Fan stuck ON

[gcbennet]

It appears to me that my engine cooling fan is now stuck fully engaged, creating a very audible 'whirring' noise, especially at higher RPM's. I'm afraid that if i take her onto the highway at 55+ MPH the plastic blades won't be able to handle the stress and might come apart or something. Am i right to be worried? Seeing as the cooling system on the humvee seems to be somewhat of an over-engineered enigma to me, what could be the cause(s) of the fan being stuck on? The pump is new and the fluid level seems to be ok...

 

[FASTNOVA]

I would not worry about the fan coming apart unless there is some visible damage to the fan. Can you spin the fan by hand with the engine off?

 

[gcbennet]

Good to know. The fan is in good shape so i won't worry. No, the fan won't spin by hand with the engine off.

 

[Augi]

The fan shouldn't spin by hand with the engine off. Follow the hose from the face of the fan clutch up to the cadillac valve on the firewall. Disconnect it from the valve and apply 100psi compressed air to the hose. While you are holding the pressure on, see if you can turn the fan. If not, the fan clutch needs work. Could be as simple as whacking it with a mallet to free it up.

If the fan clutch actuates via air, then there is a problem with the hydraulic system. Maybe check the time delay module. If it's unplugged or messed up, the fan will be always on.

Augi

 

[FASTNOVA]

If it is a HMMWV then either the fan controller is bad or the connections to and from the fan could be bad or even the fan clutch, but I would check all your connections first. If your truck is an H1 it has a viscous fan clutch and you cannot spin it by hand then it will need to be replaced.

 

[Retiredwarhorses]

Very rarely...and I mean very rarely is the fan clutch bad, leaking yes, bad no.
it generally one or more of 3 things...listed in priority.
1. Bad time delay module
2. Bad or clogged Cadillac valve.
3. Clogged lines

If the fan is stuck, replace the TDM, if that done fix it, remove and blow compresses air through the Cadillac valve.
the first 2 fix 97% of non-working fan issues.

now, there is the 4th thing that can happen....if the clutch has been engaged for many years that way, the clutch plates inside like to seize to the housing, now you need to remove the fan clutch and beat on the back of it with dead blow hammer to unseized them...I have personally seen NOS fan clutches out of the box that will not pass 100psi air test...but end up getting a beat down to unseize them.

oh, and remember, you could very well have all of items 1-3 wrong....so start with the easiest, item 2, I say this cuz most folks ain't got a TDM layin around....but the bad TDM is the no.1 reason, just had this on a customer truck last week.

 

[papakb]

When the cooling system is functioning the fan clutch will actually move about 1/4" forward and backwards indicating the clutch is functioning. By applying air pressure to either the hose from the Kysor-Cadillac valve on the firewall shelf or by applying it directly to the fitting on the radiator shroud you should see the fan move. With no pressure you shouldn't be able to turn the fan blades. With pressure applied they should move easily by hand. This checks the clutch only. The time delay module (TDM) next to the Kysor valve is triggered by the kickdown switch on the side of the injector pump and is used to make the clutch freewheel when fording so that it isn't being driven when entering the water. This can cause the fan blades to shear off. This is the module that controls the Kysor valve functioning. It's a high failure item. Lastly the temperature sender on the water crossover manifold sends a signal to the Kysor valve when the engine reaches 220 degrees turning on the fan to cool the engine back to 180 degrees. They can also fail but are easy to replace. This is not the sender that the temp indicator used, that one is in the side of the engine block behing the alternator.

Kurt

 

[gcbennet]

Ok, so i applied compressed air to the fan clutch and it works as it should. So without just swapping out parts hoping the problem goes away, how can you tell if it's the TDM vs the Temp Sender that's the culprit? If either of these units fail do they automatically default the fan to stay engaged to prevent the engine from overheating?

 

[TedG]

The temp sender on crossover can be bypassed with jumper. By connecting/disconnecting the jumper the fan clutch should activate/deactivate. Regardless, the temp sender and the tdm are reasonably priced and spares should be kept. Good luck!

And yes, fail mode is to keep fan clutch engaged to cool engine. Just do not go into fan blade deep water or many bad things will happen!

 

[dukecola]

The temp sender on crossover can be bypassed with jumper. By connecting/disconnecting the jumper the fan clutch should activate/deactivate. Regardless, the temp sender and the tdm are reasonably priced and spares should be kept. Good luck!

And yes, fail mode is to keep fan clutch engaged to cool engine. Just do not go into fan blade deep water or many bad things will happen!

Would you have the GM part numbers for the temp sensor and the TDM?