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Old 06-09-2002, 12:02 PM
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Join Date: Sep 1999
Location: USA
Posts: 338
Viscous Fan Clutch - Convert To Permanent On?

My 350 SDL with a 142K miles on it has what appears to be a failed fan clutch again after replacing it 40K miles ago (car at 100C can grab blades and stop at idle - turn motor off & fan continues to spin 2-3 seconds - cltuch is bad correct?) Car is running hotter than usual and everything else in the cooling system seems to check out so far.

I live in Florida so I'm thinking it might be good if this fan were converted to a constant "on" condition and just let the thermostat do it's thing. Has anyone done this? Good or bad idea? If good, how would I make the conversion and not have to worry about parts flying off?

When this clutch is working properly is the clutch engaged at 75-85 MPH when needed to cool or does it have a maximum RPM limit where it free-wheels, do the high spped electrical radiator cooling fans take over at a certain RPM instead.

Does anyone make an aftermarket fan that is clutchless?

Thank you.

Last edited by ezrider; 06-09-2002 at 12:32 PM.
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Old 06-09-2002, 02:16 PM
Ali Al-Chalabi's Avatar
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Join Date: Nov 2000
Location: Knoxville, TN
Posts: 1,837
At highway speed, there will be enough ram air to cool the car.

When you say the car is running hotter than usual, how hot is it running and under what conditions?

I personally would stick with the fan clutch doing its thing, it would consume energy and create noise if the fan were on full time.
Ali Al-Chalabi

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Old 06-10-2002, 12:40 AM
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Join Date: Sep 1999
Location: Cremona, Alta, Canada
Posts: 263
Highly unlikely the clutch has failed. They are suppose to spin freely, that is the idea of them. They will semi lockup when the air coming through the rad is hot enough. Is there any evidence of seapage from the bearing? Is the bearing loose? I would suspect a dirty rad either inside or out or both. Also, grabbing a rotating fan can be very hard on the fingers. NOT a good idea!
82 300SD 110k
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Old 06-10-2002, 03:40 AM
Col Tigwell
Posts: n/a
My experience indicates that the unit can be locked up, by just drilling a hole through the two halves, and putting a bolt with a nylock nut through the two halves.

However I would suggest, that you spilt the unit in half, carefully checking that the rear seal has not been leaking, if you open it up and it has no oil, then of course it will not be working correctly.

The seal is a fairly common size, but again my understanding is that MB do not service it.

If you find that the seal is leaking, and you can source one, then you could put a post back on the site, for help with the oil. The oil could be a moly type. your local bearing shop should be able to assist.

Most European seals, have the size stamped usually on the inside of the seal. eg 40 x 25 x 10, being 40mm OD, 25mm bore, and 10mm width, this being a typical situation.

So before I would butcher the clutch, take a little time to find out why it does not work.

My understanding is that the fan can always be stopped by grabbing hold of it. The clue to checking it, is it turning briskly when you are at full operating temperature and car is stantionary.


Col Downunder
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