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Old 07-28-2006, 01:57 PM
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Join Date: Jul 2006
Posts: 41
1991 350 SDL Fan Clutch

Is there an accurate method of checking the engine fan clutch to see if is working properly? I am concerned that it might not be working as it should while on the highway.
Thanks in advance,

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Old 07-28-2006, 02:01 PM
rrgrassi's Avatar
mmmmmm Diesel...
Join Date: Jun 2006
Location: Royse City Tx
Posts: 5,122
Do a search for "fan clutch". There is a visual way, with the engine running, turn it off. If the fan keeps spinning, then the fan clutch is toast. It should stop either immediately, or with in one revolution.

70's Southern Pacific #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 133K miles-replaced the other '06 that quit after 300k miles. (did not catch the bad cam in time)

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Old 07-28-2006, 10:07 PM
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Join Date: Oct 2001
Location: around Charlotte NC
Posts: 583
watch at shut off


I had an 87 SDL that I was concerned the fan clutch was too loose. It was replaced once and still seemed loose. At shutoff even when very warm ( 100* +/- on the guage) the fan would spin to a count of "9"... That is thousand 1, thousand 2... up to 9. The temp never got above 105* and only for a short time under heavy load. So in reality the clutch may have been ok and I was too chicken.

I did the toyota fluid refill and probably overfilled it. Once again when hot, did the shut off and it stopped in "thousand 1" or less. Over a year it leaked a bit and went to not quite "thousand 2".

The tighter fan meant about a 5* change in readings on the dash gauge. Also a quicker reduction in temp after a highway run, then stuck at an exit light, then pull away. The tighter fan reduced temps much more quickly. It was a bit noisier in all operating conditions.

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Old 07-28-2006, 10:27 PM
babymog's Avatar
Loose Cannon - No Balls
Join Date: Jan 2006
Location: Northeast Indiana
Posts: 10,765
Just replaced mine on my 190DT, loose bearings seemed too much risk.

Reading the manual, I believe it was to run the engine around 3000rpm and the fan should come on between 190-195F, I'd have to re-read. The manual also said that the fan would not exceed a certain RPM in any conditions, I believe it was around 3500rpm?? So it is apparently centrifugally self-limiting, explained to me why it didn't roar like my LandRover fan at higher RPM. A fairly quiet fan really IMO for a cast-metal fan.

- Jeff Miller

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