Humvee Overheating

[jeremymx26]

Could be a delay module. Also could be a fan cut out switch, fan temperature switch, etc.

There is some great diagnostics and multimeter measurements in
TM 9-2320-280-20-1 page 2-168

 

[Retiredwarhorses]

Yes..TDM is the highest failure rate item in that system, then the Cadillac valve solenoid.

 

[Woodshumvee]

Going to order a TDM. It's been staying at around 219 will driving. I still can't hear or tell if the fan is ever coming on to keep it there or if the radiator is just doing its job and it's not getting hot enough for the fan

 

[Woodshumvee]

Update. Ran up over 240. Pulled over while running fan was not on. Unplugged TDM and fan turned on. Limped home but temps never really came down. Ended up boiling off quite a bit of anti freeze. Got home cooled down and topped fluid back off (3 gallons) Had out today with fan unplugged and temps went up over 240 after about 15 mins. Over flow cap bubbled when cracked. Lost a little fluid. Do any of you guys pull the thermostats in the summer??? I don't know why it would overheat so fast with fan on 24/7.

 

[Retiredwarhorses]

Did you replace the thermostat? Did you replace the coolant bottle cap? Is your fan installed correctly? Meaning the blades are moving air in the correct direction, they can be installed backwards.
Lastly, you very well have a blockage in the coolant system. I would remove the radiator and have it cleaned and tested.
also, very important...make sure the overflow line from the radiator to the coolant tank is clear, as well as the nipples into that tank, also check or replace the line from the water crossover to the coolant tank.
all of the above will cause your issues...especially the drain back lines into the coolant tank.

 

[Woodshumvee]

T stat is new. Cap holds pressure and dosnt leak when hot but I will replace. I'm going to get into it and overhaul the coolant system. Are cracked cylinders or head gaskets a huge issue on these 6.2 vs the 6.5 issues? I'm not seeing or smelling burnt coolant so hopefully it's not damaged. Fan is indeed sucking air through the radiator and over the motor. I'll clean and replace hoses as needed

 

[ZZ4x4]

A couple minor points to add. The fan switch on the coolant passage can fail in either the open or shorted position. This means the failure will cause EITHER the fan to stay engaged, or stay disengaged. Mine failed keeping the fan disengaged. Also, it's important to note the fan will always spin even if disengaged. It is freewheeling but is spinning fast. If you are not hearing the loud roar from the fan, it is probably not really engaged. Old fan friction linings can slip. They can be replaced without removing the fan or hub ( unless you have the AC with 5 groove pulley). If you do have the AC pulley, you need to loosen the hub and pull it out a few mm to get the linings out.

 

[Retiredwarhorses]

The drain back lines to R&R is a 15min job....as well, check the inlet on the bottle, I drill them out one over, this way they are clean and open.
i had a customer truck that had this issue....both those lines and overflow tank were clogged with rust, casting sand and a clump of RTV. The lines were impacted for more then half the lenght of the line, I fileted them open and was amazed.
the culprit for the most part turned out to be the heater core, while flushed had been done, the heater core needed a full flushing of its own, simple enough....bout man, you shoulda seen what came out of that thing.
once done...all was perfect, she runs under 200 now.

 

[Woodshumvee]

ZZ4x4. I deffenetly have a failed something since I am overheating and fan does not turn on ever. When I unplug the TDM with the truck overheating the fan slides 1/4 forward and roars. Plugging the TDM back in when it's still hot disengages the fan. I just need to figure out why and where the fail is. I can feel a tremendous amount of heat being pulled through the radiator when it kicks on.

Now with the fan bypassed and on I'm still running hot. Not sure if once it get to hot it's hard for the fan to catch up. Temperature does not come down. I'll over heat all the way home, fan on, and driving.

 

[Woodshumvee]

Thehummerguy it's funny how temperamental these are for such a built machine. I'm a few posts away from starting a 4bt build thread.

 

[Retiredwarhorses]

Thehummerguy it's funny how temperamental these are for such a built machine. I'm a few posts away from starting a 4bt build thread.

yes, at least this piece of it...this part of the system either works or it don't, as pointed out, your system has failed in the disengaged mode, I had that on a truck, it was the TDM, but the water crossover temp switch can be bad as was pointed out, that's a simple one to test. Just unplug both connections and test leads 458, IIRC they are normally open, don't quote me....once engine get to 200ish the switch will close, sending 24v to the TDM and Cadillac valve solenoid.
So, either test for 24v while it's all connected, or just test the switch while it unplugged....you should have 24v on one leg of wire 458 with truck running, the 2nd leg should be dead.

 

[63foxtrot]

upgrade to a 6.5L, recore your radiator.

 

[ZZ4x4]

Hey Woodshumvee, I think we can eliminate a few potential issues: The fan control solenoid is working fine and you are getting more than 90 PSI from the PS pump to the fan clutch since you can see it move in and out. Fan clutch linings are probably ok too since you hear the roar. It also appears the coolant is REALLY getting hot ( not a gauge issue) since it boils over.

It sounds to me like two problems.
1) Fan switch or Time delay module issue ( but this is not causing the overheating since you've unplugged the TDM). It is easy to check the fan switch if you remove it and put it into boiling water ( carefully ) with an ohmmeter attached. The switch should open and close around 215 degrees. The TM has a nice trouble shooting guide for the electrical checks including the switch and TDM. Do you have the TM?

2) There is a restriction in the coolant system. You mentioned it gets higher than 240 F after 15 minutes and it boiled over 3 gallons on one of your trips. Just to compare , my HMMWV has a new radiator , hoses, t-stat so I know it's not restricted. When my switch failed I noted a max of ~230 in Texas (with no fan operating) and it would take ~20-30 minutes and no boil-over. In colder air ( less than 60) it never overheated even with no fan operating. After being fixed the fan turns on at 215 and it cools back to 200-210 in just a couple minutes.

Are you sure your t-stat is the correct one and installed the right way in? I purchased a civi Hummer T-stat and noticed the length and style were wrong. If I had installed it the center pin may not have been able to move since the HMMWV cross-over is apparently not as deep. I also can verify what Hummerguy says about these trucks needing a flush. You might try pulling the lower radiator hose and see what you have there. Possibly sand and sediment ....

 

[Woodshumvee]

I did notice my new t stat was slightly longer ZZ4x4 like maybe a civi version. (Bought from Napa) Ordering a Humvee one now. What is proper orientation? I put mine in the way I took it out but may have been wrong all along.

I will get my fan switch off and test in water like mentioned. And do a good flush and rad inspection.

You guys have been a huge help through this and extremely informative. Hopefully I can resolve and help others with similar issues.

 

[Retiredwarhorses]

You need to read the TM's, it covers this issue and has TS procedure.

 

[ZZ4x4]

I did notice my new t stat was slightly longer ZZ4x4 like maybe a civi version. (Bought from Napa) Ordering a Humvee one now. What is proper orientation? I put mine in the way I took it out but may have been wrong all along.

I will get my fan switch off and test in water like mentioned. And do a good flush and rad inspection.

You guys have been a huge help through this and extremely informative. Hopefully I can resolve and help others with similar issues.

The longer end should go into the crossover pipe. I suspect if you managed to get the civi t-stat installed then it is in backwards. At at least on my HMMWV, there is no way the civi one I bought was going to fit (unless compressed by the mounting bolts). the correct t-stat should have plenty of room inside the crossover .

 

[hummer4x4guy]

If any part on the fan system is bad the fan is suppose to fail safe and turn on all the time. Odd situation tho. I dont have any other good advise to add.

 

[saddamsnightmare]

May 13th, 2015.


Amazing how an engineer with a computer can design a cooling system so fouled up it takes a true genius to fix it! At one time cooling systems were: 1. a radiator; 2. a thermostat (or not, depending on if it was a thermic syphon system); 3. a water pump (or not, see # 2 above), and 4. possibly a thermostat or two. You have to ask yourself how they managed to get a combat truck system so complex that it takes a master mechanic to repair it. Used to be farm boys could do it just about uninstructed.

This is probably why so much of our equipment today is unreliable under combat operations and maintenance....It's TOO complex..... Good luck and happy hunting!

 

[DatGuyC]

Alright, now I've gotten hit by the overheating hmmwv bug. Let me first say that pretty much everything in the cooling system is new except for the radiator. Its never really given me a problem and usually stayed right below 200 with the fan operating normally. While I was running it around this morning I noticed it was suddenly right under 240 after idling for a couple minutes. I shut it down and let it sit to cool off a little before I limped it the couple minutes it took to get back to the house. The fan never came on and the temp gauge was at about 220 the whole way. I remembered this thread and decided to do some testing. When I disconnected the switch in the coolant crossover the fan came on almost immediately and when I reconnected the switch the fan turned off. I did this a couple times with the same thing happening every time. I'm thinking that the crossover temp switch is normally closed and when it gets hot it opens and this signals the TDM to turn the fan on. Since the fan turned on and off with no problem I don't think the problem is the solenoid or the TDM, probably the thermostatic switch getting stuck closed. I'm hoping this is the problem since the switch is the cheapest part of the whole system haha

 

[trooper632]

Wonder if you have a faulty gauge?