Who changed the IR gun reading from F to C between measurements?
I'm being only partly facetious... Check the IR gun for consistency
Seriously...
I assume there are no actual engine oil temp gauges on the helms or in the engine rooms.
An external IR reading to get oil temp is not reliable at all as an actual temp of the oil HOWEVER, I agree that if you are taking a reading at the same spot on two engines that are both showing approximately the same coolant temp, and have been running for the same length of time under the same load, one would expect the temps in the spot in question to be similar.
Frankly, for the oil temp to be as low as indicated in the cooler measurement seems almost impossible with both engines at the same temp/load/running time.
Obviously, as mentioned, if there are oil coolers, they may require servicing. Also as mentioned, if the filters are at different distances from the engine they may show different temps for that reason.
To compare temps, the IR gun must shoot the exact same spot, at the same distance and same angle for both engines. If it was convenient to get close to one but shoot the other from several feet, there could be dramatic differences. If there is a laser pointer, remember that the temp reading is NOT at the laser dot. The laser dot shows the center (hopefully, if it is accurately made/aligned) of the "measurement cone". The further away, the wider the cone and the more of the adjacent or background surface temp is included in the measurement. For example, if half the cone is on an item that is 200F and the other half of the cone is on an item that is 100F, the temp displayed will be something between the two.
OK...FWIW, The purpose of the check of the oil filter temp would only be as a comparison between the engines for "general awareness" because if you told me that the oil temps were as described, I'd be looking for an engine cooling problem (too low) because even the high one is too low. However, based on where it was measured, it IS likely that the actual oil temp in the engine on the high one is in a reasonable range...around 220F would be good. But the other is much too low - so low as to make me question the IR gun or a difference in how they filters were "shot."
To be honest, an oil temp check like that is not a "normal" kind of diagnostic and I wouldn't personally do that sort of test. The only accurate way to measure coolant or oil temps is with a sensor mounted in the coolant/oil flow in the engine. Under any normal operating conditions, if the engine coolant temp is within spec, the oil temp will follow. IOW, in my view, you have found a "problem" that didn't need to be looked for!
But now it has to be dealt with in some way since it is part of the survey.
But, since you have the disparate readings, I'd probably do this: Start the engines and, if you can go out, run them under the same load, until they are at operating temp THEN...shoot the oil pans at the same spot I suspect your temps will be pretty close. THEN shoot those filters again, BUT just for grins.. because it doesn't matter what they show!
