ok...i have used search and have read pretty much everything on overheating.....a new to me (about 6 months now) 98 3500 QC dually 12valve....supposed to be stock other than upgraded transmission and striaght pipe exhaust....i tow all the time...horses/cattle/hay etc...when i first got the truck i could really put my foot into it on the hills...and there would be no overheating issues...all of a sudden while towing up the coquihalla connector with about 12,000 lbs of hay on a flatdeck....there was a kind of surge for just a second...and then a few minutes later...the coolant temp started to climb...this happened in early spring...

after that trip...i could easily get the coolant very hot while towing...

without a load...the temp doesnt move at all..since then...i have put in a new thermostat (not cummins), radiator and replaced the stock tranny cooler with a 26,000lb rated flexalite...this has improved things substantially but i can still get the temp guage to go into the red if i really put my foot into it...i feel that something has changed since that spring night when the engine coughed...i never lost power (or so it seemed towing up a steep grade) and i know on my 97 12v...i can pretty much climb any hill with a trailer and not see much in the way of temp movement...

i dont think it could be head gasket as i am not losing coolant...i have checked temps with an infrared gun...in case the sensor was not working correctly...the transmission fluid stays substantially cooler than the coolant...(at least at the tranny cooler...dont know about that exchanger below the turbo)...

have not torn into the fuel plate or afc yet...was wondering about likely places to look to try fix what i dont know happened...lol...

could timing go out of adjustment during a drive?? that whole "hiccup" thing and then higher temps really bugs me....thx...vs

 

I would start with a cummins stat first, simple and fairly cheap part to try.

 

check thermostat, coolant pressure test and see if it leaks off, check water pump if all else checks out.

 

The fan clutch could cause overheating at low speeds in a strain and also a plugged radiator can cause the same thing. You may need to pull radiator and take to a shop that can remove tanks and "rod" out the cores. Make sure they rod and not just boil it out. Diesels have a bad habit of clogging the flues with some nasty stuff.

 

my 97 was doing about the same thing not even getting up to 190 unloaded. hooked a 20' gooseneck to it and it would get hot. then all of a sudden oil in the radiator. my oil cooler had a pin hole in it.

 

X2 on the fan clutch... I hit some mountains this weekend and it would creep up to 190 on the mountains and I could hear the fan over the twins and stack but it wouldnt go past 190 once the fan came on.

 

thx guys...as i said in the post...brand new rad and new tranny oil cooler...will switch to the cummins stat and put in a new fan clutch...can the water pumps become slowly ineffectual?? or do they just stop working???

have not done pre-filter or overflow valve since i bought the truck...could either of those contribute??? vs

 

Sorry about the radiator. I read right over it and it never sunk in you had already replaced it. I don't believe running lean would cause overheating. It will cause bad things in gas engines, but diesels really don't make much difference with a lean mixture across all cylinders. They get all the air they can pull in most of the time. Only time a lean situation would cause a problem would be if one cylinder is running lean like with a bad injector. Normally a water pump is bad due to bad bearings, seals or both. Unless the impeller comes loose on shaft, water pump should circulate water. If you have some horrible corrosion or rust then I guess impeller could not do the job, but that is unlikely. If you would like to look, pop off belt and three bolts and take a peep.

 

Get a new OEM fan clutch, not an aftermarket. The OEM clutch will engage much sooner than any aftermarket.