Hmmwv overheating 220-240

[Bigfan]

Just picked up Humvee and drove today. Temps were hovering in 220s then jumped to 240. Outside temp 75. Cut it off and let it cool down. Drives like a champ other that heating up. No leaks.

Read through couple threads on here. Unplugged the delay mechanism To
force fan to run, didn’t drive after doing this. Figured this would help til I get it fixed.

My question being.....should I change thermostat first?, what are the possible
prroblems and solutions. Need to get this resolved as I want to take it off road but don’t want to hurt anything? Has 6.5L in it. Was carc 2006. All the fluids have been drained and replaced
prior to driving including radiator fluid. Only drove to mechanic to get fluids changed. Changed belts.

Thanks for help

 

[LouWon]

The thermostat is a good start, also check the radiator cap, if in doubt also replace it.
You mention that the fluids had been replaced, is the anti-freeze full??, is there an air lock.
The fan should be turning with the engine running, try unplugging the electric delay and look to see if the fan is engaging, it will also sound differently.

 

[ken]

The gauges in these trucks are known to not be accurate. Check the thermostat housing with a laser heat gun and go from there.

 

[papakb]

Normal cycling of the cooling system allows it to run up to 230 degrees and then turns the fan on until it cools down to around 180 degrees. The 16# radiator cap allows it to operate above 212 degrees without boiling and as Ken stated, with the inaccuracy of the military gauges your 240 figure isn't surprising. Now if it starts boiling or spitting water out of the reservoir I would go through the checks for the Kysor Cadillac valve and time delay relay. Their pretty well documented online and definitely in the -20 series manual flow chart/ troubleshooting charts.

 

[Bigfan]

I unplugged tdm, fan engages. Question will it hurt anything to drive it wilth the tdm unplugged short term? The end of tdm(gold canister) the end housing fitting appears to be leaking slightly. Seems there isn’t Teflon on the threads. Is this coolant leaking? Assuming that small of a leak wouldn’t harm anything til I can remove and fix.

Think i I will change thermostat with a new one just to make sure. I felt the hoses yesterday and they seemed hotter that my duramax in my truck.

is there a gauge I can replace with that is accurate. Seeing high temps even if it turns out being wrong worries me.

 

[LouWon]

If the fan is on all the time your fuel consumption will go up and you will loose some horsepower
Check the time delay, if the insulation on the wires is failing, you should replace it.
Make certain when you replace the thermostat that you get all of the air out.
Also check the coolant surge tank, remove the small coolant lines to check if the nipple is blocked, that is also a common problem

 

[911joeblow]

As mentioned, the big culprits are the thermostat, Cadillac valve, and dirty coolant. Whenever to change the coolant a thorough flushing is very important as field top offs were often with very dirty water. Also with trucks that were forded, the radiators get very clogged up and spraying water backwards up from the engine side can clear a lot of that out. Lastly running a cooling system upgrade kit really helps a lot of this as the stagnant rear coolant jacket area can cause a lot of temperature spikes and poor running. You can see the kit here:

https://paradoxbydesign.com/products/hmmwv-humvee-cooling-upgrade-system-v2

Here is a write up on the tech behind the kits:

https://paradoxbydesign.com/blogs/news/the-humvee-diesel-engine-cooling-paradox

 

[papakb]

Bigfan, the time delay module is the small rectangular box with the wires coming out of it and the Kysor Cadillac solenoid valve is the thing with the gold end. When the valve is disengaged by either unplugging the solenoid or the TDM it causes the fan clutch to engage. This is the fail safe mode of operation and other than being loud while driving and sucking up about 10 of the 150 HP your engine is putting out it won't hurt you to drive that way. When I first got my truck I had all kinds of problems with this and installed a switch to either let the fan run in auot mode, always on, or always off. That's the switch in the picture below. I would use a thread sealant rather than teflon tape on the fittings because you don't want to get tape anywhere in the hydraulic lines.

 

[Bigfan]

Drove some today. With the Tcm unhooked fan running constant, the temps never got over 200, per gauge. Not sure exactly what this means. Going to swap thermostat, temp sensor, and reconnect and see what happens. Have a feeling the TCm might be bad? Does kascar sell those as well?

 

[LouWon]

That good, yes for the temp sensor and the module.
I'm repeating myself here, but check everything, the nipples on the coolant reservoir often block, they are part of maintenance, as well as the radiator cap
Many small things to check, but when you add them all up, you have issues, they might look good, but...
Better spend a few hours covering all coolant components than breaking down on the road
Many suppliers sell them, some in the classified, about $80 to $100 depending on who you buy it from

 

[papakb]

The function of the time delay module is to give you a 20 second of free fan blade rotation during fording operations. If you quickly floor the accelerator pedal the linkage hits a switch on the injector pump that triggers the TDM to allow the fan to rotate freely. That way when the blades strike water they stop spinning rather than shearing off. That's it's only purpose and it does this by momentarily energizing the solenoid valve.

The thermostats are usually 195 degree thermostats so the 200 degree indication with the fan disconnected probably means that it's working fine holding the temperature in it's control range.

 

[Bigfan]

So I probably need a new tcm is what your saying?

The function of the time delay module is to give you a 20 second of free fan blade rotation during fording operations. If you quickly floor the accelerator pedal the linkage hits a switch on the injector pump that triggers the TDM to allow the fan to rotate freely. That way when the blades strike water they stop spinning rather than shearing off. That's it's only purpose and it does this by momentarily energizing the solenoid valve.

The thermostats are usually 195 degree thermostats so the 200 degree indication with the fan disconnected probably means that it's working fine holding the temperature in it's control range.

 

[cwajciec]

I think the temperature sensor is designed to make the fan come on at 230F and off at 190F. It does this by breaking Power to the TDM which opens a ground on the solenoid valve through a relay. It could be that your system is working as designed, and your temperature gauge is slightly off. Is it overheating and shooting coolant out of the overflow?

 

[2wheels70]

Make sure your guage is accurate
Mine will be in the normal to cool range then a few moments later will be way over to the 240 area
Tap on the gauge a couple times and watch it fall back to the normal area immediately

 

[Bigfan]

Thank you everyone. Everyone is so helpful. Good ideas. Told my wife not sure I would know what to do without this forum.

Bought a new gauge and temp sensor and thermostat. With fan engaged all the time Going to swap those (cheap fixes for peace of mind) and see what happens. Want to get everything working so when I go off road I don’t have an unforeseen issues.

Ordering a laser temp gauge to keep in truck.

 

[Bigfan]

Thank you everyone. Everyone is so helpful. Good ideas. Told my wife not sure I would know what to do without this forum.

Bought a new gauge and temp sensor and thermostat. With fan engaged all the time Going to swap those (cheap fixes for peace of mind) and see what happens. Want to get everything working so when I go off road I don’t have an unforeseen issues.

Ordering a laser temp gauge to keep in truck.

 

[Glenbob]

I purchased an 86 6.2 and it did the same but the thermostat had failed,it came apart(rubber separated and lodged in opening) ,installed new and it still heats up,not even fluctuating as it passed 180.I expected to see the point when it opened,but no change as it keeps on climbing.Any help appreciated?

 

[Dock Rocker]

I purchased an 86 6.2 and it did the same but the thermostat had failed,it came apart(rubber separated and lodged in opening) ,installed new and it still heats up,not even fluctuating as it passed 180.I expected to see the point when it opened,but no change as it keeps on climbing.Any help appreciated?

How are you verifying the temp? As you can see in the thread the factory temp gage is notoriously inaccurate.

Does your fan kick on at all? If so what temp is it showing when it kicks on?


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[Glenbob]

Found to be the problem,inaccurate gauge

 

[Dock Rocker]

Found to be the problem,inaccurate gauge

Never trust a military gage. Ever!


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