Oil Temp

[bobcowan]

As said above, in routine street driving, oil temp will be around 10-15* hotter than water temp. Oil is mostly heated by RPM's. Situations that require extended high RPM's will heat the oil more; like road racing.

Finding the optimal operating temp is difficult, and seems to be a big trade secret. From what I've been able to find, 200* seems to be about right. Which really means that unless you're road racing, you don't need a cooler.

Max temp depends on the type oil, and duration. Cheap wally-world oil can stand 250* for a short while. A true PAO synthetic can handle 250* all day long.

There is a common myth that water will not evaporate at temps <212*F (100*C). If that were true, your kitchen floor would never be dry. Water will evaporate at anything above ambient temp/humidity. The oil in your DD probably never see's 100*C. Do a UOA, and you won't find water. My diesel truck generally runs about 175* (coolant) or so; there's no water in the oil.