A few months back my car (1996 C280) overheated and a faulty viscous fan was diagnosed.
The viscous unit has been replaced by the main dealer. Since then, however,
the viscous fan is ON all the time.

As I understand it should switch off when car is cold (like a cold morning start)??

The dealer agrees. The viscous has now been replaced for a third time, and still
it stays on ALL THE TIME. Is this correct??

They tell me it can't be an installation problem, as the unit is 'sealed' and self
contained, with no outside factors influencing it's functioning.

The fan bothers me because it is noisy and it affects fuel consumption.
(if it works when it's not supposed to...)

Any suggestions?

 

That's a good one. You're right. It should not be on when cold at first startup. Otherwise, what's the point???
These things are made to work that way and are usually pretty reliable. There's nothing about them more than
you say. If the dealer insists that the installation has nothing to do with it, how does he explain the fan spinning
at cold startup in the morning? It's possible that you need to switch fans altogether to remedy this. If you've already
done this, with completely new and different fans, and it still does it, I have no idea. Has to be the fan. If yours is
spinning all the time, you obviously don't have a viscous (clutch drive) fan, do you. Hmmm. Really don't know. If it
were me, I'd start looking for another brand fan or something completely different. Sorry can't help you on this one.[:@]

 

All I can think of is that the installation is to blame since this is the 3rd
BRAND NEW viscous clutch... the statistical chance of them all being
faulty? Highly unlikely...

I was wandering if perhaps the clutch can be locked somehow?? (to
protect it for instance, during transportation??) - and must be 'unlocked'
or 'activated' somehow before installation?