Cooling fan freaking out?

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mturner2003

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Hello everyone. My cooling fan has recently started freaking out. It just randomly comes on and off sporadically for no reason.

My Humvee's cooling fan always came on once the temp gauge hit 200 degrees. Now, it will come on and off as soon as I starting driving down the road. Even with coolant temp not yet registering on the gauge.

Here are 2 videos I took this morning driving into work at a cool 49 degrees here in Ohio. One of them a few minutes after I left my driveway. And, another a few minutes later. Coolant still well below 200 degrees. You might have to turn the volume up but you can hear the "whooshing" effect that usually happens when the fan kicks on.

https://youtu.be/vFu8fcB4EnU
https://youtu.be/VXzCKLO9FMo

Can anyone help me diagnose this? Cadillac valve? Temperature sensor? <-- (new yellow band version installed last Dec.) Any other ideas?

I appreciate everyone's support in advance!
 
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papakb

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The sensor on the crossover pipe is the one that controls the fan, the one behind the alternator is the one that controls the gauge. There are plenty of reasons this may be happening. A bad time delay relay, a bad Cadillac valve, or a wire getting ready to fail. Take a look at the input voltage to the Cadillac valve and see what it's doing. It should be there all the time until the system wants the fan to run and then it goes away but since no voltage is the fail safe mode anything that causes it to drop out will turn the fan on. Monitoring the input voltage to the solenoid will tell you if that's the problem and you can backtrack from there.
 

mturner2003

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Ahh. Good point. I did happen to know the fail safe is full on, so it makes sense that possible a wire my be loose causing the fan to sporadically turn on and off. I'll check it out tonight and see what I can find. Thank you for your input.
 

mturner2003

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Got around to checking the rig out today. Started her up cold. Jiggled wires and harnesses. Nothing. Pulled the 2 prong connector to the cadillac valve and the fan spools up. Slows back down when connected. While still cold, I played with the throttle, holding steady at different RPMs. Sure enough, the fan does what it does in the videos. Sporadically comes on and off. Typically at mid to high RPMs. Hooked up a volt meter inline to the cadillac valve and sure enough, when it freaks out voltage drops below 24V. (Update 12-12-19, I was using a subpar multimeter for this. My nice one confirmed it DOES supply voltage) Hmm... this will be interesting to trace. I suppose I will check power at the sensor on the crossover. That is the only update I have at this time.
 
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Retiredwarhorses

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I have this same issue on a truck..,just haven’t started to work on it. My 2 trains of thought were voltage or failing PS pump.
i might go with the thermostatic switch first...but it seems to engaged only at higher RPM’s, so I’m thinking it not that.
the Cadillac valve solenoid was quite gummed up, cleaned it...no change.
have too many other trucks needing work right now.
check your voltage drop starting at the engine harness...unplug it from the thermostatic switch and rev the motor and see if the voltage drops, then move outward toward the TDM and Cadillac valve.
 
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Retiredwarhorses

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Absolutely no whine in the PS system, turns effortlessly...more inclined to think it’s a bad fan clutch, maybe even debris in the lines to the clutch. The fan isn’t fully engaged, when I unplug the TDM, it locks up fully, when accelerating it sounds half or a 1/4 engaged.
now, it’s not a terribly bad thing, as it’s just keeping the motor running cooler, not getting to over 200-220.
 

mturner2003

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All right here’s the update. Sorry for the delay.

Follow the entire flow diagram in the maintenance manual. Everything checks out OK. That’s all systems. Fan switch, Cadillac valve, time delay module, continuity in the wiring harness and components, etc.

Quick background, my fan comes on and off sporadically. We’re talking on and off a couple times within just a few seconds like the video. Well before the 215-220F temperature requirement to ground the fan switch.

I also noticed that and higher rpm’s during cruising this is when it would take place. So I disconnected the two wire harness at the Cadillac valve with the vehicle running. As designed the fan starts spinning.

Next, I hooked up my voltmeter to the wiring harness prior to the Cadillac valve and prior to the time delay module and I have a constant 27 V at all times. No matter what rpm.

But here’s the fun part. When I supply 24 V to the two wire harness on the Cadillac valve (disconnected from the rest of the system), as designed, the fan disengages. But, if I start to raise engine RPM to cruising speed’s, the fan will start up with the sporadic behavior.

So taking everything out of the equation and just simply applying voltage to the Cadillac valve, the fan will still act sporadically at higher rpm’s.

So I’m either losing line pressure at high rpm’s or something in the fan clutch is starting to go bad.

To be completely honest, there was one portion of the flow diagram that I did skip over and that was checking line pressure. 1. I truly felt it was electrical. 2. Didn’t feel like making a mess tonight, lol.

So apparently that’s next. That’s all I’ve got for now.
 
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