Have a question for some of the gearheads here! I installed a secondary trans cooler in series on my 99 7.3 SD . I just made about a 3000 mile jaunt to NH and back and my average temp was about 130 deg. The highest it got was that grade on the four lane coming out of Johnson city TN and it got up to 147 deg and I was hauling my 30 ft TT behind. When she finally down shifted out of OD she was flyin up that grade at 65 mph! I have one of those dig gauges and I am sure it is hooked up right! So can it run to cool?? Thanks

Smokie

 

I have always been told 175-200 is where you want to be. I would imagine running to cool would allow the buildup of deposits due to the fluid never getting warm enough to burn them off. They may be able to confirm this in the trans forum.

 

Typically you want the temp to be about the same as the engine. It's more about keeping the seals working good as well as the oil heating up for the detergents to work. The tolerances are also set up for running at those temps as well.