Need help understanding the HMMWV cooling circuit

[Andyrv6av8r]

I will try to keep this as short and understandable as possible. About a month ago I noticed that my 1045A2 temp was going up to 200 degrees and staying there and the fan wasn't cycling on and off. i did the normal check of unplugging the TDM and it was engaged all of the time. Took the clutch line loose. applied 100 psi of air and it cycled fine. So I assumed TDM or cadillac valve. Luckily I had a new cadillac valve from a while ago so installed it. No change. I ordered a new TDM, installed it, and it worked for about 2 days and melted into a stinking pile of goo. It got interesting real quick after that. With nothing to lose, I reinstalled the old TDM. Still engaged but no meltdown. So I ordered another new TDM. And here is where I get lost. From a cold engine to around 190 degress, the fan cycled about a dozen times while unplugging and plugging it back in. But as soon as I drive it, back to being fully engaged. After the first drive I ohmed out the cadillac valve: o ohms so it's shot. So as of now until my new cadillac valve comes in, the 2nd new TDM and my original cadillac valve are in place. And it works without fail until I drive it and it gets over 190, the locked engaged. As soon as it cools down, works as advertised. I have unplugged the fan kickout to eliminate that sticking on( not engaged fan) without any change. Oh, and I replaced the temp switch and tried jumping it with no change. So my grand finale question is, What could make the fan stay engaged above 190 and not disengage? Sorry for the long, confusing post!

 

[Action]

You stated that you are doing all of this because your fan didnt kick on at 200???
It doesnt kick pn until about 220.
I think them TM states up to 240 or 250 is normal operating temp. At what temp does your guage leave green?

 

[Mullaney]

I will try to keep this as short and understandable as possible. About a month ago I noticed that my 1045A2 temp was going up to 200 degrees and staying there and the fan wasn't cycling on and off. i did the normal check of unplugging the TDM and it was engaged all of the time. Took the clutch line loose. applied 100 psi of air and it cycled fine. So I assumed TDM or cadillac valve. Luckily I had a new cadillac valve from a while ago so installed it. No change. I ordered a new TDM, installed it, and it worked for about 2 days and melted into a stinking pile of goo. It got interesting real quick after that. With nothing to lose, I reinstalled the old TDM. Still engaged but no meltdown. So I ordered another new TDM. And here is where I get lost. From a cold engine to around 190 degress, the fan cycled about a dozen times while unplugging and plugging it back in. But as soon as I drive it, back to being fully engaged. After the first drive I ohmed out the cadillac valve: o ohms so it's shot. So as of now until my new cadillac valve comes in, the 2nd new TDM and my original cadillac valve are in place. And it works without fail until I drive it and it gets over 190, the locked engaged. As soon as it cools down, works as advertised. I have unplugged the fan kickout to eliminate that sticking on( not engaged fan) without any change. Oh, and I replaced the temp switch and tried jumping it with no change. So my grand finale question is, What could make the fan stay engaged above 190 and not disengage? Sorry for the long, confusing post!

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Wonder if you could get some benefit out of a hand held temperature gauge?
Squeeze the trigger and it takes a reading.


You could evaluate temperatures like the wall inside your house. (compare to the house thermostat)
You might compare anything else that has a thermostat - and see if you can match to the readout of the hand held gauge.

THAN, walk out there and zap the radiator from in front of your parked truck.
Does it match the electric dash gauge? Most of the military gauges are marginal at best.

Maybe that will be your problem maybe?

 

[BLK HMMWV]

Mine doesn't come on until 220, shuts off at 200.
I thought this to be normal.

 

[Milcommoguy]

Make no sense to me based on the story. Here's what I extracted and know (just barely).....

Gauges are notorious for inaccurate readings. When you get a good set working (gauge and sender) count your lucky charms. Not really that bad... but be aware of a wonkie components. This is just an instrument circuit and has nothing to do with fan operation.

Static test of fan clutch... 100 PSI to the clutch GOOD. (who does that ??) 50 psi should do it and in-system up to 160 psi) Since we're all about getting all oiled up... check pressure coming OUT of Cadillac valve (valve open / valve close) engine running. Wonkie PS pump ??

Them darn "OHM's"
Valve resistance check. 68 Ohms is the middle of the road +/- 10 GOOD. That's not a lot... so a GOOD meter that is zeroed out and an eagle eye should work. Digital takes the guesswork out. Advance test: Check resistance from each lead to case. Should be an OPEN / infinity, if not bad, or at least MEG OHMS.

Always check old parts and new to be sure of what one has. No fun going in circles. Check the thermostatic switch too. It is the "heart beat" to the whole system.

Best do the OHM thing to new switch in a pot of hot water with cooking thermometer (digital ?) a few times. Bring it up to temp looking for an "open circuit" and note temp. (really who does that, lol) When back in the rig... recorded reading should match in dash gauge pretty darn close to fan ON temp. See what we're doing here??
OK , say it with me ........who does this stuff ???

Remember... fan RUNS with the LOSS of voltage to the valve. It's a "fail-safe thing" Wonkie switch action and back to being dizzy.
Quality QEM blue tag is my choice !!! YEA.

DumB TDM.
Operation is to provide the 20 seconds to grab some extra ponies to pass or tippy toe into the water. Thermostatic switch circuit just passes thru. But GOOD call on the input to it from the kick down switch. That could mess with the logic big time. Wouldn't know to swim or get out of its way.

How's the coolant, radiador, belt/s, pump flow and block. Any signs of rust, clogged up and wonkie stuff floating in the system?

MULLANEY...With the BIG YELLOW LASER GUN (nice) making the wackie cat chase it. LOL

This is going to be a wonkie good one, CAMO

OH... Did you check your grounds ??

 

[Retiredwarhorses]

If Your temp is always low, your thermostat is stuck open…

 

[Milcommoguy]

If Your temp is always low, your thermostat is stuck open…

Yea... and that too. Wonkie thermostat. That could do it.

BUT but but... all the other problems. Shorted then changing solenoids, smoked TDM...get to 200 degrees (going in the right direction) day later fan sticks on. Changes parts like a card dealer change decks in Las Vegas and is not a luck parts changer.

If the fan is stuck on it will be hard to get any reasonable engine temp out of it and never cycle correctly. Your RIGHT Thermostat TOO.

OP story, for me is a little hard to follow along with all the monkey motion going on. Just saying ... it's up, then down, on then off, did this, then that.

It's OK, soon should be better than new. Parts on the way $$$ Don't forget the thermostat too.

Running hot and cold here and past my bedtime, CAMO

 

[Andyrv6av8r]

Thank you for the replies but I think I have confused some of you. My fan used to come on at 215-220 and run until 190. Now after engine temp goes up to around 200, it won't go any higher because the fan won't disengage.

I know it's hard to follow but here is more:

I have an aftermarket mechanical gauge that has been very accurate for the last 2 years. I ditched the electric one day one, don't trust them.

I have checked with a temp gun, fairly close, definitely not hotter than gauge shows.

I have a ground kit installed also and all grounds are tight.

I have a new thermostat but not sure that will have an effect on a fan not disengaging.

When reaching 200 with the fan engaged, I have jumped the temp switch which should disengage the fan. It doesn't.

 

[Mullaney]

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. Deleted stuff above this line (TM)
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MULLANEY...With the BIG YELLOW LASER GUN (nice) making the wackie cat chase it. LOL

This is going to be a wonkie good one, CAMO

OH... Did you check your grounds ??

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Absolutely Milcommoguy!

Cats and Dogs will chase that red dot until they get tired
Figured finding a big ugly yellow gun might attract attention in the post.

Seems like Andy already has one of those and a real mechanical gauge on the truck too.
Better than the average for sure.

 

[Milcommoguy]

OH BOY... So today we have a new Andy. I wish I had a bright light and the little room with Sgt. Joe Friday and Ofc. Bill Gannon... LOL

SUSPECT - CONFESSION REPORT - STATEMENT

I have an aftermarket mechanical gauge that has been very accurate for the last 2 years. I ditched the electric one day one, don't trust them.
That's OK. Thought of doing it myself. GOOD IDEA for the truth and fun to watch in go down with engine off.

I have checked with a temp gun, fairly close, definitely not hotter than gauge shows.
Not sure what suspect if referring to. Engine temp and gauge are tracking, taking in to account small errors in placement, alignment, etc. GOOD

I have a ground kit installed also and all grounds are tight.
That was a trapping question from CAMO to see if suspect read to the end.

I have a new thermostat but not sure that will have an effect on a fan not disengaging.
Suspect "'ANDY" stated above. Unclear if thermostat was in engine or his pocket. If installed backwards would / could be a problem. Not showing signs of running hot. Might block off top of radiator "cardboard" and front of truck to see if you can get a rise out of it. Alway good to ruff up a rig.

When reaching 200 with the fan engaged, I have jumped the temp switch which should disengage the fan. It doesn't.
Good clue. Do you have voltage at this location ? With proper working solenoid / valve, TDM, good PS pressure, fan clutch it should with 24 Volts.

Where did you find this thermostatic switch and was it checked out? It would be hard to reach operating temp with the fan running all the time. Any chance the clutch is hanging up?

Further investigation with the Multimeter / lie detector would provide a little more data to rule out a gremiln. All the Packard connection fitting up nice? Rig up some wires to the solenoid's two pins and 24 volts to energize a GOOD valve, bypassing TDM and switch. Should disengage fan.

I'am going to refer to the day shift to dig in.

A little more community service to get out of HumV jail, CAMO

 

[Andyrv6av8r]

Further investigation with the Multimeter / lie detector would provide a little more data to rule out a gremiln. All the Packard connection fitting up nice? Rig up some wires to the solenoid's two pins and 24 volts to energize a GOOD valve, bypassing TDM and switch. Should disengage fan.



A little more community service to get out of HumV jail, CAMO

I actually did straight wire the caddy valve at the very beginning just to be sure it was functioning and it was. I know it is working as I can unplug and replug ( if that's a word) the 2 or 4 connector on the TDM and the fan engages/disengages. I still suspect a possible weak coil on the solenoid (cadillac valve) getting weak when hot. Or another thought was to install a pressure gauge in the fan clutch line to monitor for a weak power steering pump when hot.

 

[REF]

I seem to remember a post from Retired War Horse some time back that may fit your situation. I Think he had a unit that functioned fine when sitting still but with RPM the fan would stay on, Like when driving. If I remember correctly it turned out to be a failing power steering pump, Pump would lose pressure at RPM and allow fan to stay on.
Does this ring any bells Steve?

So to answer ( What could make the fan stay engaged above 190 and not disengage? Sorry for the long, confusing post!) Warm fluid in a weak Pump?

 

[Glider]

I had cooling fan that ran all the time. Previous owner had bypassed the Cadillac valve. I ordered Cadillac valve and temp sensor. Installed them both properly. Fan would disengage one time from cold start and them come on and not go off. I was about to start looking into the clutch fan for problems but called one of the online HMMWV vendors(I think black dog customs) for a little advice on fan clutch. Everything was new except time delay. He said I likely had a faulty temp sensor, that there had been a bad batch that would not reset at proper temperature. I bought another new sensor but from a seller he said had genuine parts. With new temp sensor all worked properly. My .02

 

[Andyrv6av8r]

I had cooling fan that ran all the time. Previous owner had bypassed the Cadillac valve. I ordered Cadillac valve and temp sensor. Installed them both properly. Fan would disengage one time from cold start and them come on and not go off. I was about to start looking into the clutch fan for problems but called one of the online HMMWV vendors(I think black dog customs) for a little advice on fan clutch. Everything was new except time delay. He said I likely had a faulty temp sensor, that there had been a bad batch that would not reset at proper temperature. I bought another new sensor but from a seller he said had genuine parts. With new temp sensor all worked properly. My .02

I replaced my switch also. Determined it wasn't the problem because if you jumper the temp switch leads, the fan should disengage. Unfortunately mine doesn't. Thanks for the idea though.

 

[Milcommoguy]

Here's the simple book for free. Chapter 1. First three pages. Circuit drawings and wire numbers... The whole dealieOh. Let us know what you come up with.

https://gear-report.com/wp-content/uploads/2017/03/HMMWV%20A1%20Troubleshooting.pdf

This can't go on forever, CAMO

 

[Andyrv6av8r]

Here's the simple book for free. Chapter 1. First three pages. Circuit drawings and wire numbers... The whole dealieOh. Let us know what you come up with.

https://gear-report.com/wp-content/uploads/2017/03/HMMWV%20A1%20Troubleshooting.pdf

This can't go on forever, CAMO

My new Cadillac valve came today so I hope to eliminate the weak coil theory.

 

[Milcommoguy]

My new Cadillac valve came today so I hope to eliminate the weak coil theory.

Check it for resistance like I stated above. Compare with old one just for knowldge fun. Note PROPER port connections. Note what you have now BUT connect as shown in the TM...unless you "got this"

Can't wait like it's Christmas Day ??? With all the fussing past days and to add more fun...might run that pressure test on the output side to eliminate power steering pump issues. Let fluid warm up a bit. Any braking or steering issues? Dextron II or III fluid per TM.

Read the free manual to follow the system flow. (refresher... big test tomorrow, LOL) I know this has been a doozie fan problem for you. (me too)

Standing by for a full report and your final thoughts, deduction, guesses ?? CAMO

GOOD LUCK and some pictures too.

 

[Andyrv6av8r]

Check it for resistance like I stated above. Compare with old one just for knowldge fun. Note PROPER port connections. Note what you have now BUT connect as shown in the TM...unless you "got this"

Can't wait like it's Christmas Day ??? With all the fussing past days and to add more fun...might run that pressure test on the output side to eliminate power steering pump issues. Let fluid warm up a bit. Any braking or steering issues? Dextron II or III fluid per TM.

Read the free manual to follow the system flow. (refresher... big test tomorrow, LOL) I know this has been a doozie fan problem for you. (me too)

Standing by for a full report and your final thoughts, deduction, guesses ?? CAMO

GOOD LUCK and some pictures too.

I hope it's a weak coil when hot but my gut feeling is a weak pump.

 

[Milcommoguy]

delete

 

[Milcommoguy]

I hope it's a weak coil when hot but my gut feeling is a weak pump.

I read where you applied voltage and all was good. Fan DISENGAGED. If one of the TDM had a "melt down" I bet you have an intermittent "shorted or shorting" solenoid coil. Multimeter and REAL data to figure out problem or just keep "shot gunning" from the wallet.

IS this a TEST? I HOPE not. CAMO