Forums banner

1 - 1 of 1 Posts

Beading on My Wagon
692 Posts
Discussion Starter #1
The cooling fan on (I think) all inline engines is mounted onto the water pump shaft. There's a temperature-activated clutch that engages the fan when the air coming through the radiator gets above a certain temperature.

The same or similar fan clutch unit is used on Merc's, Scoobys, some jeeps etc etc.

My E39 overheated a little for the first time ever, and after investigating I found the fan clutch was freewheeling all the time, never engaging. This is easy to check: with the engine running, carefully put in a thin stick or a rolled-up piece of paper into the fan. If you can stop the fan, there's a problem. Also, in a working fan clutch there should be some resistance to rotation even with engine off and cold; in my car the fan would go for several revs if I gave it a spin.

The problem is that over time the oil in the fan clutch leaks out. A replacement fan clutch is well over E100 for a decent unit, meh!

I did some research and I am happy to say I did a completely successful repair, as follows:

For the oil, you need 60mL+ of 3000cS silicone oil, this is honey-thick. It's used in shock absorbers on model cars. Order two bottles from MSD models, about E12 to your door. Here's a linky, the guy there is ****:

Then get a syringe from your local junkie or pharmacist, a 10mL one is perfect. You don't need the needle. Sand down the diameter of the tip of the plastic nozzle so it fits nicely into the hole in the clutch unit.

Then remove the fan from your car. It came loose foe me first time by slipping on a 32mm spanner and whacking the spanner, hard, with a lump hammer. No need for special tools. REVERSE THREAD! Leaning into the engine bay you hit the spanner left-to-right.

Next remove the two rivets/screws that hold the plastic fan shroud in place, one either side. Pull up the shroud about 200mm and you can get the fan out. Bring the fan to a bench.

Next, remove the bimetal strip by folding flat the two raised tabs at each end with a small screwdriver, rotate the strip a little and it pops out. It'll be held by a blob of silicone rubber, too.

Next, remove the metal pin and the green seal. I reckon this seal was leaking a little in mine; but I got 14 years out of it so far and I didn't bother replacing it.

Next, suck 10mm of 3000cS silicone oil into the syringe, press the nozzle of the syringe hard into the hole, and shoot. Put a total of about 60ml in. I heated the clutch unit with a hot-air gun and spun the fan lots of times, this helps get the oil in. Take your time injecting the oil, a little gets expelled back each time you remove the syringe.

Once you've about 40mL of oil in you'll start to feel some resistance to spinning. If you put too much in, the unit will be a little too viscous and the fan won't completely disengage - but no harm.

When the oil is all in, re-assemble the pin & seal. Put the bitmetal strip back in place and bend up the four tabs. Apply blobs of silicone cement to the ends of the strip, leave to dry, & then give the unit a good wash to get rid of leaked oil.

Then stick the fan unit back into your car and take 'er for a spin.

Total cost: about E12 for the oil, and 1 hour's labour.

I took some photos during the job :smile:



1 - 1 of 1 Posts