Viscous fan always running

[Nodzed]

Thanks. I read that after original post and it's where I saw the fan run from cold at 20% of engine speed. Which got me thinking it's always meant to run? Or is that just on a Z3M, as Nodzed has and that's a bit different?

It will always run Rob it will just get faster as the temp rises and more cooling is needed and slower when it's not.

 

[mrscalex]

Thanks both. Clear now. Definite lapse I didn't remember this myself.

 

[Stevenod]

I know viscous fans shouldn't run all the time and should only come on when required. My 2.2 was on permanently from cold. I thought it might have been something dumb I did while changing the radiator but it was handled carefully and kept upright. On reflection I suspect it had been doing it before I started the work. I swapped it for a spare and that also runs full time from cold.

Have I just been unfortunate here and need to keep trying spares (can remove from another car if needs be) or are darker forces at work? I'll buy a new one if required but don't want to spend pennies unless I have to.

Just 'cos a picture (or video) paints a thousand words, for anyone wondering if their BMW viscous fan is about right, watch this excellent video through.

View: https://www.youtube.com/watch?v=RDuGsDUiXQw


My own fan is probably about the right stiffness. The video shows I can't properly tell until it has been spun up on the car to return the viscous oil to its reservoir, but my fan shows something like melted plastic (or maybe an epoxy-glue bodge repair?) has oozed from between the big 32mm nut and the viscous clutch body and set. Not having that. New part on order.

 

[Mike Fishwick]

Not all viscous fan clutches have concentric rings - my original clutch simply used a pair of flat plates, running close to each other. Here are mine after about 70,000 miles, when the bearing had worn and permitted contact between the plates.

Also - the fins are not there to dissipate heat, but to absorb it and prevent the clutch from disengaging until the air from the radiator has fallen to a reasonable level.

 

[Nodzed]

Also - the fins are not there to dissipate heat, but to absorb it and prevent the clutch from disengaging until the air from the radiator has fallen to a reasonable level.

Really. Thought that was the job of the bi-metal actuator. They are cooling fins Mike.

 

[Nodzed]

Just 'cos a picture (or video) paints a thousand words, for anyone wondering if their BMW viscous fan is about right, watch this excellent video through.

View: https://www.youtube.com/watch?v=RDuGsDUiXQw


My own fan is probably about the right stiffness. The video shows I can't properly tell until it has been spun up on the car to return the viscous oil to its reservoir, but my fan shows something like melted plastic (or maybe an epoxy-glue bodge repair?) has oozed from between the big 32mm nut and the viscous clutch body and set. Not having that. New part on order.

Good video.

 

[Duncodin]

My Viscous fan always turns even when the engine is cold. But it's just freewheeling. I can stop it with my fingers (Don't try this at home kids)

When the engine is hot I can hear the difference in noise from the engine bay when the fan is engaged.

 

[Pond]

Viscous fans are soooo last century.
When I got my Z3 I was amazed it had a fan from the 1920s. So much so, I was looking for the square spindle on the front to put the cranking handle in.

I have owned many, many cars since 1985 and can't think of any other with a 'mechanical' cooling fan. Luckily mine has a/c so has a 'proper' fan aswell.

 

[Andyboy]

Really. Thought that was the job of the bi-metal actuator. They are cooling fins Mike.

Mike is absolutely correct.

The fins absorb heat in the engine bay to expand the clutch and lock it up.

Depending on type, the viscous coupling will also engage from stone cold and release after a few seconds.

 

[Nodzed]

Mike is absolutely correct.

The fins absorb heat in the engine bay to expand the clutch and lock it up.

Depending on type, the viscous coupling will also engage from stone cold and release after a few seconds.

Manufacturers would disagree with you.

 

[Andyboy]

It has cooling fins on the front and the rear.
The idea is that the rear ones soak up engine heat to lock the clutch and the front ones do the reverse.

That’s why the coupling engages at standstill or slow traffic, but releases once cooler air passes over the front of it.