Guys,

I have run into an issue that I now believe is a huge issue.

Symptom: When driving to Montana at christmas I noticed the truck was going into high idle at every fill up. Then on one pass I noticed the truck was at normal op temp going up the grade, but coming down the other side the temp dropped to the 130-140s. The temps then were -10 to -20, but I noticed recently that it will not come to op temp unless I am running down the road.

Fluids look good, no issues with overheating, but seems to take forever for it to come to op temp.

I am thinking maybe a thermostat issue?

 

No problem, that is normal operation for these trucks. The cooling systems in these trucks are enormous and designed to keep them cool while hauling large weights. Plus a diesel engine is very cool at idle and low load conditions. The engine will high idle when certain temp conditions are met. Mine has even done it here in SC after a 1/2 hour interstate drive, stop and the high idle kicks in. If you want better cold weather operation / more heat faster, get a winter front for it.

 

I live in Montana and I can tell you that it's normal for the truck to high idle any time the temp is below 39F.

And you might need a winter front running those cold temps. Especially off the pedal. No fuel means no heat.

My truck will seldom come up to operating temp unless it's rolling along in 5th or 6th. Even now when it's pushing 60f. It will always cool down if I let it idle, which I don't.

I'm thinking you don't have a problem.

 

The only thing that truely concerned me was that every hill i went down, we would go right back to 130-140 and start to lose cab heat....thought the thermostat would prevent that....Guess next time I go on leave back to Billings I will "invest" in some cardboard....LOL

 

Sounds like your thermostat might be stuck partially open, or should I say, can't close all the way. I'd check that. Mine does cool some on long downhill stretches of highway, because, as said, no fuel, no heat. But cooling enough to loose the heater in a short grade is a bit more than I'd expect. Still, running in -10 weather means some serious cooling from the wind blast.

 

I've never had any problems in the cold, and I am up in North Central Montana, once my engine is warm, then the cab is warm. That's running through the mountains in the winter time.

Idling around town is another matter, takes a long time.