HEMTT Overheating While Driving

[bsteinborn]

I've got a 1986 HEMTT. The temp is stable at 180 degrees unless I start driving. It jumps up to 240 degrees not long after moving and I hear a large rush of air from the center console. Within a few minutes after I put the vehicle in neutral the temp quickly comes back down to 180 degrees. The problem doesn't seem to be either a thermostat issue or water pump since the temp stabilizes at 180 degrees. Wouldn't the temp stay high if the thermostats were stuck closed or the water pump wasn't working? Anyone know if detroit diesels run hot? My 5 tons with Cummins take forever to heat up to 180 degrees, the DD warms up fast. But it is a big motor. Thanks.

Bryan Steinborn

 

[Coffey1]

I sent you a pm

 

[NDT]

I recall a thread where someone had a plugged radiator.

 

[Coffey1]

The fan should engage at 190 disengage at 170
And that crappie Gage isn't worth a dime.
I changed mine to a digital

 

[Coffey1]

Try your best not to overheat it too many times it will kill that Detroit.

 

[snowtrac nome]

Try your best not to overheat it too many times it will kill that Detroit.

well said get it hot and the blower drive shaft will snap also always check coolant level a road oiler that gets run with out coolant on the heads will crack the heads the fire deck surface is pretty thin

 

[Gunzy]

If you can get or have a thermal reader use it to check temps at different areas of the block.

 

[73m819]

Get the 8v92 HOT, you WILL LOSE some heads.

 

[Elideclan2]

The gage is not accurate at all. Get a laser thermometer
And confirm the readings

 

[bsteinborn]

What temperature should the HEMTT be running at, 190? or 200? I replaced the sender unit. Verified the sender unit using a multi-meter. It seems to run around 190-200 degrees. Water pump is working fine. Replaced the sender unit with a barbed end and a rubber hose, green coolant comes pouring out at temperature. Figured it would run a bit cooler at 180 degrees. Used a laser thermometer too, reads around 190. At least it isn't running at 240 degrees!! Thanks for all of your inputs.

Bryan Steinborn

 

[Coffey1]

190 High 170 low

 

[JDToumanian]

The manual shows, and my truck has, 180 degree thermostats (there is one for each head), and a 195 degree shutterstat to turn on the fan. My fan seemed to rarely come on, yet the gauge read high, so I tested the fan clutch and replaced the shutterstat... It made no difference. But at least now I know that when the shutterstat does engage the fan, the temp coming out of the heads is right at 195, and the fan only comes on when I'm pulling a grade, so no overheating. The gauge is definitely junk, I can't imagine why they chose to use a gauge with such a useless range, the operating temperature of the engine being close to maxing out on the right side. I'd like to find a more appropriate gauge and sender that matches the appearance of the original.

You'll definitely want to verify everything, for as already mentioned, you don't want to overheat the engine. There are a lot of critical o-rings in a Detroit, and overheating will cause them to fail, resulting in coolant in the oil and accompanying destruction of the bearings.

Jon