Corn Field Cadilac - 2/11/2015 21:36

When we came out with the DD-15 in 2007
We did some side by side tests vs same spec Series 60

DD-15 beat it by 5% same day same load etc etc, fuel SAE test .

BUT
That gap narrowed to less than 1% in winter.
Threw us for a loop.
Turns out.
The last few years of 60s have T stat in oil cooler.


The DD15 did not.
Oil was being overcooled !!!
DD-15s all have thermostats in the cooler now.

Cold oil relatively speaking takes hp to pump.

I'd leave em in.
My 2 cents

By the way, you want oil to get above boiling temp to boil off water, or you get acid forming.
Oil can be too cold.