Cooling system fans and clutches...

Back in the old days the cars came from the factory with fixed fans with 4 blades or thermostatic fans with usually 5 or 7 fan blades made of aluminum, , on the water pump. Today, it seems that there is a variety of options available, so I started looking at the options for my Chrysler. This research is applicable to all brands of cars, since the fan blades all operate on the same principle, and they almost all have similar parts. The choices are now non thermal, standard duty thermal, and heavy duty thermal clutches. I had to do a lot of digging to find out exactly what the difference was between all 3. I also learned while doing this research, that there is a vast difference in the quality of the various brands available, even though they all appear to be the same. On this page is where you will find the information to decide what you actually need for your application. It appears from what I have read so far, that the Hayden brand of fan clutches have the best track record of reliable consistency of manufacture.
Fan clutches go bad for only one reason... the seals fail with age, and the viscous fluid in them starts to leak out. When they loose fluid, then they no longer work, and the result is insufficient cooling. To test your fan clutch, use the following procedure. I got this information from the 1963 Chrysler service manual.

Silent Flite Fan Drive

• The fan drive consists of a rotor driven by the shaft which is secured to the water pump flange. The rotor is enclosed by the housing to which the fan is bolted. The housing is mounted on the shaft through permanent sealed bearings.
• A nominal clearance space is maintained between the housing and th rotor. The housing is partially filled with a silicone fluid and the shear resistance of the fluid between the housing and the rotor provides the driving force rotating the fan.
• The fan drive has been designed to provide the necessary driving force to maintain cooling at low speeds and to limit the top speed of the fan at higher engine speeds.

Overheating

• If the fan drive operates below its minimum design speed, engine overheating may result at slow vehicle speeds. Test as follows:

1. The cooling system must be at room temperature for testing.
2. Mark one fan blade with whiter or yellow chalk or crayon.
3. Attach a timing light to the engine. Set the engine speed to 1700 rpm and then adjust engine speed until the fan blade mark appears stopped by the timing light.
4. The drive should be replaced if the engine speed at which the fan appears stopped is below 1600 rpm for TC-3 or TY-1 air conditioned models or below 1550 rpm for TC-1 or TC-2 air conditioned models. DO NOT ATTEMPT TO SERVICE THIS ASSEMBLY.

Excessive Fan Noise

• If the fan drive fails to properly limit the top fan speed, excessive fan noise may result. Test as follows:

1. Observe the engine speed at which the timing light appears to stop the fan as in "Overheating."
2. The drive should be replaced if the engine speed at which the fan appears stopped is above 1850 rpm for TC-3 or TY-1 air conditioned models, or above 1800 rpm for TC-1 and TC-2 air conditioned models. DO NOT ATTEMPT TO SERVICE THIS ASSEMBLY.

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While these instructions are specific to the Chrysler models, the basic principles are the same. I checked some of the GM shop manuals that I have, and none of them give any specifics, other than to replace the part in the event of overheating as a possible remedy.

that sounds a lot better then the let it warm up and if it coasts for a long time after you shut it off change the clutch, I was told. notice the 1800 rpm. that's 70 mph in a late model car. my how times have changed.