How to test the viscous clutch to make sure it is working

[Bob G ✝︎]

How to I check the fan  clutch to make sure it is working properly. I would appreciate any information especially if it is in the technical manual on line?

Sincerely
Bob Geco
1968 280SL

[graphic66]

I have always just spun them by hand. You should be able to feel the hydraulic effect in the hub. It should have some fluid resistance and not just freewheel. When I have seen ones go bad they just spun and to get back home we drilled a hole right through it and screwed a bolt in and had a direct drive fan. This was on a crap old Heap out on the trail, not a nice car.

[Jonny B]

There was a post on the forum some time ago (search on "newspaper") for another way to test the fan. Roll up a newspaper, and with the car at idle and warm, carefully try to stop the fan with the paper. I tried this on man, and the fan was working quite well. I did not see a response to the post, but this was one suggestion.

[johnd]

I have had intermittently working ones before on other cars.  Shopped around replacement ones are $40 . . .. so don't waste too much time messing with them.

johnd 

[jameshoward]

John,

Where did you see them for $40??

I have one that is suspect (and have seen the same newspaper thing) and would gladly replace it for $40 (including shipping, naturally) rather than ruin a perfectly good Sunday Times.

Link please!!!

James

[johnd]

After some shopping I think I  found one on ebay for that.  It is aftermarket but new.  Fits great.  Feels nice and tight.  I think this is the seller, and I think they have gone up some.  Still, not bad.

http://cgi.ebay.com/ebaymotors/Mercedes-220-230-250-280-300-W123-67-85-Fan-Clutch_W0QQitemZ350186823125QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item350186823125&_trksid=p4506.c0.m245&_trkparms=72%3A1205%7C65%3A12%7C39%3A1%7C240%3A1318

See also

http://cgi.ebay.com/ebaymotors/Fan-Clutch-Mercedes-Benz-200-220-230-240-250-280-300_W0QQitemZ220391134270QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item220391134270&_trksid=p4506.c0.m245&_trkparms=65%3A2%7C39%3A1%7C240%3A1318

or

http://cgi.ebay.com/ebaymotors/Fan-Clutch-Mercedes-Benz-200-220-230-240-250-280-300_W0QQitemZ250392858329QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item250392858329&_trksid=p4506.c0.m245&_trkparms=65%3A2%7C39%3A1%7C240%3A1318