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Thread: HMMWV Overheat Q's and pictures

  1. #101
    Sergeant Major McSpeed's Avatar
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    AH...this makes sense. Per that posted manual, this explains why the fan kicks on and off. I usually notice this when I'm cruising at 55 or so. This summer I've been using the truck to take my boat to the lake. I'm on the throttle pretty steady to keep it pulling, which may have it in kick down mode. This is why it goes on and off:

    B. TIME DELAY MODULE TESTING
    a. Description
    The time delay module sends a delayed
    signal to the fan clutch solenoid for delay
    of fan actuation to provide needed
    horsepower for engine acceleration. During
    normal engine operation [(engine coolant
    temperature below 230F) (110C)],
    current flows through the time delay module
    energizing the fan solenoid circuit This
    provides hydraulic pressure to overcome
    spring pressure thereby disengaging the
    fan clutch.
    When engine coolant temperature exceeds
    230 F(110C), current is interrupted by the fan
    temperature switch. This interruption of current
    causes the time delay relay to open, thereby
    de-energizing the fan solenoid circuit and
    allowing the fan to engage for additional cooling.
    If the kickdown switch is actuated during fan
    operation, the time delay is activated,
    disengaging the fan for approximately 20
    seconds and providing additional
    horsepower. If the kickdown switch is
    activated again, an additional timer within
    the time delay module prevents the
    disengagement of the fan until 20 seconds
    has elapsed allowing for adequate engine
    cooling. After the timer completes its 20 second
    cycle, the kickdown switch can be reactivated
    and the fan will disengage, providing additional
    horsepower.

  2. #102
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    Ok, so they sent me one that looks and fits like the OEM one I had. The temp now rises to 220 before the fan clutch engages. It no longer cools down to 200 but cools to about 218. The fan re-engages at about 220 keeping the temp at 220 or below at all times. I also notice the fan only runs for short periods of time now since it is obviously not cooling the engine temp down as much. On my normal 20 mile trip to the farm the fan clutch engages a couple of times when it used to come on 3 or 4 times. Does all of this sound ok/normal to you? Should I have any concern about a continual engine temp of 220? My coolant is clean and the truck shows no signs of overheating. Thanks for your help.

  3. #103
    4 Star General Retiredwarhorses's Avatar
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    Quote Originally Posted by David172 View Post
    Ok, so they sent me one that looks and fits like the OEM one I had. The temp now rises to 220 before the fan clutch engages. It no longer cools down to 200 but cools to about 218. The fan re-engages at about 220 keeping the temp at 220 or below at all times. I also notice the fan only runs for short periods of time now since it is obviously not cooling the engine temp down as much. On my normal 20 mile trip to the farm the fan clutch engages a couple of times when it used to come on 3 or 4 times. Does all of this sound ok/normal to you? Should I have any concern about a continual engine temp of 220? My coolant is clean and the truck shows no signs of overheating. Thanks for your help.
    220 is the normal range....don’t trust the gauges to be exact, they aren’t.
    sounds like a normal running truck.
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  4. #104
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    Quote Originally Posted by Milcommoguy View Post
    I note your new to forum? Just got a Hummwv? These cooling issues can be learning experience to new owners and old ones too. ...
    As the 4 Star stated, unplug it and drive it. This is all you got and you have to get back to base or pick up supplies (beer) or dodge some bullets. It shouldn't ever get too hot. It should regulate on the mechanical thermostat and that too is a test. (may run a bit cooler) If it runs hot pushing the 240 mark, you have other problems, like clogged up anything, thermostat or a pump. (got water?)
    .....CAMO
    Yes I am new to the HMMWV. Six months ago I discovered GovPlanet and didn't own any HMMWVs.....Now I own two..... .
    I am grateful for everyone's advice, especially yours and Retiredwarhorses. I have already learned a lot from all of you guys on this and other threads.

    Duly noted about the multi-meter. I am going to dig mine out. As per the General I will disconnect my TDM until the new parts arrive. Do you know if any quality thermostat made for a GM 6.5L engine work in the HMMWV? Kascar lists several thermostats but I can't see the difference (except the one for the 6.2) unless they are different temp ratings.

    Your advice is most appreciated.

    https://real4wd.com/store/catalog/se...rds=thermostat

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  6. #105
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    Thanks so much for your help. I REALLY appreciate it.

  7. #106
    Colonel Milcommoguy's Avatar
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    Things to think about... IMO. COOLING SYSTEM

    Just won the rig? Study up on the TM's or manuals while waiting for the EUC. Good chance the dealer / sales person NOT going to do a walk around, a test drive or point you to the book in the glove box.

    Flush the system really good. Rig maybe new to you. Well, some parts might be almost new...Ah, not so much. Just got it in...a sweet "89" model?? from sitting for HOW many years.
    Use quality brand name parts. Going cheap could take out the whole engine.
    Buy from reputable suppliers. They have been there, sold that. If it doesn't make sense ASK questions.
    Stay with recommended temperature ranges for thermostat. Going to a 170 or 180 temp engine will not be happy and you'll thank me in the winter.
    You got the STAT out? Run it up in the driveway real quick, make a mess, checking pump flow. Shut it down
    Check and clean crud between radiator stack.
    Straighten fins works better. Slow and PITA.
    Pressure check cap and system, 15 PSI and holding. Check with engine running too. Could be other issues. Didn't want to hear that one.
    Easy does it with coolant reservoir tank. Fittings maybe brittle / cracks in unit? Bring the check book.
    Check and /or replace heater control valve. Good place for a small leak. Any leak is system leak. BAD NEWS
    Replace all hoses. New clamps. Cheap insurance, a feel good moment. Blow a hose and the ZONE may not have it. (I also add an extra large & small clamp, not tight, for trail spares just it case, fuel line too)
    Nice to have the lower stainless radiator to engine manifold. Less rust too. SHINNY
    Add the fan clutch quick disconnect fittings / hose. Make belt changes a WHOLE lot easier than a Rubik's Cube.
    Check fan clearance to shroud. A bad engine mount could blow the wind out of fan and day.
    Run proper mix of coolant. More is less.
    OH...did I forget belts.

    No guarantee to the above info. Comments free. It worked for me. Add to it, cuz I am sure I miss a lot.

    When the hood is up use that study time above to get all "JIGGY" with all the other going on's. Wiring, hoses, modules, valves, pumps, nuts and bolts.

    Running cool now, CAMO

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  9. #107
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    I found the correct, made in the USA, thermostat at a local auto parts store for the 6.2 L. It is a Stant part number 13479.
    Stant Part 13479.jpgStant 13479-b.jpgStant 13479 Thermostat.jpg
    Last edited by G3isMe; 08-05-2019 at 22:14.

  10. #108
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    Gentlemen, we have "leaf blower" engagement. Today I removed the line from the Cadillac valve and blew air through the line to engage the fan. It took quite a while and a lot of blowing to get the fan to move back and forth with regularity. I also lightly rapped on the clutch with a rubber mallet and a piece of soft wood a few times. After I did this for about 15 minutes I started the engine and unplugged the TDM. The fan engaged completely with the sound mimicking a leaf blower. I had never heard the fan on this truck sound like that before so I am pretty confident that part of my cooling problem was the fan not engaging properly. I have ordered a thermostatic switch from Kascar which should arrive soon. Hopefully replacing that will cure all of my cooling issues. Thanks again guys for all of your advice in this thread.


    .

  11. #109
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    War horses, What is the process of unsticking the fan clutch? Do you have to remove radiator stack? I think my 6.5 NA clutch is sticking, it moves a little but the fan does not make roaring sound that it used to make. Any help would be appreciated

  12. #110
    4 Star General NormB's Avatar
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    I’m wondering if your cadillac valve is bad and/or your line from it to the fan needs to be bled. If it moves a little, it should move enough, or maybe there’s some oil on the clutch friction plates.

    Just thinking/typing out loud here.

    I’m sure it’s in the manuals.
    A day without rivnuts is like a day without a Humvee mod.

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