Humvee Overheating

1993 Humvee with 17k. Replaced thermostat suspecting old one was stuck. New NAPA one I believe it's a 190. Seemed fine for last couple days driving around about 40 mph weathers been in the 50's. Same weather today driving on the beach slower speeds, humvee gauge reads 240. Is this normal for these? Don't smell coolant or see any overflow. Seems to run warmer than cooler in general. Worried what it's gunna happen when it's 90 degrees outside.

I've never seem mine get over 200 with a new thermostat and water pump. In fact it usually sits around 170 unless I get on the highway and then it creeps up to sit just below 200. Is your fan coming on?

Isn't the 6.2 a belt driven fan off the motor?

yes, but it has a clutch that is actuated by pressure from the power steering pump that goes through a solenoid and turns it on and off.

My 6.2 runs about 200, I just flushed out the cooling system, it needed it, it only has 13,000 miles on it.
There is something that controls the fan near the washer fluid tank, its a little black box
I just changed all the fluids and filters on my Hmmwv

Driving around it stays at about 200. It shouldn't be running 240 in this weather not being abused. It seems like every time I open the hood the fan is spinning. I'll do a coolant flush just to be sure fluids are good. Old t stat was a little crunchy. I'm considering running a top aux fan since this will see a lot of beach time and slower speeds. I just figured these things see hot weather and standerd cooling would do. Should fan not spin at all until 210 or what ever the switch temp is?

I would think fan should not spin until solenoid actives it but not sure what that temp would be. My solenoid is brand new I can check it for a part number and maybe it will say what temp its set for

If you unplug the Cadillac valve on the left side while running you hear a difference in the fan pulling air.
Also with the engine off you should not be able to spin the fan unlike a normal viscous clutch.

ill check the fan tomorrow and see if it kicks in when it's supposed to and functioning. I'll post tomorrow when I got some more info. Thanks

All nine of mine get to 220-230 before the fan really kicks on. Normal operating temp.

Nine! Nice! I've read from a few places that temps in the 230's isn't bad. What are your temps like in summer months just cruising around? Do you ever have any over heating issues? Mine hit 240 so I question what the fans doing.

Driving home tonight. Temps where in the 200-220 range. But any long periods of idling or moving slow and temps creep up.

Relay, cooling fan, time delay. NSN: 5945-01-193-7175, PN:L 12338603.
http://www.easternsurplus.net/HMMWV.html

take it in and have a mech check it out thats to hot.

over heating while driving home off road only??? hummm......... might be the fan clutch or plugged radiator do you have cold spots on your radiator?

Your fan will not turn on until the temp reaches 220 degrees, then it should decrease or at least not rise about 220 too much. I would do a flush and replace the thermostat. Also, the sending units for the fan clutch and gauge are separate, and the actual gauge is not usually very accurate.

Ok folks...lots of misinformation going around.
the cooling system on the hmmwv is simple, yet over engineered, like all things military these days.

the HMMWV uses a hyd fan clutch, assuming everything is working the fan free wheels when cold, it is NOT locked, so it's not moving air, you will know when it comes on...trust me.
your thermostats are set to open at 180-190, if you are using mil spec stats. The fan should not engage till 210-215. The way it works is that you have a time delay module and a Cadillac vaave solenoid, there is also a temp unit in the water crossover on the left side, wire 458 IIRC. When the temp get to 215, that sender closes, supplying 24v to Cadillac valve solenoid, thus stopping fluid from flowing to the fan clutch, this in turn engages it, now the TDM or time delay module takes over, it leaves the fan on for say 1min, then turns off and the fan disengages, this repeats itself every " I can't remember". The override to an engaged fan clutch for purposes of passing and fording are to mash the accel pedal to the floor, this causes the switch on the right side of the Injector pump to kill the 24v to the Cadillac valve, as you know, you loose quite a bit of horsepower when that fan is engaged.

remember, that a bad TDM, Cadillac valve or thermostatic switch will default the hyd fan clutch to engaged, the easiest way to test is unplug and plug back in the TDM connector with the 2 wires on it, as you do so, watch for the fan to move in and out from engage to disengage or vice versa.
Now, I also see a lot of stuck on fans due to the clutching plates in the fans stuck....this requires you take the clutch out and beat it with a mallet...you can use 90psi air into the fan clutch to simulate the hyd fluid function.

do NOT trust you temp gauges....they lie badly, you can buy cheap laser thermometers to get the true temps, Ot put a thermometer in the cool and tank.

a clogged radiator will cause running hot issues, so take it out, send it out and have it rodded, unless it's new and you know it's new.

water pumps either work or they dont, and you will know in a few minutes if it does not work.

Oh...and the number one reason for hot running truck I find is a bad radiator cap.
in order for the cooling system to work correclty, glycol requires it be pressureized to raise the boiling point, if the cap is let out pressure, the coolant cannot do its job, the cap is 15psi.
the other issue is the overflows inlets back to the coolant bottle, these have to be clear or you will run hot.

TucsonVTXF said:

over heating while driving home off road only??? hummm......... might be the fan clutch or plugged radiator do you have cold spots on your radiator?

Click to expand...

I don't see anywhere in the OP's original post that he was driving off road, nor do I see anywhere that he states this truck was recently bought from a government auction. Could be a legally titled HMMWV. Why don't we just stick to the OP's problem and not speculate about weather or not he is operating legally or illegally.

To clearify we own a private beach house on private roads. The Humvee lives out there. I unplugged the time delay module tonight and the fan kicked in. After hearing the fan I can't say that I've heard this come on while driving. Would a bad time delay module cause the fan to not engage and the truck run hot? This fan pushes some air I couldnt imagine this truck overheating like it does if the fan functioned right.