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Fan Clutch testing question

jgcox6 on Sun March 29, 2009 9:47 AM User is offline

Year: 93
Make: ford
Model: f-150
Engine Size: 4.9l

I read the posting of how to test a fan clutch by one of the senior members...and here is a quote from the posting: "If it spins with a fingertip when cold, it is shot." I need to know does that mean it should take more than a finger to spin the other words it should be quite hard to spin with just your fingers? Just trying to decide if mine is really shot. I can use my finger and push on it and move the fan...does that mean its bad?

bohica2xo on Sun March 29, 2009 12:04 PM User is offline


If you push it with a fingertip, it should move. If you push it with a fingertip & it spins like a kids pinwheel, it is junk.

I happen to own a 1993 F150 with the 4.9 I6. The OEM clutch was gone by 50k miles. A new "white box" unit from autozone lasted 25k before it was unable to make any change in fan coupling when hot. A name brand aftermarket unit lasts almost as long as the OEM unit. My 150 has about 150k on it, and I have put a few clutches on it.

Be sure you have the right clutch when you buy one. They used two sizes that year, and the waterpump thread is different. Measure the hex across the flats, and be sure the replacment you pick up has the same size hex. If you have 100k or more on the OEM waterpump, I would replace it at the same time. If you replace the waterpump, take the one with the larger fan clutch thread, and get a clutch to match. Make sure you have the tools to fit the clutch & pulley, it takes both tools to do the job.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Mon March 30, 2009 7:36 AM User is offline

Knew the fan clutch on my 454 motorhome engine was okay when a stack of papers on the dining table way back blocked by the seat blew all over the place when I revved the engine to 1,500 rpm. Did I mention I was also floating around with those papers?

But if I wanted to be scientific, would have used my strobe tach on the fan, checking it's speed compared to the tach on the engine with compensation for the fan to crankshaft pulley ratio. Would expect it to be within 10%.

Fan pulley is smaller than the crankshaft pulley, so you divide it's diameter into the diameter of the crankshaft pulley and multiply the quotient time the engine speed, then you know it's working right when comparing the two tach speeds. So you don't have to guess by pushing the off blade with your finger.

jgcox6 on Tue March 31, 2009 8:10 AM User is offline

thanks for the replies for the pushing with a finger tip...i can do that with some resistance...definetly does not spin like a pinwheel. Do you have a recommendation on a fan make and model...especially since one of you guys have 4.9l Ford f-150.

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