Viscous Fan Clutch

[Martin Sullivan]

Hi all,

How stiff should the viscous fan clutch be?
I have it out of the car, if you hold the big 32mm nut and try to turn the fan it feels smooth but incredibly stiff. If you turned it one or two full rotations your fingers get tired! I'd of thought it should be a little more free spinning then this?

Thanks
Martin

 

[t-tony]

Is that a new or nearly new fan clutch Martin? If it is then I would say it's as it should be, it may become easier to turn when it's warm as it is filled with a wax like substance. As long as it is smooth to turn I would be happy with it.

Tony.

 

[Martin Sullivan]

Nope, it’s the original so 20 years.
I found a YouTube video of an American cousin which suggests my fan clutch is as it should be:

View: https://youtu.be/51noZBn3Pvw

 

[t-tony]

Nope, it’s the original so 20 years.
I found a YouTube video of an American cousin which suggests my fan clutch is as it should be:

View: https://youtu.be/51noZBn3Pvw

It's done well then, how much mileage has it done? Some people do change these out of caution when they've done a lot of miles. Me, I wouldn't unless it started to show signs of wear, ie play or noise.

Tony.

 

[Martin Sullivan]

It’s a bit over 70,000k, not sure where exactly. 2000 model.
I expected it to spin more freely which is why I asked.

I was tempted to swap it regardless but it’s another expense and I’ve got a lot of them on the Z3 at the momentbut if it’s recommended to replace it I would.
Ideally I’d replace most of what I’m touching but it would be a money pit.

Martin

 

[t-tony]

That would be around the mileage people replace them at Martin, another thing which a bad viscous coupler can do is impart vibration through the plastic fan blades which sometimes then break apart and make more damage. Yes, it can become a money pit but sometimes it is saving in the end.

Tony.

 

[Nodzed]

Just bear in mind that was not a BMW viscous and they are not all the same. Mine is 3 years old and wont spin that easily and didnt from new.

 

[Andyboy]

They can be stiff when cold, and then loosen up after a few seconds. This will cause the fan to roar on cold start up but die off after 5 secs or so. If the coupling still looks clean and silvery then the oil hasn't leaked out.

 

[swamper]

Has anyone just removed it and ran it without?
I say this as on the M it has the air con fan and an oil cooler the size of the QE2.
Even when ran hard on hot days it has never showed any signs of struggling

 

[t-tony]

I think some people just fit a fan switch with a slightly lower “cut -in” temp. Wayne. They call this the “fan delete?”

Tony.

 

[Nodzed]

Has anyone just removed it and ran it without?
I say this as on the M it has the air con fan and an oil cooler the size of the QE2.
Even when ran hard on hot days it has never showed any signs of struggling

Viscous Fan Delete Modification

Removed the Viscous fan today and changed the fan sensor switch for an 80 / 88. Didn't have to remove the rad cowl just undo the nut and slide up and out happy days. No leaks no overheating on a good hard run, needle in the middle :) in fact it never ran in the middle with the viscous...

zroadster.org

Yep, read through to post #6 though, and if you want to do it dont buy the switch, you can mine FOC

 

[swamper]

Viscous Fan Delete Modification

Removed the Viscous fan today and changed the fan sensor switch for an 80 / 88. Didn't have to remove the rad cowl just undo the nut and slide up and out happy days. No leaks no overheating on a good hard run, needle in the middle :) in fact it never ran in the middle with the viscous...

zroadster.org

Yep, read through to post #6 though, and if you want to do it dont buy the switch, you can mine FOC

Just read it and its a fair point.
She'll say standard as I've never had a an ounce of problem with her like this...it was just a thought..

 

[Nodzed]

Just read it and its a fair point.
She'll say standard as I've never had a an ounce of problem with her like this...it was just a thought..

Neither did I until a hot day long steep twisty road, loads of RPM and not much speed.

 

[t-tony]

They were made the way they were for a reason, don’t you think?

Tony.

 

[Andyboy]

They were made the way they were for a reason, don’t you think?

Tony.

Yes. If it didn't need a fan, BMW would not have fitted one. They absorb very little power (if any) when not locked up.

 

[t-tony]

It’s just the viscous liquid inside which keeps it rolling until it locks up. Hence you can stop it spinning using a rolled newspaper or other method.

Tony.