Astemo Technical Information

WATER PUMPTECHNICALSUPPORT BOOK

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

CONTENTS

What is a water pump?
■ What is a water pump? .................................................. Page 01■ What is coolant? ............................................................ Page 02■ Mechanical seal ............................................................. Page 03–04■ Water pump bearing ...................................................... Page 05■ Gasket and O-ring ......................................................... Page 06

Technical support■ For safe use ................................................................... Page 07–08■ Failure symptom - Occurrence cause chart ................... Page 09–11
・ Coolant leak ...................................................................... Page 09
・ Abnormal noise ................................................................. Page 10・ Other................................................................................. Page 11■ Replacement necessity diagnostic chart ....................... Page 12

Failure example cases■ Example cases of failure................................................ Page 13–22
・ Coolant leak ...................................................................... Page 13–17
・ Abnormal noise ................................................................. Page 18–20
・ Peripheral parts ................................................................ Page 21
・ Glossary............................................................................ Page 22

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

What is a water pump?
What is a water pump?
Role
The water pump is mounted in the front of the cylinder block for the water-cooled engine, and it forcibly circulates the coolant to maintain an adequate engine temperature.

Intake manifold

Radiator

Cylinder head

Thermostat: While warm
: While cold

Blow-by control valve

Thermostat housing

HeaterThrottle chamber

Water pump
Cylinder block

Structure
Components① Hub② Body⑥③ Bearing④ Mechanical seal③①

⑤ Impeller⑥ Drain hole
⑦ Gasket

②
⑦

④
⑤

2

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-1-

What is coolant?
Role of coolant
The temperature inside the combustion chamber of the car engine can reach 2,000–3,000°C, and the coolant
works to maintain the hot engine within an appropriate temperature range.
To attain an extended period of use, prevention of corrosion, deterioration, and rust with metals and rubbers
comprising the cooling system as well as providing anti-freezing and defoaming effects are necessary.
Thermostat

HeaterFunction of each part in cooling path

Cylinder head

■ Water jacket

Radiator

Coolant path inside the engine

Radiator cap■ Radiator

Dissipates heat from coolant■ Radiator cap

Acts as a lid for coolant supply port andregulates the cooling system pressure

Manifold■ Cooling fan

Draws in air at the back of radiator■ Water pump

Cylinder block

Forcibly circulates coolant■ Thermostat

Radiator hose

Changes path and flow rate of coolant according
to coolant temperature

Cooling fan■ Radiator hose

Water pumpPath between radiator and engine

Mechanism of coolant circulation
The engine revolution is input via the water pump pulley and hub, and the centrifugal force generated by therotating impeller is transferred to the coolant flow through the volute chamber diffuser.

VoluteDiffuser■ Volute

Guides the coolant flow out of
the impeller in a fixed direction■ Diffuser

Converts the coolant velocity
energy to a pressure thatallows coolant circulation
against the cooling path
resistance

Coolant flow
W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-2-

Mechanical seal
Role
Attached to the bearing shaft and body, the mechanical seal serves to seal the gap between the rotating partand the fixed end such that coolant in the pump chamber does not leak out.

Mechanical seal assembled state
FigurePhoto

Mechanical seal

Body

Bearing

Mechanical seal composition■ Mating ring
Co-rotates with the bearing shaft
and seals coolant while sliding
against the seal ring

■ Seal ring
Seals coolant while sliding against
the mating ring

■ Spring
Provides adequate surface pressure
between the mating ring and seal ring

■ Cartridge
Fixed to the body to hold the seal
ring, spring, etc.

■ Sleeve
Fixed to the bearing shaft to holdthe mating ring
4

W/P TECHNICAL SUPPORT

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-3-

Working mechanism
When the engine is running, a fine liquid film is formed on the sliding surface (between seal and mating rings)
owing to the rotating mechanical seal.
Surface tension prevents leakage while in the liquid state. However, as sliding occurs owing to high-speed
rotation during running, the liquid temperature on the seal surface increases and vapor is generated.
Moreover, an intrusion of contaminant onto the sliding surface can weaken the surface tension, leading to apossible coolant leak.
Consequently, a very small amount of coolant may ooze out (to bearing side).
The water pump is provided with a vapor hole at the top and a drain hole at the bottom to prevent the coolant
from entering into the bearing.

Vapor holeseal ringSliding surface (Between
and mating ring)

Prevents generated vapor
from entering into the bearing.

Vapor or a small amount of coolant may
come out as the liquid film is very fine.

Coolant(LLC)

Enlarged view

Bearing
Seal ring(Fixed side)

Mating ring
(Rotating side)

Drain hole
Prevents leaked LLC fromentering into the bearing.
W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-4-

5

Water pump bearing
Role
It is a component that receives input load and transmits smooth rotation to the impeller via the pulley and hub.
The water pump bearing is equipped with two rows of multiple rolling elements, which work to collectively
receive the load of the belt, fan, fan coupling, etc. Two different types of bearing are adopted according to theextent and position of the load––one employing balls in both rows and another employing rollers in one row.
As bearings have specified receivable loads corresponding to the size, a bearing damage (causing abnormal
noise and locking) can result from excessive belt tension and excessive deflection of fan coupling.

Composition of water pumpbearing■ Shaft

Shaft also serving as the bearing inner ring

■ Outer ring

Outer ring of bearing (press-fitted into the water
pump body)■ Grease

Charged with grease for lubrication■ Rolling element (ball or roller)

Receives load by two rows of rolling elements(Two-row ball type and ball + roller type areavailable)■ Rolling element retainer

Functions to guide the rolling elements■ Lip seal (both ends)

Prevents intrusion of contaminant, moisture, etc.
from outside

Receiving load by two rows of rolling elements

Impeller side lip seal
Preventing intrusion ofvapor and fluid fromdrain chamber

Pulley side lip seal
Preventing intrusionof contaminant andfluid from outside

Any intrusion of moisture into the bearing
can cause deterioration of internal grease
and damage to the bearing (causing
abnormal noise and locking).

6

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-5-

Gasket and O-ringRole
Gasket and O-ring work to seal the water pump and mating parts from elements such as the coolant.
*Hitachi Water Pump comes with a gasket even when the water pump (genuine part) in the vehicle assembled
state employs the liquid gasket. Please use the gasket provided when replacing.

About liquid gasket (FIPG)
In the production line, stringent control on the application amount is implemented by the use of components
including an FIPG applicator.
In addition, attention is necessary for replacement because installation time constraints and the curing timeafter application must be considered.
Therefore, Hitachi Water Pump is provided with gasket to improve the work efficiency and prevent failuresassociated with liquid gasket.

(Reference)■ Liquid gasket applicator■ Example of maintenance procedures(Excerpts)
Apply seal packing (diameter of 2.2–2.5 mm) along theoutside of the water pump groove.
■ Caution ■● Degrease the mounting surface.
● Assemble within 5 min after application of seal packing.
● Do not start the engine before 2 h after installation.
Application
location■ Example case where a liquid gasket was applied to the mounting surface,and extruding liquid gasket was caught in the mechanical seal

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-6-

7

Technical support
For safe use

1

Do not use liquid gasket on the mounting surface (including
gasket and O-ring).
■ See page 06 for details.

2

Thoroughly clean the mating mounting surface (rust,
packing residue, etc.).
■ Prevents coolant leakage from the mounting surface.

3

Before replacing the pump, thoroughly clean the engine
cooling path.
Replace coolant two to three times (perform flushing)while using the old water pump to remove contaminantsfrom the coolant path, and then replace with a new waterpump.
■ Prevents coolant leakage from the mechanical seal resulting fromcontamination by foreign matter.

4

After replacing the pump, replace the coolant (LLC).
*Ensure that LLC is used at the concentration specified by
the car manufacturer (30-50%).
■ Degraded coolant (LLC) can cause various problems in the cooling system.

8

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-7-

For the coolant, do not use anything other than LLC.
(Radiator leakage inhibitor, etc.)

5■ Any substance can become a contaminant in the coolant and cause issues due
to consequent mechanical seal damage.

Ensure that the belt tension conforms to that specified by
the car manufacturer.
(Check the auto tensioner for damage.)6■ Any excess input can result in issues including failure of bearing parts (bearing
and body).

Check the bearing components (bearing, etc.) of theauxiliary parts other than the water pump for any damage
including looseness.

7■ Rattle from other auxiliary parts can propagate through the belt and generate
vibration input, affecting the bearing parts (bearing, hub, and pulley).

Check the fan coupling for any damage including looseness.
(Bearing, etc.)

8■ If there is looseness with the fan coupling, eccentricity (large deflection) resulting
from tip unbalance can lead to serious problems, such as failure of bearing parts(including the bearing and body).

！
CautionAny problem arising from water pump can hinder thedriving of the vehicle.
Please observe the instructions provided. We also
recommend regular inspections and early replacement.
W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

-8-9

Failure symptom - Occurrence cause chart
Failure symptom: Coolant leakOccurrence
location

Failure part

CASE

Mechanical seal
surface abrasion

Contaminants (e.g., dust,
sludge, and rust) existingin the coolant were caught
in the seal part, causing
damage to the sliding part.

Contaminantadhesion tomechanical seal

After an occurrence of contaminant ・ Coolant degradation
adhesion onto the sliding surface ・ Elution of members in the coolant path・ Excessive application of liquid gasket
or intrusion of elements such as
and adhesive
liquid gasket and adhesive into the・ Coolant charged before curing of liquidpump chamber, contaminant biting
gasketoccurred in the seal part, resulting ・ Contamination of the coolant by radiatorin separation.
leakage inhibitor, etc.

Cracking or burnwith mechanical seal

Operated without coolant fed
・ Operation performed while coolant
to the seal part, resulting in alevel is low (insufficient air bleeding)heat shock after the seal
・ Decrease in defoaming perforsliding surface temperaturemance due to degraded coolant
became high.

1
Fromdrain hole

CASE

2
From
mounting
surfaceO-ring tearO-ring seizure

Gasket and O-ringcracksMounting surface
fault

CASE

3
From mainbody
10

Erosion by cavitation(pitting)

Occurrence cause

Operation in abnormally high temperature environments

Insufficient tolerance temperature
Application of liquid gasket and adhesive
Hardening due to aging
Contaminant biting during mounting (insufficient cleaning)

Manufacturing defectInsufficient tightening torque with the mounting bolt
Faulty parallelism of the main body (manufacturing defect)

Acidification and decrease in defoaming
performance due to coolant degradation
Coolant amount is insufficient (insufficient air bleeding)Faulty radiator cap

CavityManufacturing defect

W/P TECHNICAL SUPPORT

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

・ Insufficient cleaning of coolant path・ Contamination of the coolant by radiatorleakage inhibitor and other elements
・ Bearing damage → Rattling →Looseness occurrence in seal parts on
same axles-9-Failure symptom: Abnormal noise
Occurrence
location

Occurrence cause

Noise type - Failure part

CASE

Croaking

1

Rumbling(Metallic noise)

Bearing
internal failure

Excessive
input frombelt

･ Excessive belt tension･ Damage to the auto tensioner･ Damage to the bearing ofauxiliary parts such as idler

Coolant intrusion into the bearing
caused by coolant leak from themechanical seal partFrombearing

Excessive vibration input due to deflectionof the hub, pulley, and fan coupling

CASE

2
From
mechanical
seal

High
frequency
noise(Peep, etc.)Lowfrequency
noise

Insufficient lubrication at the seal part due
to low LLC concentration

Surfacepolishing of
mechanicalseal(Boom)

Coolant shortage (insufficient air bleeding)resulting in occurrence of idling

Mechanical seal
carbon transfer

CASE

Excessive idling

Belt deterioration or insufficient belt tension

Sliding noise3
Frompulleyand hub

Excessive sliding surface pressure in
the seal part (set load is high)Large hub deflection
Belt alignment fault

Clatter
Rustling

Contaminant biting between pulley and hub

Loose pulley bolt or insufficient tightening torque
W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 10 -

11Other failure symptoms
Symptom
Impellerloss

Occurrence
location

Failure part

Blade

Decreased
thickness
Blade wear

Occurrence cause･ Corrosion due to coolant degradation (e.g.,
acidification and decrease in defoaming
performance) and *cavitation･ Cavitation occurrence due to faulty radiator
cap*Cavitation: See page 22

Idling ofimpeller

Crimping part

Abrasion of
impeller
crimping partPress fitting
part

Separation frombearing shaft･ Coolant degradation (acidification, decreasein defoaming performance)･ Corrosion due to faulty radiator cap anderosion by cavitation

Manufacturing defect･ Insufficient press fitting force due todimensional defect･ Slanted press fitting during assembly

Coolant freezing

BodydamageMain body

Body breakage
or damage

Excessive belt tension

Occurrence of excessive vibration input
caused by tip whirling resulting from fan
coupling damage

Pulley hub
separation

Pulley/hub
Press fitting
part

Pulley idling due
to coming off of
shaft

Excessive
input frombelt

･ Excessive belt tension･ Damage to the auto tensioner･ Damage to the bearing ofauxiliary parts such as idler

Excessive vibration input due to deflection of
the hub, pulley, and fan coupling

Belt alignment failure resulting from slanting
caused by contaminant biting between thepulley/hub and mounting surface

Manufacturing defect･ Insufficient press fitting force due todimensional defect･ Slanted press fitting during assembly

12

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 11 -

Replacement necessity diagnostic chart (coolant leak, abnormal noise)
When you suspect coolant leak or abnormal noise ...
Check the necessity for replacement according to the following sequence.

Coolant leak
AbsentCoolant leak markVisually check as-is state.

Symptomcheck

Abnormal noise
Check for abnormal noise Absent
1. Engine warm up
2. Idle operation: 10 min

Visually check withfocus on the drain holeand mounting surface.

Check the sound by
sensory evaluation.

Present

Present

Coolant pressure
test

Check the W/PUMP
mechanical seal
squeak

1. Pressurization byradiator cap tester(Pressurization at 100
kPa for 20 min)1. Set the LLC concentration to 50%.
2. Engine warm up
3. Idle operation: 10 min

Present

Check thelocation of leak.

Check the sound by
sensory evaluation.

AbsentCheck the locationof leak.

AbsentCheck each part is required

1. Engine warm up
2. Idle operation: 20 min

Improvement
to mechanicalseal squeaking

Present

Present

Rotation test

AbsentPresent

Check bearing
damage with eachpart
1. Remove the belt.
2. Manually rotate thepulley of each part.

Check for the presence ofstaggering feel and rattle.

AbsentCheck of belt squeak

Mechanicalseal squeaking

Present

1. Replace the belt or
pulley with a new one.
2. Idle operation: 10 min

Check the sound by
sensory evaluation.

W/PUMP

No problem exists withthe water pump.
Temporary coolant leakor normal vapor leak.
Continue with use.

Replace the waterpump.

Other than

W/PUMP

AbsentReplacement ofdamagedparts

No problem exists withthe water pump.
Continue with use.

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 12 -

13

Failure example cases
Coolant leak
Coolant staining
Coolant circulates in the engine, and naturally becomes dirty as the operating time accumulates. For
this reason, a periodic replacement is necessary as regular maintenance. However, when replacing
the pump, it is additionally required to perform thorough cleaning and replace the entire volume ofcoolant with new one.
･ If cleaning is not sufficient or the coolant is not replaced in its entirety, contaminants such as dust,
sludge, and sand in the coolant path can be caught onto the mechanical seal sliding surface (sealsurface), and coolant may leak from the drain hole resulting from a loss of sealing performance.

(1) Coolant contamination
Installed period: 3 days
Mating ring part (rotating side)

Seal ring part (fixed side)

Coolant degraded owing to contamination

Travel distance: 5,000 km

Coolant degraded owing to contamination(2) Contaminant biting in mechanical seal
Installed period: 3 months

Contaminant biting
14

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 13 -

(3) Contaminant biting in mechanical seal
Travel distance: 42 km

Contaminant biting

Travel distance: 2,352 km

Circular scars caused by contaminant biting(4) Burn and cracking of mating ring(5) Other (charging of leakage inhibitor)

Travel distance: 8,189 km

Travel distance: 10,000 km

Burn and cracking occurred because
operation was performed while lacking
coolant after coolant level became low.

Adhesion of the leakage inhibitor
to the pump chamber

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 14 -

15

Coolant leak and overheating
Coolant degradation
Oxidation and concentration dilution occur with the coolant as the use time extends, causing advancing
of degradation. Although the anti-freezing performance hardly changes over time, decreases occur withthe anti-rust and defoaming performances. As a result:･ Metal corrosion can generate biting contaminants, such as rust, in the mechanical seal sliding surface(seal surface), ultimately causing coolant leak from the drain hole.
･ Propagation of metal corrosion and *cavitation can lead to coolant leak resulting from pitting as wellas to overheating resulting from a loss of impeller.
*Cavitation: See page 22
Ensure that the coolant concentration (30-50%) is appropriate for the climate of the region where theproduct is used.

(1) Rust biting in mechanical seal
Travel distance: 42 km(2) Pitting in the body (through the hole reaching
the drain hole and resulting in coolant leak)
Travel distance: 9,000 km

Occurrence of erosion by cavitation

Drain hole(3) Pitting in the plug

Occurrence of erosion by cavitation

Plug
16

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 15 -

(4) Rust occurrence with the impeller

Occurrence of corrosion and rust

Travel distance: 7,646 km

Installed period: 12 months(5) Impeller corrosion and loss Occurrence of erosion by corrosion and cavitation
Installed period: 6 months

Installed period: 12 months

W/P TECHNICAL SUPPORT

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 16 -

17

Coolant leak
Liquid gasket application failure
It is difficult to apply an appropriate amount of liquid gasket uniformly by hand, and as a result:･ Sealing performance of mounting surface can become inconsistent, and coolant may leak fromthe mounting surface.
･ The liquid gasket protruding inside the pump chamber can fall and be caught in the mechanicalseal sliding surface (seal surface), leading to coolant leak from the drain hole.
In addition, as the liquid gasket requires to be left approximately for 2 h after installation for drying
without charging the coolant, it is recommended, considering the work efficiency, to perform mounting
with only the gasket provided.
*When liquid gasket is used with the O-ring specification, the original sealing performance may not be attained,
and coolant leak can result.

(1) Liquid gasket application failure (Application of liquid packing is not necessary)...See page 06
Combined use of liquid gasket andgasket specification

Combined use of the liquidgasket and O-ring specification(2) Case example of liquid gasket biting into mechanical seal
Travel distance: 0 km

(3) Liquid gasket residue caught in mechanical seal
Travel distance: 284 km

18

W/P TECHNICAL SUPPORT

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 17 -

Abnormal noise, seal squeaking (high-frequency noise, low-frequency noise)
Stick-slip occurrence
Seal squeaking with mechanical seal is a phenomenon in which self-excited vibration caused bystick-slip between sliding surfaces (seal surface) becomes the source of noise. Stick-slip is caused bychanges in sliding surface properties (e.g., carbon transfer, surface polishing, and uneven contact)occurring because of factors such as the starting of the engine in dry state (i.e., no coolant in the pumpchamber), degraded coolant, and poor lubrication due to low concentration.
Stick-slip: A phenomenon in which the sliding surface repeats sticking (seizure) and slipping(slide)––the same in principle as the chattering noise occurrence with wipers. )(1) Carbon transfer onto sliding surface Components of the seal ring (fixed side) transferred
Travel distance: 0 km

to mating ring (rotating side)

Carbon transfer(2) Surface polishing of sliding surface Surface polishing of the seal ring (fixed side)
Travel distance: 0 km

occurred due to seal surface lubrication fault, etc.

Surface polishing(3) Uneven contact of sliding surface Increase in surface pressure occurred at a seal surface
Travel distance: 0 km

portion due to seal surface lubrication fault, etc.

Uneven contact
W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 18 -

19

Abnormal noise (e.g., rumbling noise and croaking noise)
Bearing damage
Damage to the bearings will generate abnormal noise (e.g., rumbling noise and croaking noise).
Possible causes for bearing damage:･ Coolant leak ⇒ Coolant intrusion into bearing ⇒ Degradation of bearing grease･ Excess belt tension･ Excessive vibration and other unfavorable responses due to fastening failure with mating part,
deflection, or unbalance. As a result of excessive vibration, *fretting wear occurs to the contact
surface and fastening parts (characterized by occurrence of cocoa-colored rust).

*Fretting: See page 22(1) Bearing damage (coolant intrusion into bearing)
Installed period: 8 months

Installed period: 12 months(2) Bearing damage (fretting wear on hub surface and hub axle)
Installed period: 2 months

Hub surface

Hub axle

Travel distance: 5,149 km

20

Travel distance: 9,750 km

W/P TECHNICAL SUPPORT

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 19 -

(3) Bearing damage (burns to shaft and ball)
Travel distance: 5,000 km

Fretting wear on hub surface

Shaft

Burn mark on hub side rollingsurface
Ball

Burn mark on hub side ball

Installed period: 6 months
Trace of excessive load in belt tension direction

Body inner periphery

Bearing outer ring

Exfoliation on hub side rolling surface

Shaft

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 20 -

21

Defects associated with peripheral parts
Fan couplingWith the type in which the fan coupling is mounted at the water pump leading end, it is necessary toverify the occurrence of any problem in the coupling bearing.
･ If staggering or sticking is recognized with the rotation of coupling bearing, or if there is damage tothe bearing seal, replacement is required.
･ Even when there is no abnormality, we recommend replacing the coupling if the travel distance of
100,000 km is exceeded.
If the use of a defective part is continued, excessive vibration by whirling can damage the pump.

(1) Body damage
Travel distance: 98 km
Installed coupling(2) Bearing shaft breakage
Installed period: 9 months

22

Installed coupling

W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 21 -

Glossary
LLC (long life coolant) For its roles, see page 01.
The main component of "LLC" is "ethylene glycol (structural formula: HO-CH2-CH2-OH)", and byadding rust preventive additives for various metals (iron-, aluminum-, and copper-series), the use lifeof the coolant is extended with additional capabilities, including rust prevention, oxidation prevention,and defoaming performance, provided in conjunction with the anti-freezing effect of ethylene glycol.
Although the anti-freezing effect of ethylene glycol does not reduce, a periodic replacement is required
because degradation occurs with additives.
Raw material

EffectDegradation mode

Symptoms associated with degradation

Ethylene glycol

Anti-freezing effectPractically no degradation over time---

Rust prevention with various metals
Additive

Antioxidation effectCorrosion and rusting of each metal
Wearing by thermal load

Defoaming effectCorrosion and rusting of each metal
Cavitation occurrence

What is cavitation?
❶It is a phenomenon caused by bubbles formed in the fluid, and by the process of pressure changes
occurring in bubbles generated by the fluid flow. ❷The bubble size changes corresponding to changes

in pressure, which alters the volume of gas. The bubble goes through a process of gradually becoming
smaller according to the pressure while repeatedly expanding and shrinking.❸A bubble near a hard
face, such as that of a propeller, sticks to the surface owing to viscosity and surface tension. Then, thesurface of a bubble on the opposite side of the hard face starts sinking.❹When the bubble breaks as aresult of crashing into the surface with a jetting force, erosion is caused by the jet stream.
Image

❶

❷

❸

Marine propeller eroded by cavitation❹

What is fretting?
When there are repeated load applications to the fitting parts of mechanical elements such as railway
car axle and turbine blades, or to the contacting areas between materials, a minute relative reciprocating
slide movement occurs, leading to a surface damage, which produces reddish-brown abrasion powder,called fretting wear.
Furthermore, under continuous and repeated loading conditions, fatigue fracture can occur andpropagate from the surface damage area, significantly reducing the fatigue strength of materials. Suchfatigue phenomenon involving fretting on the contact surfaces is referred to as the fretting fatigue.
Between hub surface
and pulley

Between mounting bolt
and hub thread

Fretting wear refers to the vibration wear that
occurs when a contact load is applied between
members by vibration or other reasons.
*The abrasion powder has a characteristic cocoa
color (rust color).
W/P TECHNICAL

https://aftermarket.hitachiastemo.com/
Astemo Technical Information #019 / Updated: 2022/Feb/3, Issued: 2022/Feb/3© Hitachi Astemo, Ltd. 2022. All rights reserved.

- 22 -

23