Originally Posted by Bluepill
FWIW, a transmission tech told me he likes to see the temps get a bit above 212 from time to time. That is hot enough to boil out any moisture that has gotten into the fluid. The trans will "breathe" a bit as it cycles from cold to warm, and that can bring in humid air.
160-180 is warm enough to cook off any moisture, it just takes longer than if it was at 212. If the truck is ran almost everyday moisture is not an issue. My Yukon sees temps to only 165 or so. So in your mechanics theory it should have 5 years worth of moisture in it. I assure you it doesn't.
Just putting this out there so no one gets worried their Trans is too cold.
Now, where his theory holds true is in motor oil of piston engines in fixed wing aircraft. But that's another story.