Fan Clutch Recharged with 10,000 cSt Silicone Oil - PeachParts Mercedes-Benz Forum

EDBSO · #1 06-05-2015, 03:10 PM

The fan clutch has been showing all the traditional symptoms of having (failed) run out of fluid.

Fan blade turn freely when turned by hand.
Temperature running a bit higher in city driving.

I used a locally available 10,000 cSt silicone oil. It appears that it is a "tuneable" differential fluid for Radio Controlled cars, so try local RC shops.

Or order here.

After first removing the 4 bolts that hold the rad support in place I popped the shroud clips out as well as the the rad hold down clips.

I used an 8mm allen wrench that I taped into the end of 18" of old (1950s) thick walled copper pipe. While checking for fit I applied a bit of pressure to check alignment etc and the nut loosened with a loud "pop". After that it was finger loose and easily removed.

Similarly when reassembling it can be finger tightened to all but the last turn or so. Found elsewhere where 33 foot pounds was the recommended torque and while I have a great torque wrench there is no way that I could get it in the available space so I guessed.

Once off it was easy to drill a 1/8" hole in the fan clutch reservoir. I then tapped it with a #8 by 3/8" stainless steel screw. I then took a fresh screw and ground 1/2 of the length away.

Filling was easy. Hold the fan on a 45 degree angle and hold the bottle opening over the hole, press tightly and squeeze. Repeat to fill, stopping to let the air burp out. I got nearly the complete 2 oz bottle in.

After torqued down on the car it was much harder to turn by hand and after starting the fan obviously moved much more air.

How long will the oil stay in, who knows, others report extended success, I will advise.

bsmuwk · #2 06-05-2015, 06:46 PM

It may be too soon to ask the question, when cold does the fan turn with relative ease and start locking up when the engine gets hot?

I've heard of this being done every now and then, just never went out and actually did it - I guess you'll be the one to say.

EDBSO · #3 06-05-2015, 10:28 PM

The fan now moves lots of air when cool and at operating temperature. It stays at 80C so I haven't got it hot enough to lock it up.

With a couple of hours of city driving it is very obvious that the fan clutch failed years ago and I just didn't recognize it because it was so gradual. It can be heard running in the car when the radio is off. Not an intrusive sound but with a tuned ear you can hear it. It is not a roar.

Should have done this years ago and I suspect others should be doing it now.

Zulfiqar · #4 06-06-2015, 03:48 PM

Test the fan that it disengages at cold start after 20 or 25 seconds and that it disengages above 3500 rpm regardless of temperature.

The fan blade wheel is a destructive weapon if spun too fast.

In my experience abut 5 or 8 cc usually was enough to get it working again