Need help understanding the HMMWV cooling circuit

[Andyrv6av8r]

So here is an update. Installed new cadillac valve and pressure gauge in fan line. Old valve ohmed 71.1, new one, 72.2; not a lot of difference so both theoretically good. Started up and cycled fan about a dozen times with pressure showing on the gauge over 100 psi with fan disengaged.



Unplugged but still showing a little pressure.



Plugged in and fan off.

 

[Andyrv6av8r]

Went for a test run down the interstate and under hard acceleration form a start, I saw 205 but it dropped down after gaining speed.




So after returning , pressures were the exact same both plugged in and unplugged. So the power steering pump is fine. Fan noise when engaged wasn't as loud as on startup but was definitely cycling. Maybe when hot it doesn't fully disengage hence the difference in noise.
Another thing crossed my mind. Late last summer I removed the armored grill from the front of my hood and it made a noticeable difference in cooling. But I still have the armored grill on top. Driving in the fall and winter the fan never cycled. So does anyone here have the armored grill on top that can tell me their normal temperature in this 80 to 90 degree weather? Does your fan cycle on and off? Maybe 200 is the normal temp for my truck.

 

[Glider]

Man I'm confused. It sounds like it is working properly. It's loud for a second at startup, runs, gets warm, then needs to run based on engine demand. I can run mine on flat ground and it will run rarely, go up a long mountain grade and it will cycle often. Hotter weather more often cooler weather less.

 

[Glider]

Man I'm confused. It sounds like it is working properly. It's loud for a second at startup, runs, gets warm, then needs to run based on engine demand. I can run mine on flat ground and it will run rarely, go up a long mountain grade and it will cycle often. Hotter weather more often cooler weather less.

Mine runs between 215 and 190ish.

 

[Milcommoguy]

Here in the 118 degree Mojave Desert, 6.2L NA, 3 speed, armored grill, 190 degree thermostat, 16 psi cap, coolant 50/50, 2200 AGL, ice tea in hand...Fan cycles on at about 220 ish... depending on all the variable ie: Loading, ambient temp, all things working the engine, etc. Give it a minute and the temp is on the way down. Fan pulls temp down to 190 ish. Give it a minute and again depending on above the cycle repeats. A small about of time or hysteresis is included between cycles.

There is a great deal of time between cycles (to be expected) here between winter and summer. 30 degree winter days, fan may cycle once in 10 miles, flat land, 55 MPH. Same condition but 115 degrees, cycle times every mile or so. Here, if the fan is on the temp is coming down. I even have a light showing engagement.

As owner, operator, chief grease monkey... I keep an eye on gauges and have never seen high temps that cooling system couldn't manage. One can watch the gauge and set a watch by it LOL.

This wasn't the case when I first dug into all the problem of ownership. Cooling system was a mess. Radiator and block cruded up, solenoid open coil, thermo switch wonky. A brand new learning curve to wrestle with. As a hobby this fit the bill. Anybody can drive one...ahh... most anybody.

If the system is cycling that's a start. Not familiar with your gauge set up. Questions here would be 24 volt, matching sender, etc. Not an die hard OEM man ... So if this works for you great. Looks better than OEM. And is plus 60 MPH a test run. WOW, my little HumV will set this race out. Haha

I have questions as to the thermostatic switch and crossover thermostat condition. The two are a balancing act to manage temperatures in my book.

All things equal...the numbers seem a bit low, CAMO

 

[osteo16]

I have an armored hood insert.. Wire mesh front grill insert.. I must be a lucky SOB because since I have had this running ( 3-4 months) my engine cooling system appears to be great.. Once I freed the stuck fan clutch with some precision whacks with the old mallet and punch..Thanks for the tip you forum buddies... But honestly to answer your question, my temp hits 210-220, fan kicks in for 10-15 seconds.. Temp drops under 200 and its good for another 10-15 mins depending on terrain and speed.. I usually only get fan kick on when climbing hills after engine has been running 10-15 mins,, My fan cycles are short and sweet, and not too often.. Sorry to here that your are having a "dilemma" but I'm sure it will work out.. Isolate the components as your are doing.. Could be anything from a freak gauge, solenoid, sticking/slipping fan clutch, intermittent power steering box, thermostat open or in backwards, or whatever.. But if its not overheating

 

[juanprado]

I went from a non armored front and top grill to both armored. Only made a 10 degree change for me and was not noticeable change in cooling system operation.

 

[Andyrv6av8r]

Thanks for the replies. I reinstalled my armored insert in the front yesterday and it didn't make a difference in temps. Still rides at 200 and the fan isn't cycling.

 

[Milcommoguy]

Just reviewed the pressure gauge photos. This is just a BIG FAT GUESS and free. What if the spring in the clutch was a wonky and the disconnect valve shown with 20 PSI static pressure was high enough not to release.

Going down the rabbit hole, CAMO

Thanks for the replies. I reinstalled my armored insert in the front yesterday and it didn't make a difference in temps. Still rides at 200 and the fan isn't cycling.

Some tum wong in da motor city. Wait till winter and ya freezes your booty shaker off.

Drive it like you stole it, CAMO

 

[Glider]

Okay so I've had a chance to look at this more closely and haven't had four beers. You show a picture saying fan off and zero PSI on gauge. Is that correct? Fan off should be around 100psi.

 

[Retiredwarhorses]

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?

that ended up being a bad Cadillac valve solenoid..the reason it eluded me was because I originally replaced it during TS and it didn’t fix the issue….I generally only replace the solenoid and not the entire unit.
once I had a buyer of the truck, I had to fix it.

 

[Andyrv6av8r]

Okay so I've had a chance to look at this more closely and haven't had four beers. You show a picture saying fan off and zero PSI on gauge. Is that correct? Fan off should be around 100psi.

Needle has went all the way past 100. I'm guessing 110 psi with fan off.

 

[Milcommoguy]

Needle has went all the way past 100. I'm guessing 110 psi with fan off.

You can guess, bet, flip a coin, get out a weegie board... bottom line is somehow your not reading the posts here or taken the time too... HERE GOES... look in the TM.

IF ALL THE COMPONENTs ARE WORKING CORRECTLY...

Normal NOT HOT
On a cool engine ie 215 degrees (but for test sakes cold start) Engine running, engine temp switch CLOSED, 24 volts being applied to TDM from temp switch, 24 Volt now applied to solenoid, your indicated plus 100 PSI (good) at the gauge location in picture, fan should be disconnected more or less "freewheeling" (Don't try and grab it)

Going hot 220 +/- degrees. ( dependant on individual OEM temp switch quality control / design characteristic and maybe engines ??)

At set point of switch design... Temp switch OPENS, Breaking flow of 24 Volts to TDM... in turn removing 24 Volts to solenoid and removing pressure, allowing clutch springs and linings to lock fan to drive belts and suck BIG air thru radiator, over the engine, thur the tunnel, raising the cab temp and rattling your ears. YEP, been there, felt that, heard that.

TDM Kickdown / switch. Should fan be engage (HOT ENGINE, NO VOLTAGE TO SOLENOID) and driver depresses throttle to the floor . A switch will close and triggered the TDM to provide 24 Volt for about 20 seconds to disconnect fan... allowing extra ponies to say pass or ease the truck / fan into water before becoming a propeller.

Note: This switch (kickdown) also signals / controls the 3L80 to down shift. 4L80e is too damm smart. TPS

Failsafe mode. Electrical disconnecting of components will place fan in the engaged state. (good to know if can't control overheating)

Again, all components fully functional and best to be OEM. DIY and hacks...all bets are off.

That's how MY fan system works. Others... I have not a clue and folding while ahead....Before mine breaks. LOL

Mr. GRUMPY and HumV are going for a COOL ride, GRUMPY

 

[Andyrv6av8r]

You can guess, bet, flip a coin, get out a weegie board... bottom line is somehow your not reading the posts here or taken the time too... HERE GOES... look in the TM.

You don't need to insult me; I can assure you that I have read every post on this thread and I understand how each component works. Glider thinks the picture shows zero pressure with the fan off (disengaged). It actually is past 100 psi to around 110.

 

[Milcommoguy]

You don't need to insult me; I can assure you that I have read every post on this thread and I understand how each component works. Glider thinks the picture shows zero pressure with the fan off (disengaged). It actually is past 100 psi to around 110.

Wasn't meant to insult. It was MY way of clearing any misunderstanding of how this system works and mostly for ME. Based on ALL of your input and fiddling around, temperatures not consistent with normal operation, leading to what if's and excessive head scratching and MY careful reading of the steps taken from the beginning to revolve (and yours were very GOOD ) one keeps circling back to "it is still busted" This can happen to anyone, We've all been there.

I got this GUT feeling were going to hear about a missing link to this story. Seriously, I want to see it on the road and remove the "Red Tag" GOOD LUCK.

Closing the hood and chilling, CAMO

 

[Andyrv6av8r]

The only thing I can think of left is the clutch itself. As someone mention before, I plan on replacing the thermostat soon as I have a new one I bought a long time ago. Just maybe it's staying open too much to let it get up to temperature? Can't hurt........

 

[Mullaney]

The only thing I can think of left is the clutch itself. As someone mention before, I plan on replacing the thermostat soon as I have a new one I bought a long time ago. Just maybe it's staying open too much to let it get up to temperature? Can't hurt........

.
A lot of vehicles off the GP lot seem to be without a thermostat.

Can only AssUMe that they were stuck shut on their last duty station - and removing was an instant fix - rather than waiting for a replacement. That way there wasn't a usable truck waiting on the sidelines for a part...

 

[Glider]

wayyy out on a limb here. Do you have the paradox by design cooling kit.

 

[Action]

wayyy out on a limb here. Do you have the paradox by design cooling kit.

LOL. Or a keyed ignition switch?

 

[Andyrv6av8r]

.
A lot of vehicles off the GP lot seem to be without a thermostat.

Can only AssUMe that they were stuck shut on their last duty station - and removing was an instant fix - rather than waiting for a replacement. That way there wasn't a usable truck waiting on the sidelines for a part...

.
A lot of vehicles off the GP lot seem to be without a thermostat.

Can only AssUMe that they were stuck shut on their last duty station - and removing was an instant fix - rather than waiting for a replacement. That way there wasn't a usable truck waiting on the sidelines for a part...

I don't think that applies here. I've had the hmmwv for almost 2 years and it used to function normally.