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Auretrvr 03-01-2008 09:24 AM

Clutch Fan Tips
My clutch fan locked itself up during a recent trip and does not freewheel when the engine is cool. Makes a LOT of noise. I found the following tips when browsing a GM Motorhome forum and thought it would be worth sharing...

I thought the part about proper right-side-up storage would be valuable info!
.................................................. ....................................................
How do I know if my Fan Clutch is working?
The Wiley Fan Clutch by Chuck Arnold

From time to time some motorhome owner will call me and say that he needs help because his
transmission won't shift out of second gear. Hearing this complaint, I usually ask "Is this motorhome new
to you?" Often the response is that the person has had the coach only a short time. Usually the rig is not
equipped with a tachometer (rpm gauge) and the owner or driver is misinterpreting a loud noise they are
hearing as being excessive engine rpm. I ask them if the noise goes away when they go downhill or when
the motor is cold. I ask them if it is worse or starts when they go uphill. If they say yes to these
questions, then all that is occurring is that they are hearing the normal sound of the fan clutch doing its
intended job.

The Fan Clutch is a device which permits the engine to avoid wasting horsepower by sucking cooling air
through the radiator when it is not needed. Once the motor is hot enough to need more cooling than is
provided by the normal flow of air caused by moving down the road, the fan clutch engages, causing the
fan to spin, creating more air flow to cool the engine down. Fan Clutches contain a heat-activated valve
and a special silicone fluid which permit the fan to freewheel up to a certain temperature and then to
lockup and move much more air above that temperature. This action reduces noise, saves gas, and
makes more power available to the wheels under lighter load operation. Fan clutches can be engineered
to come on at specific temperatures. Most tow vehicles and motorhomes have fan clutches which
engage when the air coming through the radiator is between 200 and 205 degrees. If you are standing
next to a running engine and the temperature is rising through the 200 degree area you will notice a
significant change of the amount of air being moved by the fan when the Fan Clutch turns on. It will seem
like a switch turned the fan on. One second the clutch is off and the next you will hear the noise and
notice much more air. (A very few clutch fans come on gradually rather than quickly)

It is a good idea to make a point of being aware of what your fan clutch sounds like and when it turns
on. Know by outside temperature, steepness of hill, amount of load, and reading on your dash
temperature gauge when it should turn on. As time goes on you may encounter a fan clutch failure or
some other problem which may lead to engine overheating. If you no longer hear the familiar sound of
the fan clutch engaging when it should, you can predict problems with overheating just around the

You can recognize a failed fan clutch in a number of ways. Look for excessive play in the bearing on the
clutch shaft and for evidence of the silicon fluid leaking out. If you inspect the front of the clutch
assembly with a light and mirror and see a greasy substance around the thermostatic spring a failure is in
progress. If the motor is at operating temperature and running at 2500 rpm or so and is quickly shut off
while someone watches the fan and the fan spins more than 4 or 5 seconds the fan clutch is bad. The
Fan Clutch does not have to be engaged for this spinning test. You can carefully cause a controlled
overheating of the engine by blocking the radiator with cardboard and monitoring the temperature while
idling in park with the brake on. If you are measuring the air temperature behind the radiator with a
thermometer and the temperature gets above 210 degrees without the Fan Clutch engaging and a
noticeable increase in air flow occurring, the Fan Clutch is bad. Be very sure to watch this procedure
carefully and remove the cardboard when done. You could ruin your engine if you forgot to remove the
cardboard. Some Fan Clutches are noisy when cold and quiet down when they warm up a bit. As long
at the Fan Clutch works properly at higher temperatures this is nothing to worry about. Be sure to avoid
the moving belts and fan. Most mechanics can remember a careless moment when they almost were
injured by the spinning fan. Stories of lost hands and fingers are a grim reminder to be very careful
around machinery.

It is very important to note that the handling of new Fan Clutches and used ones removed for other
repairs is critical. All new Fan Clutches come in boxes marked with a "This Side Up" arrow. Fan
Clutches which are not stored correctly before installation may never work properly. If you get a new
fan clutch and distrust how it has been stored, it is a good idea to let it stand on your shelf in the proper
orientation for 24 hours or so to avoid trouble. A used fan clutch which is taken off for repair of other
engine components must be stored in its normal running vertical position until it is reinstalled or it will not
work properly again. I learned this at a Delco-sponsored air conditioning school.

I was one of a hundred or so mechanics in the class who were embarassed to learn that we had been ruining every Fan
Clutch we had ever removed. If you have worked on engines and noticed occasions when you had
overheating occur after a repair in which the Fan Clutch was laid flat on the floor for a few days, you
have had this experience too.

Know your Fan Clutch. Observe it doing its proper job and treat it right when servicing, and your travels will go better during the RV'n part of your life.

ArtStream 03-01-2008 09:33 AM

Thanks Auretrvr!
Great info:)

Had I only known about this 7 years ago:o


Fyrzowt 03-01-2008 09:37 AM

Good informational post!

cooperhawk 03-01-2008 09:40 AM

My fan clutch is also locked up and I am just waiting for warmer weather to replace it.
I have also been told by an Isuzu mechanic that if the clutch is locked so the fan cannot free wheel, it will actually caues the engine to run warmer than usual.
Sounds strange though. Seems like the extra air would make the engine run cooler.

FreshAir 03-01-2008 08:48 PM

Electric fan clutch
My very first car was a 1948 Ford. I got it in 1954. Installed on it was an ELECTRIC fan clutch, thermostatically controlled. I do not ever remember having any overheating problems during the 5 years I had it. Off course, being young I had to play with it. I rigged it up with a switch on the dash to be sure to ensure a little advantage during the ocassional street drag 'challenges':innocent: . What happened to the electric clutch idea? I replace todays clutches every 2 or so years.

overlander63 03-01-2008 08:52 PM


Originally Posted by cooperhawk
My fan clutch is also locked up and I am just waiting for warmer weather to replace it.
I have also been told by an Isuzu mechanic that if the clutch is locked so the fan cannot free wheel, it will actually caues the engine to run warmer than usual.
Sounds strange though. Seems like the extra air would make the engine run cooler.

The engine has to work harder than it should to force the air through the radiator.

bkahler 03-02-2008 04:52 PM

Definitely an interesting post on how to deal with the fan clutches.

So far ours seems to be working but my long term plans are to replace the mechanical fan with 2 electric ones. Seems to be the method of choice for a lot of people.

Great post, thanks!


Auretrvr 04-10-2008 07:26 AM

Fan Clutch Installed...
Cost $78 at NAPA. I placed some kraft paper in front of the fan to protect the radiator, but there was plenty of room to maneuver and it went pretty smoothly.

The article about the danger of improperly stored fan clutches may be obsolete. The instructions with mine said that the fan would recover from being stored upright and would work fine after a little bit--and that's what I saw with this one.

A big relief in the noise department!

Alumatube 05-29-2008 02:18 PM

What can happen when a fan clutch engages inappropriately? I just had mine replaced on our Dakota, and it engages a lot when it should not (at starting, initial take-off, and taking off from a light or stop sign). It seems to work correctly otherwise. I have to go on an 1,800 mile trip starting tomorrow, the dealership did not order the part in to fix it (I took it back in enough time) because the foreman wanted a "second opinion" from the guy who did the work. He assured me that there would be no problem on my trip (What!?! He originally said he wasn't sure of what could be causing the problem so he wanted a second opinion!).

What else would make a fan clutch engage like this? And will it hurt my truck on a 3-day, 1,800-mile trip???

This makes me very nervous, but I really have no choice. :(

Susan :)

gypsychris 06-01-2008 07:17 AM

Our fan started to be always "on"... any tips? what should I do? Thanks

richinny 06-01-2008 07:43 AM

vehicle? engine? electric or clutch?

gypsychris 06-01-2008 12:09 PM

1989 345 LE with the Chevy 454 . AM not sure what you mean by "electic or clucth?"

The way it all started:
We were driving, and the fan would come on and off (as it should) then suddenly it just went into a really "high" gear -sounded twice as loud and stayed there the whole rest of the trip.
A few days later, the same thing happened....

Now it seems on, and loud, all the time....

bkahler 06-01-2008 04:52 PM


You're definitely going to have to replace your fan clutch. I'm fairly certain you can get the clutch from most good parts houses. Its something I haven't as yet had to replace on our 310 so I can't give real good advise. I know there are a bunch of posts on the forum about replacing it.

I'm kinda guessing here but I'm pretty sure you can replace it by working from inside the motorhome (which is good because you can run the roof top A/C while working!). You'll have to lay on top of the engine and work mostly by feel. I believe there should be four bolts holding the fan to the clutch and four more bolts holding the clutch to the water pump.

I always carry and nice soft mat that I can lay on top of the engine. Makes it a lot more comfortable to work that way.

Hopefully someone will chime in with more specific directions.

Good luck!


gypsychris 06-01-2008 09:17 PM

hey Brad, you mention "water pump". do you know where the water for that pump is? I found a black container near where the washer fluid container is...could that be "it?" what kind of fluid goes in there?


Also, if anyone has any more advice etc ... could it be a fuse? could it be the thermostat? Where are these?


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