Viscous Fans

[turnipsock]

My fan seems to be running all the time. Is there anyway to repair the coupling or is a replacement the only way?

Does anybody know what goes on inside the coupling?

 

[andy_k]

the fan blades will turn all the time as it's a centrifugal clutch, as the fluid gets hot it expands and "locks" the clutch. It's unusual for one to fail and work constantly, the opposite is the norm

There is no perfect way to test it but the "carrot test" is pretty effective and needs to be done in two stages

1, With the engine cold run the engine at tickover or just above and try to stop the fan with the carrot - the blades should stop easily



2, When the engine is hot repeat the test, if the fan is working properly the carrot will sliced. If the blades stop spinning there is a good chance your viscous coupling is knackered

Do not even think of trying to use your fingers to stop the fan!!!!!

some couplings can be repaired but it's not an easy job and involves refilling the clutch with a replaecment fluid, seldom more than a temporary job and I'm not even sure the Merc one can be opened up.

HTH

Andy

 

[TimN]

Easy enough to change. You will need a fan coupling spanner and don't forget it is a left hand thread. Last thing you want to do is tighten it up by mistake as the most difficult thing you will encounter is getting a purchase on the pulley.

 

[turnipsock]

Now I'm confused. I've taken the thing off already, but it was only held on by a RH allan bolt. (This is on the 320CE)

I'm driving around with the fan removed at the moment. I'll take a picture of the part later. There is a number on a red ring that doesn't match the part number that comes up on EuroCarSpares.

The bearing, that it rotates on, seems very stiff. I tried a carrot test before (using a piece of rubber hose instead of a carrot) and had difficulty in stopping the fan rotating.

 

[Sanjiv Ranchod]

Viscous Fan

I have had a similar problem on my C 280, where the viscous fan was 'weak'. The options were to replace the coupling from the MB dealer at a cost, or find an equivalent coupling from a delaer specialising in couplings, which they could match, based on the original. The other option I chose was to mhave the fluid replaced, by a specialist, using the same fluid as supplied to the viscous coupling manufacturer. I saved about 50% of the costs on a "pirate' replacement and have had no problems thus far. The coupling is back to being 'tight' again.