Date: 201305
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Lubrication Oil
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Not long after level off at cruise altitude I noticed the Oil Temp on the #2 Engine was highlighted in an amber box.  I pointed that out to the Captain and called for the Engine Oil Temp High checklist.  Captain pulled the QRH and started following the Engine Oil Over-temperature checklist.  As we followed the instructions in the checklist we were able to bring the oil temp back in the green range and soon after get it to stay green and go down to normal levels.  In the process of dealing with this abnormal indication Captain contacted Dispatch and Maintenance Control and discussed the situation with both.  With the oil temperature in the green and getting progressively cooler we elected to continue to our destination.  Soon oil temp was below 100 degrees Fahrenheit and stayed there for the remaining 2 hours of our flight.Still have no idea what was the cause of the high oil temp indication so I can't offer suggestions on how to prevent that from happening.  However; both I and the Captain noticed some ambiguity in the checklist we ran and lack of clarity in the Power Plant limitations section of the AOM.  Improving those two sources of written guidance will make it easier for crews to deal with similar abnormalities in the future.  Specifically: QRH -  Engine Oil Over-temperature checklist - Step 6 reads: 'If engine parameters BECOME ABNORMAL (emphasis added) or exceed operating limits; go to Engine Shutdown Procedure.' - Well; engine parameters were already abnormal; that is why we came to this checklist to begin with; and they still are abnormal (in the step above we answered 'YES' to 'Does the Oil Over-temperature condition persist?')... It seems like per the checklist one should always have to shut the engine down at this point due to abnormal engine parameters; but is that really the intent of step 6?  If so; then let's simplify the wording in it.  AOM - Power Plant Limitations - Under 'Oil temperature' it indicates TRANSIENT Oil Temperature has a maximum of 163 degrees Celsius; with a note that 'Transient operation above 155 Celsius is limited to 15 minutes.'  The term 'Transient' can be interpreted in quite a few ways and in the heat of the moment this interpretation can lead to confusion - can we either define 'Transient' or have a different and more objective measure?  Consider following hypothetical example (did not happen to us tonight) - if the Oil Temp goes to 158 Celsius and it stays there for about 45 sec; then goes back to the green range (below 155 Celsius) - that is certainly not 'Continuous' right?  It is transient with no doubt.  But what if that event is repeated every 30 minutes or so?  Say it happens 3 times over the course of a 1.5 hour flight.  Are those 3 separate events of transient high temps; or are they a 90 minute period of transiently exceeding 155 Celsius?  If we chose the second interpretation; then per the checklist we would be required to shut the engine down.  Or what if the temp was 158 Celsius for 5 minutes; then it dropped down in the green range and stayed there for 7 minutes; then went back up to 158 Celsius and hovered there again for about 5 minutes; then it went back to the green range - Is that 'Transient' or 'Continuous'?  If we call it 'Transient'; did we exceed the 15 minute limit for operating above 155 Celsius or not? The amber 158 Celsius was never on for more than 5 minutes; but from when it first showed amber to when it last was amber has been 17 minutes.




Synopsis: EMB-170 First Officer experiences high engine oil temperature shortly after level off in cruise.  The QRH is consulted and the oil temperature is brought back to within limits.  Flight continues to destination.