Big overheating issues. Help required.

6.2L
No leaks at all, good engine pressure. Fan stopped cutting on this past winter. Now if idling more than 5 minutes she shoots up to 250 and overflows.(have since stopped driving.)

Being in the middle of an expensive move I do not have the money for process of elimination. Anyone have a good guess as to whats going on and a solution? I know I'm asking you to do operation on a patient behind a curtain, ask any questions and I'll answer them to help you help me! Someone earlier mentioned before I could unplug a sensor that would make the fan run 24/7? Does anyone have a picture of this sensor/wire?

Many thanks

Sounds like your fan system is not right. Easiest check is the temp sensor wires, per TM, the sensor that is near the thermostat. Then check the Cadillac valve, also called the valve solenoid (some are marked Cadillac manufacture, hence the nickname). You might also check your fan is not always clutched in (but overheating it is almost certainly not). Can check fan clutch by carefully putting 2x4 into the fan when running at idle, it should stop because it's only free wheeling. Pay attention to the direction of the fan blades and approach them with care. Since the fan clutch fails closed, for over cooling, it's probably not your problem.

The fan clutch gets its pressure from the steering pump. How is your steering? Is the reservoir full? Is it ATF/Dexron in the steering system? Some people unknowingly put power steering fluid in the steering box. The HMMWV system is designed to use Automatic Transmission Fluid. After checking all this you might try bleeding the steering system of air, it's also in the TM. If your wiring is good (check with multimeter for continuity where you can) it's likely the Cadillac valve.

As far as being on a budget, I can say from personal experience it is possible to carefully tear apart and put back together a Cadillac valve. Since doing that mine functions file. I wasn't able to take many pictures, but it's not a complex piece of gear, just move slow through it and use your eyes.

While you're in there it's not a bad idea to replace all the high pressure steering hoses on the Cadillac valve. Not expensive really. BE SURE TO GET PRESSURE HOSE, not oil/fuel hose. It's marked for power steering applications. Your auto parts store should know the difference. It's thicker walled is all. Use the best hose clamps you can get (Uncle Sam doesn't) so the pressure is well-contained.

Give us some more feedback and we'll do our best to advise.

Bulldogger

Sounds like the same issue as this thread ;
[h=1]6.2 running at 240 consistently.[/h]

Take out the thermostat, top off antifeeze (or water if you going to flush the system anyway) and see if issue goes away.


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Near the washer fluid bottle (in front of driver) is a hand sized black box with wires coming out both sides. Unplugging one end should make the fan run constant.

Thanks for all the help, I should be able to unplug that now and get the fan going to cool er down until I can find the true culprit.

5 minutes Of idling and it over heats is a bad thermostat, not a non-working fan clutch system, not that the fan clutch system does not need to be fixed before you go driving. Folks need to understand how cooling systems work, this is not specific to the hmmwv.
Even a faulty coolant reservoir cap can cause overheating.....

Retiredwarhorses said:

5 minutes Of idling and it over heats is a bad thermostat, not a non-working fan clutch system, not that the fan clutch system does not need to be fixed before you go driving. Folks need to understand how cooling systems work, this is not specific to the hmmwv.
Even a faulty coolant reservoir cap can cause overheating.....

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I was thinking the same thing. Thermostat needs to be replaced. Ensure that you by the Hummve specific high flow one. Also nothing wrong with disconnecting the TDM as part of trouble shooting. If fan turns on then TDM or Thermostatic fan switch are bad. otherwise it's the Thermostat

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WHAT! 2x4 into fan to check for WHAT!!! Did I read that right? And what IF it is engaged, lock up, rusted, busted ? USE a 4x4 for a better effect of shards of plastic fan parts and wood splinters.

There's a lot of good info here. This isn't one of them... especially for many that are new to, or their first go at the mechanical going on's with this rig.

Moving part and sudden stops DON"T MIX.

At least wear your safety glasses.

With all due respect sir... I disagree with the General.

CAM

I used my fingers slowly. If you enter a fan from the downwind side, the blades should push whatever back out. As long as you dont hit the leading edge of the blade. Just speaking scientifically. I do not suggest doing it.

I wouldnt recommend that either unless you dont need your fingers. I get the concept all you really need to do is apply some resistance to the fan. If fan cluch is not engaged it will slow down. Don't use your fingers or 2 by 4. Just some thing that will provide resistance.

Action said:

I used my fingers slowly. If you enter a fan from the downwind side, the blades should push whatever back out. As long as you dont hit the leading edge of the blade. Just speaking scientifically. I do not suggest doing it.

Click to expand...

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I'm looking up thermostats and it seems most everything now is for H1s, so I'm a bit confused on what exactly I need?

Anyone have a part number or better yet a link to a place with them in stock for not a benduover price?

I do not believe it's the radiator cap but I may go ahead and replace that too just to be sure.(only $10 so not a big deal)

Kascar or the hummer guy.

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Thanks much, had no idea about Kascar.
Got my stuff on order!

suzukovich said:

Kascar or the hummer guy.

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5 Min of idiling? Mine doesen't make it to 160 when idiling 5 min. I wonder if you have a head gasket leaking exhaust gas in to the coolant. Are you getting any bubbles in the over flow tank?

ken said:

5 Min of idiling? Mine doesen't make it to 160 when idiling 5 min. I wonder if you have a head gasket leaking exhaust gas in to the coolant. Are you getting any bubbles in the over flow tank?

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5 min of idling, I am just getting to 120 and that's on a hot day. If he is getting to 240 or more in 5 minutes Its more then a cooling issue. That sounds like the water pump is shot, the radiator or something is impeding the flow of coolant as there isn't any circulation. But still the fan should kik in.

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Coming in late to the party, but I doubt the thermostat would cause that fast of an overheat. In fact I have a hard time believing it can get to 240 in 5 mins period. So how do we know it is really 240 and not an infamous bad gauge? I would run a set of jumper cables from the block to the negative terminal of the battery before it goes to the chassis and see if the gauge reads differently. Even a bad pump, frozen thermostat and no fan will take some time to heat to 240.

Now if somehow this is heating that fast then a few things you can do quickly. Pull the thermostat cover and start the truck cold. Does coolant shoot out? If it does your water pump is good. While the thermostat is out, throw it into a pan with water in it and turn on the heat. Watch it and see if it opens as the water reaches boil. If it does, that is good to go. At this point I would start worrying about a head gasket or cracked block/head(s). Pull your dipstick and check for milky oil. If it is whitish or light brown, well bad news. Are you losing coolant out of the overflow? If you are then either your pressure cap is bad or you are pressurizing your cooling system with combustion pressures. If still no smoking guns then you will need either a chemical tester to sniff the coolant for combustion gasses or a really good leakdown tester and high pressure air/gas to pump into the cylinders (100psi may not do it as combustion pressures are MUCH higher) and watch for air entering the cooling system.

Good luck!

Thanks for all the wonderful info all.

I just got in the parts for kascar(30 minutes down the road from me!) with both a new thermostat and a new gasket for it. The oil looks good as does the pressure, so I believe it's some sort of a flow issue, either with the water pump or maybe the radiator but I am getting NO leaks at all of anything on the vehicle. I'm hoping it's not anything cracked. Keeping fingers crossed!

I'm assuming the thermostat is just plug n play? Will find out shortly.

Pump worked fine, coolant rushed out. The original thermostat looked to be in decent shape but the gasket had completely disintegrated. Replaced them both to be sure.
Temps still climbed up to 220f(and I'm assuming 240f if I had not just shut her down.)

Unplugged the TDR and sure enough she was running last night at 190f for a good hour of driving. I'm guessing during the hot summer days another 10-15f will be added to that but even at 200f it'll be the lowest temps I've ever had with this vehicle.

Next culprit will be the radiator cap, I doubt that's it but crossing my fingers. After that I'll look at replacing the radiator which is NOT leaking but looks fairly old and beaten up. Not seeing anything but pure black oil from the engine so I am assuming there's not a cracked block or blown gasket, could still be the issue but I'm leaning towards that not being an issue.


Will update the thread when I find out what the issue is. Sorry for the double bump but wanted to update.

Again thanks for all the help.

Just a thought on the head gasket. If you have a leak that is allowing exhaust gasses into the coolant, you wont have any water in the oil or oil in the water. I'm not saying this is your issue. But getting that hot in 5 min ins't right. While the thermostat is closed the coolant will flow through the bypass hose. Keeping coolant in the engine. So it still should take longer than 5 min to get that hot. Are there any bubbles coming into the overflow tank? Glad to hear it didn't overheat after a hour of driving.