HMMWV Overheat Q's and pictures

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McSpeed

Member
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Clinton, IL
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 230°F) (110°C)],
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(110°C), 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.
 

David172

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Columbia/Tennessee
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.
 

Retiredwarhorses

Well-known member
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Location
Brentwood, Calif
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.
 

G3isMe

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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.....:mrgreen: .
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/search.aspx?keywords=thermostat
 

Milcommoguy

Member
361
23
18
Location
Rosamond, CA
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
 

G3isMe

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Texas
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:

G3isMe

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Steel Soldiers Supporter
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Location
Texas
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.


.
 

ltrpd

Member
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6
Location
Columbiana, OH
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
 

NormB

Active member
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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.:?
 

G3isMe

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I am pretty much in the same boat as Itrpd. I've replaced the thermostat, the thermostatic switch, and blew 90 psi into the line from the Cadillac valve to the fan. The fan moved when blowing the air into the line after about 15 minutes of doing that. However it is now not moving very much at all when disconnecting the TDM to engage the fan. Initially the fan did produce the "leaf blower" effect but it is no longer engaging that well. Even if the fluid level was low or air was in the line, isn't the fail safe mode for the fan to default to On/Engaged so it would be on all the time vs. off, i.e., not engaged? I am still learning so my apologies upfront for the, most likely, redundant questions.
 

Retiredwarhorses

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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
I drive so many of these truck I’m able to see the differences in fan clutch operation.
what is 100% is that none seem to be identical. I have a truck or 2 that when hey engage, it’s like “****!”
clean underwear needed, and then others that just make a nice smooth transition, what I’m most concerned and my only concern is if it’s working and dropping the temperature as it should.
There are friction plates in the clutch, so normal wear is expected. If your clutch was sticking, it would stick locked closed, not disengaged and free wheeling, they fail in the locked position.
One thing I’ve seen is folks who put the fan blade on backwards...that will cause major issues.
 

Ant929

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Location
Jupiter
Do you have any idea why the fan would come on at 185? I have put two different Temperature switches and a new Time delay module. The fan is off on a cold start and as soon as it hits 185 it comes on and stays on. I have also checked it with an IR thermometer and it is truly at 185.
 
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