oil temperature lowers - bug?

[Guest]

Hello,why does the oil temperature lower, if you increase the thrust? Shouldn't it be vice-versa?RegardsDietmar

[Mats_J]

HiJust a shot from the hip here. I haven't noticed this myself. I was thinking the oil pumps are mechanically connected to one of the shafts. When increasing thrust i.e. increasing the revs on the shaft you also increase the oil flow through the engine. An increased flow should make for better cooling and thus a lower oil temperature.But I'm sure there's someone in this community that has the right answer to your question. ;-)Regards

[crvm]

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[Guest wkzzo]

Dont know about the GE engined 767's ,but I can tell you on the CFM56 engines on the 737NG the oil cooler is in the bypass section of the fan duct, and as N1 is increased so is airflow through the oil cooler,thus lowering oil temps.

[Guest]

That

[Mats_J]

That sounds like a more plausible reason and it sure has a bigger impact on oil temperature as well...Oh well, I've learnt something new, today as well! ;-)Regards

[Guest Ian_Riddell]

The oil is generally cooled by fuel on the CF6. There is a heat exchanger (which runs fuel pipes next to oil pipes) under the cowls, so the temperature of the oil will be affected by fuel temperature and, to a certain extent, undercowl temperature.As I understand it, the undercowl area air temperature is monitored and controlled automatically. Air is drawn into this area from the engine bypass duct (coldstream) when things start to heat up. Door(s?) open up allowing the bypass air in.Unfortunately, a lot of this stuff is controlled by non-electrical means so I know very little about it (or what oil temps to expect... specifically, whether they go up or down at high rpm). Looking at the cooling system diagrams, I'd expect them to go up, initially, with increasing rpm, then, when the undercowl cooling cuts in, the temps to stabilize or cool. However, I would expect them to rise again if the engine revs remain high. I don't think oil temps would go down because of more oil flow.... Higher rpms also mean higher oil pressures (which generate greater heat), higher engine bearing temps, etc.Looking forward to a definitive answer :-)Cheers.Ian.

[Guest HPSOV]

G'Day Ian, long time no see!You're spot on (as always). With the GE engine the oil is cooled by the fuel, thus more fuel flow equals more cooling! If you have a look at the non-normal checklist for high oil temperature you will see that you infact INCREASE thrust on the affected engine in an attempt to reduce the temperature. With P&W engines this is not the case, and you DECREASE thrust to reduce temperature. And on RR engines the checklist instructs you to move the thrust lever to a 'Mid-Range' in the event of high oil temperature. Very confusing as we operate all 3 engine types!