charge cooling afforded by the heat of vaporization difference of the fuels. Figure 

18 shows the difference in exhaust gas temperatures during the same power runs on the 2 different fuels. There was an 

approximately 17°C increase in EGT on both cylinders due to the enleanment from the E15 fuel.

Figure 14: E0 Engine Power and Torque Output at Endurance Check Intervals

Normalized Power and Torque Output

E0 Engine on E0-EEE Fuel, 9.9HP 4 Stroke 0R364814

0.8

0.85

0.9

0.95

1

1.05

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Engine Speed

Normalized Torque

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Normalized Power

Zero Hour Torque Midpoint Torque Endpoint Torque

Zero Hour Power Midpoint Power Endpoint Power
Page 20 of 52

Figure 15: E15 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 Fuel

Figure 16: E15 Engine Power and Torque Output at Endurance Check Intervals-E15 Fuel

Normalized Power and Torque Output

E15 Engine on E0-EEE Fuel, 9.9HP 4 Stroke 0R352904

0.8

0.85

0.9

0.95

1

1.05

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Engine Speed

Normalized Torque

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Normalized Power

Zero Hour Torque Midpoint Torque Endpoint Torque

Zero Hour Power Midpoint Power Endpoint Power

Normalized Power and Torque Output

E15 Engine on E15 Fuel, 9.9HP 4 Stroke 0R352904

0.8

0.85

0.9

0.95

1

1.05

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Engine Speed

Normalized Torque

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Normalized Power

Zero Hour Torque Midpoint Torque Endpoint Torque

Zero Hour Power Midpoint Power Endpoint Power
Page 21 of 52

Figure 17: E15 Engine Power and Torque Output, Zero Hour Check-E0-EEE Fuel vs. E15 Fuel

Normalized Power and Torque Output

E15 Engine Fuel Comparison, 9.9HP 4 Stroke 0R352904

0.8

0.85

0.9

0.95

1

1.05

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Engine Speed

Normalized Torque

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Normalized Power

E0-EEE Torque E15 Torque E0-EEE Power E15 Power
Page 22 of 52

Figure 18: E15 Engine-Exhaust Gas Temperature Comparison, Zero Hour Check-E0-EEE Fuel vs. E15 Fuel

End of Test Teardown and Inspection

When the running engine testing was completed, the engines were disassembled and inspected. The main areas of 

focus were looking for signs of wear or deterioration and also material compatibility issues.

Upon initial inspection, there were indications that some of the main engine components on the E15 engine were 

subjected to higher operating temperatures. There were more carbon deposits observed on the undercrown area of the 

pistons and the small end of the connecting rod, suggesting that the pistons were operating at a higher temperature. 

Comparisons of the pistons and rods can be seen in Figures 19 and 20, respectively.

2000 2500 3000 3500 4000 4500 5000 5500 6000 6500

Speed 

EGT Cyl 1 [°C]

450

480

510

540

570

600

630

660

690

720

750

Speed

TEMani01

TEMani01

rpm

°C

°C

 6000

 715

 732

2000 2500 3000 3500 4000 4500 5000 5500 6000 6500

Speed 

EGT Cyl 2 [°C]

450

480

510

540

570

600

630

660

690

720

750

0R352904 EEE-E0 Fuel

0R352904 E15 Fuel

Speed

TEMani02

TEMani02

rpm

°C

°C

 6000

 700

 717

Exhaust Gas Temperature Comparison

0R352904 E15 Engine, Various Fuels

Zero Hour WOT Power Run
Page 23 of 52

Figure 19: Piston Undercrown Carbon Deposit Comparison, Cylinder 1, E0 on Left, E15 on Right

Figure 20: Small End of Connecting Rod Carbon Deposit Comparison, E0 on Left, E15 on Right

Although there were no indications of fuel pump failure during engine test, the mechanical fuel pumps were also 

disassembled and inspected following testing to look for abnormal signs of wear or degradation. The check valve 

gasket on the E15 engine showed signs of deterioration compared with that from the E0 engine. The gasket from the 

E15 pump had a pronounced ridge formed in the area that “hinged” when the check valve was in operation (see notes in 

Figure 21). The E15 gasket material in the area that sealed the check valve also had signs of wear that were more 

advanced than the E0 gasket. There was a significant amount material transfer from the gasket to the plastic check 

valve that it sealed as shown in Figure 22. Both fuel pumps were exposed to their respective test fuels for a period of 

approximately 2 months. More investigation is necessary to understand the effects of long term exposure of these 

components. It should be noted that the fuel pump flow performance was not tested. There were no indications that 

there was a problem with the fuel pump before disassembly. Once the deterioration was noted during teardown, it was 

determined that measuring the flow performance after disassembly and subsequent reassembly would have likely 

introduced error in the measurement.
Page 24 of 52

Figure 21: Fuel Pump Check Valve Gasket Comparison, E0 on Left, E15 on Right

 

Figure 22: Fuel Pump Check Valve Comparison, E0 on Left, E15 on Right

Due to the visible differences in some of the engines’ metal components, several components were sent to the in-house 

metallurgy lab for further analysis. Results of this analysis are included in Table 3. The Vickers hardness test was

performed using a Clemet Microharness Tester with a conversion to the Rockwell C scale where applicable (on steel 

parts). The Brinell scale was used for the aluminum parts, as they are much softer than the steel parts. The values 

shown were the average of 3 measurements for each component with the exception of the valve bridge in the cylinder 

head where only 2 measurements were taken. However, due to the fact that only 1 component from each engine on the 

2 fuels was tested the results have no statistical significance and should be taken as an indicator only. Also, no 

hardness measurements were taken on the components prior to testing so there was likely some normal part-to-part 

variability in hardness as the components were originally manufactured. 

Taking all of these issues into consideration there were indications that some of the components had different hardness 

values. These differences were most likely related to the continuous operating temperatures of the components. The 

most notable differences were the pistons, the valve bridge in the cylinder head and the intake valve stems. The piston 

measured from the E15 engine had a hardness value approximately 13.2% lower than the piston from the E0 engine. 

This would suggest that the E15 piston experienced a higher operating temperature, as expected due to the lean 

Ridge formed at 

“hinge” area.

More 

deterioration

No ridge formed on 

E0 gasket

Material retains more of original 

surface finish on E0
Page 25 of 52

operation. The carbon deposits on the underside of the piston due to oil coking also suggest the E15 pistons were 

running hotter as noted previously. The intake valve stem measurements showed an approximately 12% difference in 

hardness, with the E0 engine having the lower values. This difference would suggest that the E0 intake valve stems 

were running hotter during operation than the E15. This difference was likely due to the charge-air cooling effect of 

ethanol in the E15 fuel resulting in cooling of the intake port and leading to lower intake valve stem temperatures. The 

evaporative cooling in the intake port could also explain why the valve bridge hardness measurements indicated that the 

valve bridge on the E15 engine had lower operating temperatures evidenced by the roughly 11% higher hardness value. 

The other measurements showed differences that were likely within the repeatability of the measurements and the 

manufacturing variability so no conclusions could be drawn from them. 

The piston is generally a higher-stressed component than the intake valve. The reduction in hardness of the intake 

valve for the E0 engine is not likely to increase failure rates since this engine family was qualified for E0 operation as a 

baseline. However, if the reduction in hardness of the piston with E15 fuel was found to be a statistically significant 

result, E15 fuel usage might increase the failure rate of this component. 

Table 3: Hardness Measurements on Various 9.9HP Four-Stroke Engine Components

9.9HP Four Stroke

Hardness 

Scale

E0

0R364814

E15

0R352904

Percent 

Difference

Piston, Cyl 1 BHN 91.0 79.0 13.2%

Connecting Rod, Small End Cyl 1 BHN 112.0 112.0 0.0%

Exhaust Valve Stem, Cyl 1 Rc 21.7 22.1 -2.0%

Exhaust Valve Head, Cyl 1 Rc 30.1 30.7 -2.0%

Valve Bridge in Cyl. Head, Cyl 1 BHN 83.0 92.0 -10.8%

Intake Valve Stem, Cyl 1 Rc 33.0 36.9 -11.9%

Intake Valve Head, Cyl 1 Rc 39.6 39.1 1.3%

Verado 300HP Supercharged Four-Stroke: 

Endurance Test Results

Several engine failures occurred during endurance testing on the Verado engines, two of which were not related to the 

fuel and one of which may have been associated with the use of E15 fuel. The two non-fuel-related engine failures 

included a casting defect and a test facility induced failure. A third engine failure, involving failed exhaust valves is 

believed to have been caused by the E15 fuel. Failure mechanisms are described in detail below. 

E0 Engine #1-Casting Defect: The first engine to fail was the E0 Verado-serial number 1B812775. At 177 hours of WOT 

endurance (204.2 total engine hours) the engine was shut down for a routine oil check. An excessive amount of water 

was found in the oil. The engine was disassembled and the major components were pressure checked. A leak path 

was discovered from the water jacket to the intake port on one cylinder. The cylinder head was sectioned and an oxide 

fold line from the casting process was discovered. This defect was present from the time of the original casting process 

and took thermal cycling, load, and time to cause a leak. It was in no way associated with the fuel.

E0 Engine #2-Test Facility-Induced Failure: An additional engine was obtained to replace the original E0 engine and this 

engine was given the serial number 1B821775A. This engine did the initial dyno tests and was put on endurance. After 

88.7 hours of WOT endurance (98 total engine hours), the engine was automatically shut down by the endurance facility 

control system for low exhaust gas temperature. Investigation showed water entering the exhaust stream. The engine 

was then disassembled and a significant amount of mineral deposits were found in the cooling passages, especially in 

the exhaust collector on the cylinder head. See Figure 23. [Note: For a coolant fluid, outboard engines draw in water

from the body of water they are operating in, which in this case was the endurance test tank.] An interaction between 
Page 26 of 52

the pH and hardness of the water in the test tank created conditions that precipitated out minerals (primarily calcite) 

when exposed to the elevated temperatures in the cooling passage, especially near the exhaust collector. The blocked 

passages prevented adequate cooling in the exhaust collector, which eventually failed the head gasket and allowed 

water to enter into the exhaust stream. See Figure 24. It should be noted that these water chemistry conditions were 

specifically caused by the test facility water conditioning and would not be something that the engine would experience 

in real-world use.

Figure 23: Mineral Deposits in Cooling Jacket, E0 Verado 1B812775A

Figure 24: Verado Cylinder Head Indicating Where Head Gasket Failure Occurred, E0 Verado 1B812775A

E15 Engine: At 285 hours of endurance operation (323 total engine hours), the E15 Verado test engine (serial number 

1B812776) was noted to have rough idle after restarting shortly after maintenance was performed. A compression 

check was performed showing no compression on cylinder 3. During disassembly a broken exhaust valve was found in 

cylinder #3. Further investigation found that the other exhaust valve on cylinder 3 had developed a crack, as well as one 

Cyl 1 Cyl 6

Integral Exh. Manifold

Exh. Collector where Head 

Gasket was Damaged
Page 27 of 52

of the exhaust valves in cylinder 6. See Figures 25 and 26. NOTE: The images shown in Figure 26 of the cracked 

exhaust valves had been cleaned of deposits prior to photography.

 

Figure 25: Broken Exhaust Valve from E15 Verado 1B812776, Top Valve in Cylinder 3

 

Figure 26: Cracked Valves from E15 Verado 1B812776, Bottom Valve in Cyl. 3 Left, and Top Valve in Cyl. 6 Right

The cracked valves and several valves without cracks from the E15 Verado were analyzed in Mercury’s materials 

laboratory. The cracked valves were visually inspected with an optical stereoscope. The fatigue initiation sites were 

clearly identified. Figure 27 shows an example of the images of the initiation sites from the bottom exhaust valve from 

cylinder 3.
Page 28 of 52

Figure 27: Fatigue Initiation Sites on Cylinder 3 Bottom Exhaust Valve, E15 Verado 1B812776

In addition to finding the fatigue initiation sites, the failed valves were checked for hardness. The cracked valves from 

the E15 engine were found to have hardness values much lower than new valves and below the minimum print 

specification of a new valve. Other sample valves were collected and analyzed from WOT endurance Verado engines 

that were run on E0 pump fuel during the same general timeframe as the E15 engine was run. In addition, samples of 

new valves were also acquired and analyzed. The hardness measurements showed that the valves from the engines 

operated on E0 fuel were actually harder than the new valves. The summary of hardness measurements are shown in 

Table 4. Note: All of the measurements were taken in the Rockwell A scale and converted to the Rockwell C scale due 

to the fact that the samples were mounted and polished to perform hardness measurements in the center of the cross 

section. This would negate any hardness effects from the mounting material.

Table 4: Verado Exhaust Valve Hardness Measurement Summary 

Valve Description Hardness (HRC)

E15: 1B812776 Cyl 3 Bottom 22

E15: 1B812776 Cyl 6 Top 22

E0: 1B812775 Cyl 3 Bottom 37.5

E0: 1B812775 Cyl 3 Top 36.5

E0: 1B812775A Cyl 3 Top 38

E0: 1B828629 Cyl 2 Top 37.5

New Valve #1 34.5

New Valve #2 34.5

New Valve #3 33

New Valve #4 33

New Valve #5 33.5

The Verado exhaust valves are made from Inconel 751, which is a heat-treatable alloy. This trait was used to estimate 

the metal temperatures experienced by the valves. The valve hardness data in Table 4 collected from the E0 engines
Page 29 of 52

suggested that the metal temperatures experienced during operation were in a range that allowed age-hardening of the 

metal to make the valves increase in hardness. The hardness values of the E15 engine valves suggested that they 

were operating in a temperature regime that significantly reduced the hardness. In order to understand the hardness 

versus temperature, the new valves that were hardness checked were heated in an oven for 24 hours at various 

temperatures and then hardness was checked again. Figure 28 shows the results from the oven heating operation on

the new valves. In Figure 28, the blue line shows the hardness data of the new valves before heat treatment and the red 

line shows the hardness data of the valves after heating. At metal temperatures above 870°C, the valves showed a 

dramatic decline in hardness according to this test data. The data suggest that the exhaust valves from the E15 engine 

may have experienced temperatures nearing 900°C.

One possible mechanism by which the E15 exhaust valves may have experienced such high temperatures would be a 

disruption of valve cooling during the portion of the cycle where the valve should be fully seated. During inspection, it 

was noted that several cam lobes showed wear and marking on the base circle portion of the lobe indicating that the 

exhaust valves had run out of lash. This suggested that excessive wear or valve head deformation may have occurred

during operation, which caused the lash to diminish. This would have prevented the valve from seating properly 

resulting in a significant valve temperature increase due to lack of cooling on the seat. The valves or seats may have 

also had accelerated wear to diminish the lash due to lack of lubricity of the E15 fuel or because of the elevated 

temperatures caused by the lean operation on E15 fuel. In addition, if the exhaust valves were experiencing higher 

operating temperatures due to the higher exhaust gas temperatures from using E15 fuel, the overall length of the valve 

would be slightly longer. This longer length during operation would also reduce the amount of lash in the valvetrain and 

make the engine more prone to base circle contact on the cam. Plots comparing the measured cold valve lash over the 

course of endurance between the E0 and E15 engines are shown in Figures 32 and 33 below. 

Figure 28: Heat Treatment Test of New Verado Valves

Verado Exhaust Valve Heat Treatment Test, New Valves, 

24 Hour Heat Treatment Duration

40

45

50

55

60

65

70

75

750 800 850 900 950 1000

Temperature of Heat Treat (deg C)

Hardness (Rockwell A)

Before Heat Treat After Heat Treat

40 HRC

20 HRC
Page 30 of 52

Figure 29: Exhaust Valve Failure from Literature Research Showed Similar Failure Mechanism 8

Similar failure mechanisms were found in a literature search as shown in Figure 29. The failure is noted as a classic 

over-temperature failure. “High temperatures and a corrosive environment at the exhaust fillet substantially weaken the 

valve strength.” 8 from: Introduction to Engine Valvetrains by Yushu Wang

Extensive development went into the valvetrain on this high-output engine. Upgrading the engine to account for higher 

exhaust gas temperatures due to a wider range of fuel properties would not be easily accomplished. The current 

production Verado exhaust valve is Inconel 751, which is categorized in the “superalloy” material classification. 

It should be noted that the E15 engine (1B812776) was operating for a period of time when the mineral precipitation 

problem occurred on the second E0 engine (1B812775A). However, it is not believed that this contributed to the valve 

failure. The E15 engine (1B812776) did have some accumulation of precipitation flakes in the exhaust collector area, 

but not nearly to the extent that the E0 engine did. The E15 engine (1B812776) was not operating the entire time the E0 

engine (1B812775A) ran when the mineral precipitation problem occurred. The head was sectioned and there were no 

mineral precipitation deposits on cooling jacket surfaces in cylinder 3 where the worst valve failure occurred. See Figure 

30 for a picture of the sectioned head from the E15 engine (1B812776) showing no mineral deposits were present. 

Yellow spots in the cooling jacket were anti-corrosion coating from production where the paint did not fully coat interior 

surfaces of the cooling jacket. Figure 31 shows the same section of cylinder head from the E0 engine (1B812775A) that 

failed due to the mineral precipitation. This E0 engine (1B812775A) was also inspected for cracked exhaust valves and 

none were found. In addition, the hardness values of the exhaust valves were measured (see Table 4) indicating that 

the mineral precipitation issue did not affect the valve hardness on the E0 engine (1B812775A). There were several 

other Verado engines that were running endurance testing for a different project that failed due to the mineral 

precipitation issue. All other Verado engines that failed due to the mineral precipitation failed the head gasket in the 

exhaust collector area.
Page 31 of 52

Figure 30: Photo of Section of Cylinder 3, E15 Verado 1B812776, Exhaust Ports on Left

Figure 31: Photo of Section of Cylinder 3, E0 Verado 1B812775A, Exhaust Ports on Left

Cooling Jacket
Page 32 of 52

E0 Substitute Engine: In lieu of a completed test on E0 fuel, a substitute engine was chosen that had already been 

through endurance testing (serial number 1B828592). The engine that was used as a substitute had completed 372 

hours of WOT endurance testing and was still intact. It ran in the same test facility running under the same test 

procedure as all other endurance testing as part of this project. The engine was used for a gearcase durability test for a 

different project so the rest of the engine was completely stock and built on the production line as were the other engines 

in this project. As such, it provided a suitable replacement for the incomplete E0 tests. For reference, the replacement 

engine (1B828592) was on test between the following dates: 11/15/2010 through 12/14/2010. The E15 engine 

1B812776 was on test between 9/21/2010 through 11/12/2010.

As part of routine maintenance and checks during endurance, several valve lash measurements were taken at various 

intervals on the E0 substitute engine. Figures 32 and 33 below show the lash measurements during the course of 

endurance for both the E0 substitute engine (1B828592) and the E15 engine (1B812776), respectively. The solid red 

lines in the graph indicate the upper and lower lash specification on a new engine. It is clear from the lash 

measurements on the 2 engines that the E15 engine had a significantly faster decline in lash than the E0 substitute 

engine. The E0 substitute engine had 1 valve with higher lash value at the end of testing. There may have been some 

carbon or other deposits holding this valve off the seat during the measurement. 

Figure 32: Exhaust Valve Lash (Measured Cold) vs. Endurance Time, E0 Substitute Engine

1B828592 E0 Verado Substitute, Exhaust Valve Lash

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0 50 100 150 200 250 300 350 400

Engine Run Time (Hours)

Valve Lash (mm)

Lower Spec Upper Spec 1A 1B 2A

2B 3A 3B 4A 4B

5A 5B 6A 6B
Page 33 of 52

Figure 33: Exhaust Valve Lash (Measured Cold) vs. Endurance Time, E15 Engine

Emissions Testing Results

Due to failures of both the E0 and E15 engines, a complete analysis of the deteriorated emissions was not possible. 

However, with the data available several conclusions could be made. Figure 34 shows a graph of the Verado emissions 

that were collected. As was the case for the 9.9HP emissions data plots, each data point on the curve represents the 

average emissions value of the 3 emissions tests performed at each interval with error bars showing the range of the 3 

emissions tests. The dashed yellow line shows the data from the original E0 engine (serial number 1B812775). The 

solid red and blue lines show the emissions data from the E15 engine (serial number 1B812776) using E15 and E0 

(EEE) fuels, respectively. The single point in light blue at 372 hours shows the end of test emissions results for the 

substitute E0 engine (EEE fuel, serial number 1B828592). The graph shows a generally declining HC+NOx trend for the 

2 original engines which is typical of Verado engines. The declining emissions trends on both engines would suggest 

that the ethanol fuel blend did not adversely affect the emissions deterioration on the Verado engine. The most notable 

aspect of the emissions output on the E15 engine was the fact that the total HC+NOx on E15 fuel was above 25 g/kw-hr, 

whereas the value on EEE-E0 was 21.5 g/kw-hr. The Family Emissions Limit (FEL) was set to 22 g/kw-hr for this engine 

family. A Verado engine generating 25 g/kw-hr would have failed an emissions audit. The increase in emissions can be

primarily attributed to a significant increase in NOx due to the lean operation. Since the Verado is a highly boosted 

engine it is very sensitive to NOx generation due to changes in equivalence ratio. However, there was also an increase 

in HC emissions due to the E15 fuel, which would not be expected with a leaner equivalence ratio.

1B812776 E15 Verado, Exhaust Valve Lash

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0 50 100 150 200 250 300 350 400

Engine Run Time (Hours)

Valve Lash (mm)

Lower Spec Upper Spec 1A 1B 2A

2B 3A 3B 4A 4B

5A 5B 6A 6B
Page 34 of 52

Figure 34: 300HP Verado HC+NOx Emissions Results Summary

In order to better understand the differences in the emissions outputs between the 2 fuels, graphs were made for each 

constituent of interest. Figures 35 through 37 show the NOx, HC, and CO emissions differences. The graphs were 

broken down by mode point for emissions tests performed prior to endurance on the E15 engine (1B812776). The 

values shown are the averages of the three repeated runs at “zero” hours.

Figure 35 shows the NOx emissions trends for the 2 fuels. The main differences were at Modes 1 and 2 which were 

both high load, boosted operating points. The fact that the NOx increased significantly with a lean shift due to the 

ethanol fuel blend was not surprising. Modes 3 and 4 did not show much difference because the engine was calibrated 

near an equivalence ratio of 1 on E0 fuel. The NOx trend with respect to equivalence ratio was near the peak at these 

points so a lean shift did not result in a significant change in NOx. Mode 5 was idle so the NOx generation at that point 

was essentially zero.

Average HC+NOx Emissions Output: 300HP Verado

EEE and E15 Fuel 

15.0

17.0

19.0

21.0

23.0

25.0

27.0

-25 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400

Endurance Time [Hours]

Emissions [g/kw-hr]

E15 Engine, EEE Fuel: 1B812776 E15 Engine, E15 Fuel: 1B812776

E0 Engine, EEE Fuel: 1B812775 E0 Substitute, EEE Fuel: 1B828592
Page 35 of 52

Figure 35: 300HP Verado NOx Emissions Results by Mode Point, Representative Zero Hour Test Data

The increase in HC output on E15 fuel was not an expected outcome of the test. Figure 36 highlights the difference in 

HC emissions between the 2 fuels. The main difference occurred at Mode 3, so further investigation was necessary into 

Mode 3 data specifically. However, it was also apparent that the HC output on E15 fuel was higher at Modes 1-4 

despite the leaner operation from the fuel chemistry. This may suggest that the vaporization of the E15 fuel was inferior 

to that of the EEE fuel leading to poor fuel preparation. This is supported by data from Modes 1 and 2 where NOx and 

CO trends show that the engine did run leaner, yet had higher HC output when operated with E15. 

The HC difference at Mode 3 was likely a result of the engine running substantially leaner than lean best torque (LBT). 

In this operating region, the Verado engine is calibrated slightly lean of the stoichiometric mixture on E0 fuel. With the 

use of E15 fuel, the engine operates significantly lean of LBT and, therefore, the torque production diminishes 

significantly. As a result, to achieve the specified torque set point for Mode 3 the throttle input had to be increased, 

yielding higher airflow and higher fuel flow. The fuel flow increased nearly 10% for essentially the same torque 

production with E15 fuel. In addition, it was noted that the intake air temperature was 12°C cooler at Mode 3 with E15 

fuel. The cooler charge temperature was likely a result of the increased fuel vaporization cooling effect from the ethanol. 

The cooler temperatures in the intake may have impaired fuel preparation. The higher fuel flow combined with the 

inferior fuel preparation was likely the cause of the high HC output at Mode 3. 

Oxides of Nitrogen Emissions vs. Mode Point, Average of Zero 

Hour Emissions Tests, E15 Engine 1B812776

0

2

4

6

8

10

12

0 1 2 3 4 5 6

Mode Point

Emissions Output (g/kw-hr)

E0-EEE Fuel E15 Fuel
Page 36 of 52

Figure 36: 300HP Verado HC Emissions Results by Mode Point, Representative Zero Hour Test Data

The CO emissions vs. emissions test mode point are shown in Figure 37. There was a significant reduction in CO 

emissions at Modes 1 and 2 when the engine was operated on E15 fuel, as expected. Modes 1 and 2 are calibrated 

rich of a stoichiometric mixture on E0, so the enleanment from E15 caused a reduction in CO. Modes 3-5 are generally 

insensitive in regard to CO because the operating points are calibrated near the stoichiometric mixture, so leaning the 

engine out due to the fuel had little effect at reducing CO relative to the changes seen at Modes 1 and 2.

Hydrocarbon Emissions vs. Mode Point, Average of Zero Hour 

Emissions Tests , E15 Engine 1B812776

0

0.5

1

1.5

2

2.5

0 1 2 3 4 5 6

Mode Point

Emissions Output (g/kw-hr)

E0-EEE Fuel E15 Fuel
Page 37 of 52

Figure 37: 300HP Verado CO Emissions Results by Mode Point, Representative Zero Hour Test Data

Engine Performance Comparison

Due to the engine failures, a complete comparison of engine performance vs. run time was not possible. The 

normalized power and torque data from the E0 Verado is shown in Figure 38. The changes from zero hours to 150 

hours were less than 1% for peak torque (negligible) and a 2.3% reduction in peak power. The E0 engine produced less 

power output than the E15 engine when operated on the same E0 fuel. This difference of approximately 2% is 

considered normal production engine-to-engine variability.

Carbon Monoxide Emissions vs. Mode Point, Average of Zero 

Hour Emissions Tests, E15 Engine 1B812776

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6

Mode Point

Emissions Output (g/kw-hr)

E0-EEE Fuel E15 Fuel
Page 38 of 52

Figure 38: E0 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 Fuel

Power and torque data (normalized) for the E15 engine on both EEE-E0 fuel and E15 fuel is shown in Figure 39. There 

was an improvement in peak torque of 3.0% and in peak power of 1.5% when comparing the zero hour and midpoint 

runs on E0-EEE. The E15 engine showed negligible differences when comparing the midpoint power runs on E0-EEE 

and E15. It is unclear why this engine seemed unresponsive to the differences in charge cooling afforded by the ethanol 

blend fuel. Note: There was not a power run completed on E15 fuel at the initial zero hour measurement, which is why 

the midpoint data is compared in these figures.

Normalized Power and Torque Output

E0 Engine on E0-EEE Fuel, 300HP Verado 1B812775

0.75

0.8

0.85

0.9

0.95

1

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Speed

Normalized Torque

0.75

0.8

0.85

0.9

0.95

1

Normalized Power

Zero Hour Torque Midpoint Torque

Zero Hour Power Midpoint Power
Page 39 of 52

Figure 39: E15 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 and E15 Fuel 

Figure 40 shows the difference in exhaust gas temperatures during power runs at the midpoint check on the 2 different 

fuels. There was up to a 30°C increase in EGT when operating on E15 fuel. 

Figure 40: E15 Engine-Exhaust Gas Temperature Change at Wide Open Throttle, EEE-E0 to E15 Fuel

Normalized Power and Torque Output

E15 Engine on Both Fuels, 300HP Verado 1B812776

0.75

0.8

0.85

0.9

0.95

1

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Speed

Normalized Torque

0.75

0.8

0.85

0.9

0.95

1

Normalized Power

E0 Fuel-Zero Hour Torque E0 Fuel-Midpoint Torque E15 Fuel Midpoint Torque

E0 Fuel-Zero Hour Power E0 Fuel-Midpoint Power E15 Fuel Midpoint Power

Change in Exhaust Gas Temperature due to 

E15 Use, 300HP Verado 1B812776

0

5

10

15

20

25

30

35

0 0.2 0.4 0.6 0.8 1 1.2

Normalized Speed

Change in EGT [E15-E0] (°C)
Page 40 of 52 

End of Test Teardown and Inspection 

After all running engine tests were completed, the engines were disassembled and inspected. There was visual 

evidence that some of the internal components from the Verado E15 engine had experienced higher operating 

temperatures. 

Upon disassembly, there were differences noted in the condition of the pistons from the 2 engines. Figure 41 shows 

pictures comparing the pistons from cylinder 2 from each engine. The piston from the E15 engine had a significantly 

higher amount of oil staining and carbon deposits than the piston from the E0 engine. The staining and deposits were 

noted on nearly every surface of the E15 piston compared with the E0 piston. Additionally, the pistons were sent to the 

metallurgy lab for hardness measurements. The hardness measurements were taken at several locations on the crown 

of the piston as well as a location on the internal portion of the piston just above the wrist pin bore after being sectioned. 

The average crown hardness of the E0 piston was 67.5 BHN (Brinell Hardness Number) while the E15 piston crown 

was 66.9 BHN. The internal piston hardness above the wrist pin bore was 74.1 BHN for the E0 piston and 71.5 BHN for 

the E15 engine’s piston. Although the hardness measurements showed no effect of operating temperature on material 

properties, differences in visual appearance suggest that the E15 pistons operated at higher temperatures during 

running than the E0 pistons. 

Figure 41: Piston Carbon Deposit Comparison, Cylinder 2, E0 on Left, E15 on Right 

Figure 42 shows the small end of the connecting rods from each engine. The carbon deposits indicate that the E15 rods 

likely ran at higher operating temperatures. The carbon deposits on the rods are consistent with the carbon deposits 

observed on the pistons. 
Page 41 of 52

Figure 42: Connecting Rod Carbon Deposit Comparison, Cylinder 2, E0 on Left, E15 on Right

The exhaust valves were also closely inspected on the substitute E0 engine in order to compare with the valves that 

cracked on the E15 engine. With 372 hours of endurance aging time accumulated, no cracked valves were discovered 

during inspection under a microscope. The average hardness values of the exhaust valves from cylinder three of the E0 

engine were 37.3 and 37.7 HRC. These values were consistent with other engines that were operated on E0 as 

indicated in Table 4. 

During disassembly, the E15 engine was noted as having base circle contact on several of the exhaust cam lobes as 

noted above. The exhaust cam lobes from the substitute E0 engine did not show signs of base circle contact. The lash 

measurements shown in Figures 32 and 33 support these observations. A picture showing the difference in wear on the 

base circles of the exhaust cam lobes can be seen in Figure 43. The picture shows the E15 exhaust cam on the right 

and the E0 cam on the left. The wear pattern on the E15 exhaust cam lobe is apparent.
Page 42 of 52

Figure 43: Exhaust Cam Lobe Base Circle Detail, Cylinder 3, E0 on Left, E15 on Right

200 EFI Two-Stroke: 

Endurance Test Results

An engine failure prevented successful completion of the full endurance period for the 200 EFI E15 engine. The 200 EFI 

E15 engine failed a rod bearing before the completion of the endurance test. The 200 EFI E0 engine completed the 300 

hour endurance test and all post-endurance dynamometer tests.

The E15 endurance engine failed at 283 total engine hours and had accumulated 256 hours of WOT endurance at the 

time of failure. Upon inspection it was found that the big end connecting rod bearing had failed on cylinder 3. The rod 

cap was still bolted to the rod after the failure. This engine family uses a fractured rod cap design with a roller bearing 

(typical for a two-stroke vs. a plain bearing in a four-stroke). Images of the remaining bearing cage and the damaged 

rod along with undamaged pieces for reference are shown in Figure 44. No rollers were found during teardown and 

were likely ejected from the bearing and made their way through the power cylinder and out the exhaust. There was 

extensive damage to the top of the piston on cylinder 3 indicating that the rollers went through the power cylinder. Due

to the extensive damage to the bearing and connecting rod (since it failed at rated speed, full power) and the fact that not 

all of the pieces were recovered, root cause of the bearing failure was not conclusively determined. Little is known about 

the effects of ethanol blends on oil/fuel mixing and dispersion on total loss lubrication systems, such as the one on this 

engine family. More investigation is needed to understand if ethanol would negatively impact the lubrication systems on 

two-stroke engines. 

E0 E15

Base 

Circle 

Contact
Page 43 of 52

Figure 44: 200HP EFI Bearing Failure Pictures

Emissions Testing Results

As a result of the engine failure, a complete set of emissions data was not collected on the 200 EFI. However, 

conclusions can be drawn from the data that were collected. Figure 45 shows a summary of HC+NOx results from the 

emissions test on both engines. As Figure 45 shows, there was more variability in the E0 engine than on the E15 

engine. E15 fuel did not have a detrimental effect on emissions degradation on this engine family. It is worth noting that 

of the roughly 120 g/kw-hr of HC+NOx, the NOx contribution is approximately 2 g/kw-hr. Since the HC is roughly 98% of 

the total HC+NOx, graphs depicting the changes in the individual constituents were left out of this report. The relative 

enleanment from the E15 fuel did slightly increase the NOx emissions, but that was not significant in comparison with 

the HC contribution.

The CO emission results from the 200 EFI engines are shown in Figure 46. The E15 fuel resulted in lower CO 

emissions, as expected due to the relative enleanment from the difference in fuel chemistry. Both engines and both 

fuels showed the same trend of increasing CO with more endurance time.

Remaining Pieces from Cyl 3 Rod Bearing Cage

Undamaged Rod Rod from Cyl 3

Undamaged 

Bearing
Page 44 of 52

Figure 45: 200HP Two-Stroke HC+NOx Emission Results Summary

Figure 46: 200HP Two-Stroke CO Emission Results Summary

Average HC+NOx Emissions Output: 200 EFI 2 Stroke

EEE and E15 Fuel

110

112

114

116

118

120

122

124

126

-30 0 30 60 90 120 150 180 210 240 270 300 330

Endurance Time [Hours]

Emissions [g/kw-hr]

E0 Engine, EEE Fuel E15 Engine, EEE Fuel E15 Engine, E15 Fuel

Average CO Emissions Output: 200 EFI 2 Stroke

EEE and E15 Fuel

110

160

210

260

310

360

410

-30 0 30 60 90 120 150 180 210 240 270 300 330

Endurance Time [Hours]

Emissions [g/kw-hr]

E0 Engine, EEE Fuel E15 Engine, EEE Fuel E15 Engine, E15 Fuel
Page 45 of 52

Engine Performance Comparison

The power and torque data (corrected per ISO 3046-1) from the E0 200HP EFI engine are shown in Figure 47. There 

were slight differences in the curves, but the changes from zero hours to 300 hours were less than 1% for both peak 

torque and peak power.

Figure 47: E0 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 Fuel

Data for the E15 engine on both EEE-E0 fuel and E15 fuel are shown in Figure 48. A comparison of the output at the 

zero hour and 150 hour checks are included. Similar to the E0 engine, there was less than a 1% change from the zero 

hour check to the 150 hour check for both the peak torque and peak horsepower for either fuel. There was an increase 

of approximately 2% in both peak torque and peak power when changing from E0 to E15 fuel. The engine may have 

been operating in a range closer to the Lean Best Torque on the E15 fuel due to the enleanment from the fuel change 

and/or the volumetric efficiency may have been better due to the additional charge cooling of the ethanol fraction. Figure 

49 shows the difference in exhaust gas temperatures during the same power runs on the 2 different fuels. Since this 

was a 6 cylinder engine and individual cylinder measurements were possible, the average and maximum changes in 

EGT were plotted for clarity. On average use of the E15 fuel resulted in a 15-20°C increase in EGT in the range of 

frequent steady-state operation (>4500 RPM). The maximum increase in EGT for any individual cylinder when using 

E15 was 28°C.

Normalized Power and Torque Output

E0 Engine on E0-EEE Fuel, 200HP EFI 2 Stroke 1B810060

0.7

0.75

0.8

0.85

0.9

0.95

1

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Engine Speed

Normalized Torque

0.7

0.75

0.8

0.85

0.9

0.95

1

Normalized Power

Zero Hour Torque Midpoint Torque Endpoint Torque

Zero Hour Power Midpoint Power Endpoint Power
Page 46 of 52

Figure 48: E15 Engine Power and Torque Output at Endurance Check Intervals-EEE-E0 and E15 Fuel

Figure 49: E15 Engine-Exhaust Gas Temperature Change at Wide Open Throttle, EEE-E0 to E15 Fuel

Normalized Power and Torque Output

E15 Engine Summary, 200HP EFI 2 Stroke 1B810061

0.7

0.75

0.8

0.85

0.9

0.95

1

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Normalized Engine Speed

Normalized Torque

0.7

0.75

0.8

0.85

0.9

0.95

1

Normalized Power

0 Hour E0 Torque 150 Hour E0 Torque

0 Hour E15 Torque 150 Hour E15 Torque

0 Hour E0 Power 150 Hour E0 Power

0 Hour E15 Power 150 Hour E15 Power

Engine Composite Change in Exhaust Gas Temperature due to 

E15 Usage, 200 EFI Two-Stroke, WOT, 1B810061 

0

5

10

15

20

25

30

2000 2500 3000 3500 4000 4500 5000 5500 6000

Engine Speed (RPM)

EGT Change (°C)

Average EGT Increase Maximum EGT Increase
Page 47 of 52

End of Test Teardown and Inspection

As was the case for the other engine families, the main areas of focus during teardown were looking for signs of wear 

and also material compatibility issues. Visual inspection of the components of the 2 engines did not suggest significant 

differences between them (aside from the rod bearing failure). In particular, the bore finish, carbon deposits, bearings 

from the small and big end of the rod, and main bearings were inspected for signs of mechanical or thermal distress and 

accelerated wear. No significant differences were noted aside from slight differences in the appearance of the wrist pins, 

as shown in Figure 50. 

Figure 50: Cylinder 2 Wrist Pin Comparison, E0 on Left, E15 on Right

To provide a more in-depth analysis, selected components were further inspected. Using the same techniques as 

applied to the 9.9HP four-stroke components, the pistons and wrist pins from cylinder 2 on the 200HP EFI two-stroke 

engines were checked for material hardness. The results can be seen in Table 5. There were no significant differences 

in the hardness between the wrist pins, but there was a slight difference in hardness of the pistons (6.3%). The lower 

hardness of the piston on the E15 engine suggested it may have been running at higher temperatures. The nature of 

two-stroke engines causes them to be very sensitive to piston fit/piston temperature. An increase in piston temperature 

caused by fuel differences could cause increased propensity for power cylinder failures for customers. The slight 

difference in hardness was near the limit of repeatability for the test method so the results should be considered an 

indicator only. More testing would be necessary to gain confidence with a statistically significant sample size. 

Table 5: Hardness Measurements on Various 200HP EFI Two-Stroke Engine Components

2.5L 200HP EFI

Hardness 

Scale

E0

1B860010

E15

1B810061

Percent 

Difference

Piston Wrist Pin, Cyl 2 Rc 54.7 54.1 1.1%

Piston Crown, Cyl 2 BHN 63.0 59.0 6.3%

In addition, the high pressure fuel pumps from both engines were sent to the pump manufacturer for flow testing. There 

were no significant differences in pump output between the 2 pumps, and they were within expected flow ranges for end 

of life components.
Page 48 of 52

Additional Testing

4.3L V6 Catalyzed Sterndrive Emissions Comparison

Since the E15 fuel and a catalyzed engine were both readily available in the test lab, additional testing was performed

beyond the test program requirements. Emissions tests were performed on E0-EEE fuel and E15 test fuel to determine 

any immediate impacts of increased ethanol for this engine family. No durability testing was performed. The 4.3L V6 

sterndrive engine (General Motors V6 that was adapted and modified for marine use) was equipped with closed-loop 

electronic fuel injection and exhaust catalysts. The standard calibration for this engine in Mode 1 operation (rated speed 

and power) was such that the engine ran rich of stoichiometric to control exhaust gas temperatures. This is a common 

engine control approach to protect components during high power operation. For the type of exhaust gas oxygen 

sensor used on this engine, rich operation allows for no feedback control of the fuel air mixture. As such, the engine ran

open-loop at Mode 1. All other modes ran closed-loop. The 5 mode HC+NOx and CO emissions totals were lower on 

E15 fuel due to the fact that the engine ran approximately 4.5% leaner on the E15 fuel at Mode 1. The HC+NOx at 

Mode 1 changed from 1.18 g/kw-hr on EEE to 1.10 g/kw-hr on E15. This small reduction was driven by the reduction of 

HC emissions. The NOx emissions increased on E15, but not as much as the HC decreased, yielding an overall lower 

total. The CO at Mode 1 was reduced from 45.6 g/kw-hr on EEE to 29.8 g/kw-hr on E15. The reduction of CO was 

attributed to the leaner operation at Mode 1. The HC+NOx and CO values for the remainder of the mode points were

essentially the same since the closed loop fuel control allowed the engine to run at the same equivalence ratio. See 

Figure 51 for details of the emissions outputs.

The leaner operation at wide open throttle (Mode 1) caused an increase in exhaust gas temperatures when operating on 

E15 fuel. The exhaust gas temperature increase across all 6 cylinders was approximately 20°C. The elevated EGT

during WOT operation could cause valvetrain durability issues. The catalyst temperatures were approximately 32°C

higher at Mode 1 with E15 fuel. This increase in catalyst temperature at WOT would likely cause more rapid 

deterioration of the catalyst system leading to higher exhaust emissions over the lifetime of the engine. The full impact 

of E15 on catalyst life would depend on the duty cycle of this engine in actual application. Typical duty cycles of marine 

engines include considerable amounts of time at WOT operation (open loop) so the catalyst temperature increase is of 

concern.
Page 49 of 52

Figure 51: Emissions Comparison 4.3L V6 Catalyst Sterndrive, EEE vs. E15

The other aspect that was affected by running E15 on the closed-loop controlled engine was the fuel consumption. 

Since the closed-loop control system drove to an equivalence ratio, the fuel flow rate increased to account for the 

differences in fuel chemistry. Table 6 shows the fuel flow measurements by mode point along with the percent 

difference in fuel flow between the 2 fuels (positive values mean E15 fuel flow is higher). In closed-loop operation, the 

fuel flow increased 5.3% on average on E15 fuel. This increase in fuel flow causes concerns not just in fuel mileage, but 

also in useful range of the craft.

Table 6: Fuel Flow Comparison on 4.3L V6 Catalyst Sterndrive, EEE vs. E15

EEE E15

Mode Fuel Flow Fuel Flow Difference

kg/hr kg/hr %

1 46.8 47.0 0.4%

2 24.2 25.5 5.3%

3 13.1 13.7 4.7%

4 7.1 7.5 5.2%

5 2.0 2.1 5.9%

Mode 2-4 Average 5.3%

0 1 2 3 4 5 6

Mode Point [-]

HC+NOx [wsg/kw-h]

0.0

0.5

1.0

1.5

CO [wsg/kw-h]

0

30

60

E0-EEE Fuel

E15 Fuel

HC+NOx

CO

4.3L V6 Catalyst Sterndrive Emissions Comparison

EEE vs. E15 Fuels
Page 50 of 52

Final Summary

Summary of Results:

EPA’s recent announcement of a partial waiver approving E15 fuel for use in 2001 and newer cars and light trucks9 will 

create an opportunity for consumers to misfuel their marine engines. This program indicates that misfueling currently 

available marine outboard engines may cause a variety of issues for outboard engine owners. These issues included 

driveability, materials compatibility, increased emissions, and long-term durability. There were also 2 examples of how 

the ethanol fuel caused an increase in fuel consumption.

9.9HP Carbureted Four-Stroke:

The E15 engine showed high variability in HC emissions at idle during the emissions tests at the end of the 300 hour 

endurance period. Both the E0 control engine and E15 test engine ran leaner at idle and low speed at the end of the 

endurance test. When operated on E15 fuel after 300 hours of endurance, the lean operation at idle coupled with the 

additional enleanment from the E15 fuel caused the engine to exhibit misfire and poor run quality (intermittent misfire or 

partial combustion events). A misfiring engine would cause customer dissatisfaction due to the inability to idle the 

engine properly, excessive shaking, and hesitation or possibly stalling upon acceleration. As it relates to this study, the 

misfire caused an increase in HC emissions at idle. This increase in HC variability at idle caused the average total 

HC+NOx to increase from the start to end of endurance, whereas the HC+NOx on E0 fuel on both engines showed a 

decreasing trend. As expected, the CO emissions were reduced when using E15 fuel due to the leaner operation.

The power and torque output of the E15 engine was higher with E15 fuel than with E0 fuel. The power and torque 

output of the E0 control engine increased slightly with more endurance time. The power and torque output of the E15 

test engine showed a flat or declining trend with more endurance time.

The end of test inspection showed evidence of elevated temperatures on base engine components due to the lean 

running on E15 fuel. There were significantly more carbon deposits on several components of the E15 engine, 

indicating that these parts likely had higher metal temperatures during operation. Hardness measurements indicated 

that the pistons had higher operating temperatures on the E15 engine. The exhaust gas temperature increased 17°C at 

wide open throttle as a result of the leaner operation on E15 fuel.

The fuel pump gasket on the E15 engine also showed signs of deterioration compared with the E0 engine after 

approximately 2 months of exposure to E15 fuel.

300HP Four-Stroke Supercharged Verado:

The E15 Verado failed 3 exhaust valves prior to completion of the endurance test. One valve completely failed and 2 

others had developed significant cracks. Metallurgical analysis showed that the valves developed high cycle fatigue 

cracks due to excessive metal temperatures. The majority of exhaust valves on the E15 engine lost a significant amount 

of lash which may have contributed to the observed valve failures. The exhaust gas temperature increased 25-30°C at 

wide open throttle due to the lean operation with E15 fuel.

In addition to the elevated temperatures on the exhaust valves, the pistons showed evidence of higher operating 

temperatures. The carbon deposit differences indicated that the E15 engine’s pistons were hotter during operation.

The E15 Verado generated HC+NOx values in excess of the Family Emissions Limit when operated on E15 fuel, but did 

not exceed the limit when operated on EEE-E0. The primary contributor to the increase in exhaust emissions was the 

NOx due to enleanment caused by the oxygenated fuel. The CO emissions were reduced when using E15 fuel due to 

the leaner operation, as expected.

At emissions mode point 3, the lean combustion due to the E15 fuel caused the engine to lose torque output due to 

operation significantly leaner than LBT. As a result of the torque loss, the throttle input had to be increased 10% to 

maintain the same torque output as on E0-EEE fuel. The change in throttle input caused an increase in fuel flow of 

10%. Mode 3 is representative of a typical cruising speed and load. The E15 fuel would cause the fuel consumption to 

be 10% higher at that operating point for a customer.
Page 51 of 52

200HP EFI 2.5L Two-Stroke: 

The 200HP EFI two-stroke engine showed no signs of exhaust emissions deterioration, though the emissions output 

after the full endurance testing was not measured due to a failure of the E15 engine. The primary driver of the HC+NOx 

emissions on this engine family was HC (approximately 98% of the HC+NOx total). As expected, since the E15 fuel 

caused the engine to run lean, the HC emissions were lower, as were the CO emissions. There was more variability of 

HC+NOx observed on the E0 engine than the change in emissions on the E15 engine. The deterioration of the CO 

emissions had similar trends between the 2 engines.

The endurance test of the E15 engine was stopped short of the 300 hour target due to a connecting rod bearing failure 

on cylinder 3. The root cause of the bearing failure could not be identified. More testing is necessary to understand the 

effects of ethanol on two-stroke engine lubrication mechanisms where the oil and fuel move together through the 

crankcase. The E0 engine completed the entire 300 hours of durability testing. 

Other than the bearing failure, the end of test teardown and inspection did not show any visible significant difference 

between the 2 engines. Hardness checks performed on the pistons of both engines indicate that the E15 engine may 

have had higher piston temperatures, a concern on two-stroke engines where higher temperatures could lead to more 

power cylinder failures. The exhaust gas temperature increased 15-20°C on average due to the lean operation with E15 

fuel.

4.3L V6 EFI Four-Stroke Catalyzed Sterndrive

Since E15 fuel was readily available in the test facility and an engine equipped with exhaust catalysts was on the 

dynamometer, emissions tests were conducted on a 4.3L V6 sterndrive engine. No durability testing was performed. At 

rated speed and wide open throttle the exhaust gas temperatures increased by 20°C on average and the catalyst 

temperatures increased by 30°C. This increase in catalyst temperature would likely cause more rapid aging and 

deterioration of the catalyst system at WOT. The overall effect of the increase in deterioration rate would be duty cycle 

dependent. The HC and CO values decreased at the Mode 1 (rated speed, rated power) emissions test point, which is 

an open loop operating point, due to leaner operation with E15 fuel, as expected. The fuel consumption increased by 

4.5% at the operating points that were running in closed-loop fuel control.

Recommendations:

This test program was limited in scope in terms of operating conditions. More investigation is necessary to understand 

the effects over a broader range of conditions. Ethanol’s effects on part load operation, cold start, hot restart/vapor lock, 

and overall driveability need to be evaluated. The wide range of technology available for marine engines due to the wide 

range of engine size will complicate this issue significantly. Mercury Marine produces engines from 2.5HP-1350HP with 

a wide array of technologies ranging from two-stroke or four-stroke; carbureted, EFI, or direct fuel injected; naturally 

aspirated, supercharged, or turbocharged; and more.

Ethanol’s ability to absorb water into the fuel is of paramount concern for the marine market and this issue has not been 

addressed in this test program. The contaminants that water can bring with it, potentially saltwater, can cause severe 

corrosion in fuel systems. A leak or fuel system failure could cause the engine to be inoperable and leave the vessel 

stranded, which would obviously be a major dissatisfaction to the customer. In addition, a better understanding of the 

effects higher ethanol blends have on marine fuel systems in terms of materials compatibility and corrosion is needed. 

Marine vessels tend to have very long storage durations, can be stored in very humid environments, and will have more 

opportunities to have fuel system exposure to water, including saltwater. 

More testing is needed to understand how ethanol blends affect oil dispersion in two-stroke engines that have fuel and 

oil moving through the crankcase together. Ethanol tends to be a good solvent and may break down lubrication at 

critical interfaces by cleansing these surfaces of the residual oil film. 
Page 52 of 52

References: 

1. B. Beilfuss et al, “Mercury Marine’s New High Performance 6-Cylinder Engine Family: Next Generation of 

Marine Technology”, Presented at 25.Internationales Wiener Motorensymposium (25th International Vienna 

Engine Symposium), April 29-30, 2004

2. M. Ross, “Fuel Efficiency and the Physics of Automobiles”, Contemporary Physics 38, no. 6 P 381-394, 1997.

3. ASTM Standard D86, 2010a, “Standard Test Method for Distillation of Petroleum Products at Atmospheric 

Pressure,” ASTM International, West Conshohocken, PA, 2010, DOI: 10.1520/D0086-10A, www.astm.org. 

4. ASTM Standard D2699, 2010, “Standard Test Method for Research Octane Number of Spark Ignition Engine 

Fuel,” ASTM International, West Conshohocken, PA, 2010, DOI: 10.1520/D2699-10, www.astm.org. 

5. ASTM Standard D2700, 2010, “Standard Test Method for Motor Octane Number of Spark Ignition Engine Fuel,” 

ASTM International, West Conshohocken, PA, 2010, DOI: 10.1520/D2700-10, www.astm.org. 

6. ASTM Standard D5501, 2009, “Standard Test Method for Determination of Ethanol Content of Denatured Fuel 

Ethanol by Gas Chromatography,” ASTM International, West Conshohocken, PA, 2009, DOI: 10.1520/D5501-

09, www.astm.org. 

7. ASTM Standard D5845, 2001(2006), “Standard Test Method for Determination of MTBE, ETBE, TAME, DIPE, 

Methanol, Ethanol and tert Butanol in Gasoline by Infrared Spectroscopy,” ASTM International, West 

Conshohocken, PA, 2006, DOI: 10.1520/D5845-01R06, www.astm.org. 

8. Y. Wang, Introduction to Engine Valvetrains, Copyright 2007: SAE International, Warrendale, PA. P. 553

9. “EPA Announces E15 Partial Waiver Decision.” United States Environmental Protection Agency, Office of 

Transportation and Air Quality, EPA-420-F-11-003, January 2011.