The context here is what is the required temperature range of a sealant used for any oil leaks.
I think the two temperatures must be the same – because the oil flows all around the crankcase, via various galleries, to the bearings etc.
There may be internal hot spots e.g. near the main bearings, but the crankcase joint can’t be significantly hotter than the oil temperature, IMHO.
Also the EDM700 oil temp probe screws right into the end of a gallery
What you are asking makes no sense in thermodynamics terms. Oil is heated and cooled. It is cooled in large terms by the crankcase. Obviously they cannot have the same temperature, or the oil (and crankcase) would heat up until they melt and burn. With an external oil cooler, the whole thing gets even more complex, and the oil will both cool and heat the crankcase depending on spice and time.
But in very rough terms, I guess yes. But the accuracy of that answer is so low, that it may be useless in the context you are asking? This would mean your sealant have to withstand the highest temperature the oil will ever have, so that is what you chose.
Here is the proof of my original hypothesis – top of the crankcase
88C is 190F which is only slightly above my recorded oil temp of 175F.
After 65hrs, all kinds of power settings from 100% down to about 40% at FL190:
I think the position of your temperature sensors would be subject to a lot of cooling air inside the cowling.
I think those stickers are well under the boundary layer.
In what way is the temperature of the crankcase important? You want to know your oil temperature and keep it high enough to boil off the water, keep the CHTs low enough to be safe. EGTs absolute temps are unimportant, just the relative value to peak matters.
The reason I wanted to determine the crankcase temperature was because we had an oil leak which looked like it was coming from the crankcase seal, and I was looking for sealants which might work.
In the end, after some work, it turned out to be a pushrod shroud seal which was leaking, but only in flight, which made it a real bugger to track down. On the ground it would not leak at all, even with NDT developer applied to the engine to help show it up.
It was just bad luck… the one seal, worth £2. We changed both #5 pushrod shrouds and all four seals. Total parts cost £50, plus 2hrs’ labour.
I did however apply some Loctite EA9492 which is a very high temp (well, for an epoxy) resin, to the suspected area.
We also had some low level seapage through some crankcase bolts, and these were sorted by using o-ring seals. That is already used on the big through-bolts. Parallel threads are not liquid-tight so if any oil reaches the shank, it will come out through the nut.
This post also refers.
A final data point after some 100hrs of operation, including flying around Greece
Don’t ask why the “93” is still white