Viscous fan always running

[mrscalex]

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.

 

[Ianmc]

Is the sensor OK?

 

[mrscalex]

Is the sensor OK?

The fan itself isn't connected to one. It's got a viscous clutch that engages when a valve opens controlled by a bi-metallic strip.

 

[andyglym]

The fan itself isn't connected to one. It's got a viscous clutch that engages when a valve opens controlled by a bi-metallic strip.

Mine ran permanently before I refreshed the entire cooling system including the viscous fan, still runs permanently now

 

[t-tony]

Can you try cooling it (in the freezer for a few minutes) and see if that releases the drive?

Tony.

 

[mrscalex]

Can't believe I don't know this but. Is the viscous fan meant to run slowly all the time? Then just go faster as the car warms up? Or should it be fully halted and not start up until the car is warmed up?

Don't have another running Z3 at the moment to check

 

[mrscalex]

Mine ran permanently before I refreshed the entire cooling system including the viscous fan, still runs permanently now

It doesn't seem to affect the car warming up. But then the temperature gauge is designed to show in the middle over a wide range. So it could be running on the cool side of normal.

 

[mrscalex]

Can you try cooling it (in the freezer for a few minutes) and see if that releases the drive?

Tony.

Haven't got anything to lose by pulling the strip off the back and working the valve. That's the first thing I check on a domestic radiator when they don't warm up. That's what's under the thermostat knob.

 

[andyglym]

It doesn't seem to affect the car warming up. But then the temperature gauge is designed to show in the middle over a wide range. So it could be running on the cool side of normal.

Same, warms up as quick as any other car I've had and the needle sits bang on where it should be.

 

[Rudyrov]

Before I removed mine for a fan delete, my fan ran slower than the engine and seem to lock up as the engine idled and got hotter. When not running the fan could free wheel but had a significant amount of drag. I removed the fan because I installed a larger 3-row radiator and electric auxiliary fan along with a lower temp sensor for the OEM electric fan in front. That was 2 years ago and I have had no issues and live in Phoenix, AZ.

 

[andyglym]

Viscous Fans Explained

Thought this may be helpful to some. Viscous Fans Explained Viscous fan couplings are used on vehicles (cars and trucks) with inline engine positions, mainly rear wheel drives. These fans are needed at slow speeds and while idling. A faulty fan can cause an engine to overheat while idling or in...

zroadster.org

 

[mrscalex]

Viscous Fans Explained

Thought this may be helpful to some. Viscous Fans Explained Viscous fan couplings are used on vehicles (cars and trucks) with inline engine positions, mainly rear wheel drives. These fans are needed at slow speeds and while idling. A faulty fan can cause an engine to overheat while idling or in...

zroadster.org

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?

 

[Barron]

On my 2.8 the fan runs constantly at a slower speed, in hot weather it engages gradually until it runs at the required speed. When it runs at full speed you can hear the difference.

 

[Ianmc]

The fan itself isn't connected to one. It's got a viscous clutch that engages when a valve opens controlled by a bi-metallic strip.

Ahh - my M44 has a sensor (not of course viscous fan) to turn on the electric cooling fan (which doubles as the aircon fan). Had some issues a few years ago and a new sensor sorted it. Controlled by a "bi-metallic strip" must be a wonderful thing!!

 

[Duncodin]

On my z3 the fan runs all the time. When cold it's just freewheeling. There's just enough friction in the clutch to move it but can even be stopped with my fingers.

 

[t-tony]

That is how we used to test them. People also use a rolled newspaper, remember them?

Tony.

 

[mrscalex]

Clearly been away from Z3s too long... agree now these things should spin slowly when cold and faster when hot - slow or fast. For some reason my head was thinking either stopped or fast. I've spent a lot of time recently rebuilding the front end on my lad's Citroen C2 which has an electric fan and is stopped from cold. My head has clearly been polluted...

Makes a lot more sense now why 2 behaved in the same way...

 

[Synclare]

.

 

[Andyboy]

They can be locked up briefly when cold - that's quite normal.

 

[Mike Fishwick]

The fan will always run at about engine speed when disengaged and idling, due to the viscous drag if the fluid in the coupling. You cannot mistake it when engaged - it sounds like a fire syren! Mine only engages when idling on hot days on high mountain passes, where the air is thin, but it soon disengages after driving away. The aircon condenser fan normally does all the work.