[gumby79]

Forgive my old no computer truck '91 Dodge Cummings
I was told by previous owner that the thermostat had ben reduced to a 175° for better FE. (See fancluch )
So iwas thinking of going back to stock185°or higher, however , last week. I was stuck in. 20-30M.p.h. traffic on tehacapi pass westbound between backer and tehacapi 105°ambient ac on.FE was down almost 5mpg because the mechanical thermal clutch was running the hole time. Ok some specs
Normal. Northwest. 40-75°f
Warming to 175° pop gos the thermostat drops th 165° and stays +-5° fan no engagement. Long steep grades ive seen as high as185°f empty

Hot weather Las Vegas 100-115°f
Warming to 175° pop downto 165°-(192 with ac) it will cycle with road speed. And fan cycle
Temp read with digital gauge
Fan cycle
Locked in at181°released at172°f

So conclusion. Increase thermostat to 185°will KILL my FE. Because the fan come on 5°befor the thermostat pops
Fan in lockup pulls about 15hp

If i spend $4-500on electronic fans. Plus controller. (To solve macanical fan hp draw) how hot will my Cummings be happy ?210°with 250°peek? (Will require a waterless. Coolant!!!) what kind of FE %increase canbe experienced? $500÷mpg gained =yearsto payoff?
as for trans I'll probably have ro take out the 3rd stock trans cooler. As it is coolant/to liquid (simaler to the one in the radiator)but on the frame under the exost manifold