How does the clutch on the fan work?

96 Vortec · November 6, 2001

This weekend Mike (silveradoman) and another friend came over to help with some minor stuff on my truck. Our friend drove his 66 Mustang over. He recently changed to a flex-a-lite fan and raved about the cooling at idle. We started talking about fans and I asked what exactly the clutch did and how it worked. We all sat there scratching our heads trying to figure out exactly how they work. Could someone please explain them to me?

ryr8828 · November 6, 2001

http://www.automotive.eaton.com/about/pressrel/980223.html

Here's a press release from Eaton about their fan clutch from 1998. Years ago a "friend" of mine used to wink at us and reach down and grab the spinning fan. I guess he could tell when the clutch was engaged. I rank him right up there in IQ with my "friend" who demonstrated the Smith and Wesson hammer drop safety to me by putting it to his head and hitting the safety, thereby dropping the hammer on a fully loaded gun. I put lots of distance between me and both of these guys. And I maintain that distance today.

ryr8828 · November 6, 2001

More information on the fan clutch, copied and pasted from a website.

Fan Clutch

The fan clutch is a small fluid coupling with a thermostatic device and controls a variable-speed fan. It ensures that the fan will rotate at just the right speed to keep the engine from overheating, and reduces drive to the fan when it is no longer needed. The fan clutch has a fluid coupling partly filled with silicone oil designed for just that purpose. When the temperature of the air passing through the radiator rises, the heat alerts a bimetal coil spring to "uncoil" or expand. When it expands, it allows just a little more oil to enter the fluid coupling, so the fluid coupling starts to rotate the fan. If the air coming through the radiator is cool, the opposite happens; the coil spring contracts, the oil leaves the fluid coupling and the fan slows. Slowing the fan when it is not needed reduces fuel consumption, makes less noise and saves engine power. Sometimes a flat bimetal strip spring is used instead of a coil spring; it bows out and in when the temperature rises and drops, letting oil in and out of the fluid coupling.

CapnDean · November 6, 2001

Just think of it as if the wind resistance "stopping" the fan from spinning.

When you are going slow, airflow through the front grille is minimal. The result is little cooling of the water that dribbles through your radiator. That's where the fan comes in...drawing air through the radiator. At highway speed - -you have plenty of cooling coming across so the fan is not needed. The clutch allows the fan to stop spinning. This is also why the fellow could stop it with his hand (NOT A GREAT IDEA). Electric fans essentially do the same thing...only they are controlled by a thermostat and a switch rather than airflow.

Nother thing - - If your fan clutch goes bad, it will usually lock up so that the fan spins all the time. This creates an awfull amount of wind noise when you are at hiway speeds.

Of course if it screws up and slips all the time you will likely overheat in stop and go traffic. And YES you can drive without a fan at all. Just avoid idling, traffic jams and keep a good eyeball on your temperature!

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