just courious.. why did they choose 210 deg. as the temp to run at. do diesels need the extra heat to function properly. not for nothing, my truck runs a lot better around the 180 range. can you change the thermostats to cool it off a little, or is this a bad thing. back in the day of gassers we would run at 160 and make all kinds of power.

Try 180 deg. thermostats instead of 190's.

Dont run it cooler than 180. The ECM wont even access the "warmed up" timing tables until 165-170 or so. The dmax is not a gasser from the 1960's ;) :)

cool, thanks. where can i get them...

I would Leave the thermostat like it is IMO. The engine is not running 210 even though the factory guage says it is. The engine runs 180-195. This is a perfectly acceptable range and you will not see any gains by going to a different t-stat. Like I said, not much previously accepted engine practices can be applied to the duramax. ;)

my truck always runs 178-188* acording to efi live logs have not figure out how to cal the dash guages which is 15-25* higher than actual on my truck

my efi says 199 and the gauge says 210. while it's warming up it runs all around better. even the motor noise is less.

my efi says 199 and the gauge says 210. while it's warming up it runs all around better. even the motor noise is less.

Thats because its using the 'cold' timing tables. Having a lot of timing on a cold engine is bad, so until its warmed up, it decreases timing. Decreasing timing makes EGT's go up and less power. The truck probably "feels" like it runs better because its making less noise.

If you are dead set on changing the t-stats, go ahead, but you are spending money on nothing that will gain you anything. :) ;)

When coolant temp reaches 180 deg F., the Primary, (front), thermostat starts to open, and is full open at 203 deg F.
When coolant temp reaches 185 deg F., the Secondary, (rear), thermostat starts to open, and is full open at 212 deg F.
Info from 2002 Helms. page 6-1590.

Thats because its using the 'cold' timing tables. Having a lot of timing on a cold engine is bad, so until its warmed up, it decreases timing. Decreasing timing makes EGT's go up and less power. The truck probably "feels" like it runs better because its making less noise.

If you are dead set on changing the t-stats, go ahead, but you are spending money on nothing that will gain you anything. :) ;)

so what temp does it change programs at, and what damage will it cause to run it coloer than factory 200 deg. i have heard it before about the diesel needing to warm up but never really knew why its so critical. maybe you could explain. thanks, Ray

Mine almost always runs right at 185* on the factory guage. It got up to about 200* today, that's kinda what caught my eye about this thread. I know it's well within limits, but my truck usually doesn't run that high. It will stay under 180* in the winter for quite a while.

so what temp does it change programs at, and what damage will it cause to run it coloer than factory 200 deg. i have heard it before about the diesel needing to warm up but never really knew why its so critical. maybe you could explain. thanks, Ray


Because we don't have spark plugs.