Originally Posted By: kschachn
I'll play my hand here and say that no one, ever, is going to convince me that you could see the difference. The heat transfer between the coolant and the block/head is where the vast majority of the cooling takes place. Besides, any cooling the oil performs has to be rejected at the pan, right? Or on some cooler interior surface (but where do you find that?)
I sort of agreed until recently, but my experiments prove otherwise.
Logically, the hottest oil in the engine is that coming out the big end bearings, second hottest the mains...these are the locations where the engine is actively working against the oil, shearing it, a couple of hundreds of watts per bearing at 3-4k RPM.
That oil drops back into the sump, having made no contact with cooled surfaces...that which does little to no work anyway, is, as you say cooled/warmed by running down water cooled/heated surfaces.
Dropping a type K thermocouple down my disptick, directly between the high/low mark, my Caprice regularly reads 105-110C,and if I run 5 minutes at 4K revs, will read 120-125c...in ambients of -2 to 5C, well above coolant temperature.
Push the thermocouple lower in the pan (Caprice has a big winged alloy pan), the oil temperature drops rapidly..an oil temperature sender closer to the pan wall will give a temperature closer to the pan temperature than what's leaving the bearings...perfect indicator of bearing supply temperature, but no correlation whatsoever on the working temperature in the bearings, which is determined by specific load, and RPM, and will be 10-20(+) C higher than the bulk oil temperatures.