Please explain the high temperature the differential oil in a RWD drive car can reach? So high in fact that in a race car the diff usually fails if the oil cooler stops working.Air cooled is a different beast and yes oil is connected to water. It heats and cools along side with water.
I found this on line: As you can see it would cause problems if the coolant reached these temperatures. As I own a diesel Cruze i know the coolant sits around 80C and my daughter's petrol 1.6T Cruze runs at over 100C.
For non-synthetic motor oil, the traditional approach is to try to hold oil temperatures between 230 and 260 degrees F. For full synthetic motor oil, maximum can exceed 300 degrees. In all cases, less than 212 will cause water buildup in the crankcase.