Humvee Overheating

Could be, but I figured the fan should have came on at least once on the way home.

Keep in mind these guages aren't the most accurate. My truck for 14 years will kick the fan on at 240 (which imo isnt really super hot for whats going on inside the engine) then the fan kicks in and you hear it kick in and the temp always drops. If any one part of the cooling system is bad the system will always run in the safe mode and you will run very cool. Diesel's work better hot vs too cool.

Yeah I know, I've just never seen it get much above the 200 mark before and I really don't want to have to deal with a blown head gasket haha. I drove it a little today to see what it did and the fan came on when the gauge read a little under 200 and everything was fine. I'm still thinking the thermostatic switch is sticking a little and I already ordered a new one since its probably as old as the truck is.

Your fan is operating normally. Pressure from the power steering pump disengages the fan, but there is still some parasitic drag so it spins slowly. You should be able to stop the fan from spinning rather easily when its disengaged. With the truck off there is no pressure so the fan is engaged and it should not be able to spin independent of the pulley its bolted to.

1993 said:

Before it kicks on is it normal for the fan to spin at all?
I just picked my Humvee up a few days ago and only ran it long enough to inflate the tires and drive up onto the trailer.
started right up on a 20ºF day, batteries look new.
air filter was last "blown out" in 2012 and still looks very clean.(probably hasn't been used much since 2012)

turned it off as the gauge crept towards 220ºF(made me nervous, i'm used to temps staying at center of range)
didn't hear it kick on. but it did spin at a relaxed speed from the moment the engine was started.
It is in fact immovable when engine is off.

I've never seen belts as loose as these.
After getting home(3hour drive) I noticed a coolant spot on my trailer deck. found a loose clamp on a hose connecting top of radiator.

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First time your fan really kicks on, you will probably pull over thinking something bad happened lol, it's loud and you feel the engine power reduce. You will know when it kicks on.

Mike82ndABN said:

First time your fan really kicks on, you will probably pull over thinking something bad happened lol, it's loud and you feel the engine power reduce. You will know when it kicks on.

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I wish someone would have told me this before I got mine in the road the first time! I thought the truck was about to fly apart.

Replace my dead fan clutch switch and now the fan comes on when it needs too. Temp when it comes on is around 220 degrees. I know the temp gauge are not spot on but now I know its working after repair. Only gets hotter when driving then fan comes on. Just fyi for other owners.

I have a 1989 M998 and the temperature keeps going up to 230 and I shut it off cause I don't want to cause any damages when I unplug the time delay module The fan kicks on and cools the engine down to like 140 I'm just worried if it's over 230 it's going to burn the engine up could it be the time delay module?

If the fan comes on and cools the motor down to 140, I would try a different gauge.

Overheat

Action said:

If the fan comes on and cools the motor down to 140, I would try a different gauge.

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. It only cost down to 140 when I unplug the thermostat control module and the fan runs nonstop

FWIK:

A thermostat is supposed to prevent cold fluid from circulating in order to allow an engine to warm to operating temperature. Once the minimum operating temperature is achieved it should then activate a fluid relief valve that allows water to spill out towards the radiator in order to keep the engine at operating temperatures and not above. If you're overheating and if your valve is incorrect or oriented incorrectly, you should be able to remove the valve and see if the overheating issue disappears. That will clinch the diagnosis.

Best,

T

EDIT - I just noticed in an earlier post that RWH also mentioned pulling the thermostat to see if she overheats or not.

I have a thermal thermometer that I have checked the running temperature of the engine and the gauge is correct

I have never seen one of these run with a temp of 140. 185 - 195 is more realistic. That is why i suggested s different gauge.

I have a 91 6.2. I had the water pump go out. I had a pin hole in the crossover pipe (tube bent 1 each).so ended up replacing radiator, water pump, and pipe. Cooling system is working great. The old parts looked original, and seriously past normal life.

Need some help here....
2 years ago, fan wot working....replaced it all, solenoid , fan clutch switch and temp censer... worked fine.(till now).
fan was coming on fine, till a hair pin turn to my street, and the system blew the hose on the solenoid...
cleaned everything up.. refilled (got all the air out), and now fan wont come on? but it kicks on when turn steering to way hard right or hard left??
any input ????

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Totally agree with Retiredwarhourses - first thing is to confirm the temp gauge: go by a cheap laser temp, and confirm the engine temp by pointing it at the top of the radiator, or the thermostat housing.

If you are running hot, and the fan is not on, then you can disconnect the upper temp sensor (right behind the thermostat housing; it has two wires coming out of it). Disconnecting the upper temp sensor will cause the fan to come on and stay on. (I tested this, and my hummer runs at about 165 in 90-degree weather with the fan on non stop). If your fan does not come on, then there are other issues that some of these other threads mention.

A while back, I had a leaking heater hose, all my coolant leaked out, and my hummer overheated. I shut it down (obviously), found the loose clamp, tightened it up, and refilled the coolant once it cooled down. However, on the drive home, the hummer consistently ran at about 235 (versus normally 200-210). I checked the thermostat housing with a laser thermo, and the temp gauge was reading about 20 degrees high. I replaced the upper temp sensor, because I noticed one of the two leads was frayed - no change, the temp gauge still read 20 degrees high. I figured that maybe maxing out the temp gauge when it overheated might have broken it, so I replaced it with a new one. Now, the new gauge read 20 degree low (I'm not making this up). I then found out there is a second temp sensor, in the block (on the driver's side, near the front of the engine, just above the exhaust manifold). After replacing the second gauge, now the new temp gauge is accurate.

There are three electrical temp sensor. Each one is for a specific use. Not connected / independent to any other electrically.

Cold start advance to IP = right side rear engine > switch.
Fan control - Time delay module - Solenoid control = Water crossover > switch.
Temp gauge = Left front side of engine > Temperature sensitive resistive element.

Simple circuits, simple truck, CAMO