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Fan viscous coupling

It's one of those which should vary the drive to the fan as it gets hot. But appears to run at the same slow speed even with the gauge going high in heavy traffic, and the aux electric fans have cut in. At speed the temp is fine.

I removed the coupling and tried heating the 'clock' spring with a hot air gun and saw the valve move round, but the resistance to turning the shaft by hand remained the same. If it were working normally, would the resistance increase at what is effectively very low revs, ie turning it by hand? Or only at much higher revs?

Reply to
Dave Plowman (News)
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The unit should lock up practically solid as the heat increases. Almost certainly I have a few of these fans in my garage. I will have a look tomorrow and let you know.

mrcheerful

Reply to
mrcheerful

My fathers BMW used to stiffen up as the temperture increase and spring unwound. If you heated it with a hairdrier it would eventually lock almost solid. Even so the electric aux fans would eventually kick in in a queue.

Reply to
Chris Street

Firstly you should have a locked coupling at cold start after the oil has settled into both parts. Holding the engine at ~2500rpm you should hear it roaring for perhaps 5-10seconds afterwhich it should decay to the fan pretty much freewheeling with no drive at all.

Heating the coupling should then progressively relock it.

Sounds like yours is fubar'd. Quite common.

Tim..

Reply to
Tim..

I have got two viscous fans from earlier SD1 They have a hole through the middle and are secured to the pump by a nut in the middle on the radiator side. They do not have a visible clock spring, the mechanism is internal (different manufacturer I guess) but if the fitting is the same they should fit. Lakeside Essex free to collector.

mrcheerful

Reply to
mrcheerful

or were you talking about the bmw?

mrcheerful

Reply to
mrcheerful

Yes - earlier SD1 viscous couplings are like this. On the EFI engines they have the standard left hand thread 'cap' nut fitting and are temperature sensitive.

Reply to
Dave Plowman (News)

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