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Subject: Fan Clutch Tips

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Auretrvr

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Posts:28

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Iowa

03/01/2008 5:14 PM
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 http://www.thepowershop.com/fanclutch.htm 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 corner. 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.

Balrgn

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Posts:805

Registered Users
Southern NH

03/01/2008 6:53 PM
Very nice, it's alway nice to share info!

1977 Argosy 20 454 V8 Gas Southern NH Maintenance Analyst www.balrgn.com

COOPERHAWK User is Offline

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Posts:838

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East Central Minnesota

03/02/2008 10:25 AM
Thanks for posting that. I am getting ready to replace my fan clutch and it is very timely.

1985 Airstream 345 Turbo-Diesel VFW,Legion, NRA FAA Air Traffic Control Supervisor (Retired) http://www.cooperhawk.net mailto:jimcooper@cooperhawk.net "People are okay in ones and twos. After that number they tend to choose up sides and wear arm bands and berets."

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