w124 Viscous fan operation...

[silverback mike]

Hello again folks,
Moving from r129sl's good advice in my other thread, I'm intrigued.
Does the Viscous fan cool the engine directly from engine temperature or from elsewhere when switched. The only reason I ask is my temperature gauge doesn't work and I don't want to overheat the old girl.
If it's in traffic, will the viscous cool the engine, so in effect the only thing missing is the fact I actually don't know what the temperature is doing??

I'm going to fix it with a new sensor hopefully tonight but will be sat in traffic tonight for a little prior to fix.

( I only picked it up yesterday so it's an unknown prior )

[r129sl]

Me again...

As I understand it, the viscous fan coupling or clutch engages when it gets to a certain temperature and disengages when it falls below that temperature. There is no electrical input, just like the thermostat. It is not switched. I assume it relies on its proximity to the engine and radiator and that the temperature of the fluid within it changes according to how much heat the engine and radiator are radiating.

Engines which rely on an electrically switched fan for cooling generally fail safe: i.e. in the event of a bad signal the fan will switch on.

At the risk of stating the obvious, the engine cooling fan is behind the radiator and is belt driven; the electric fan or fans on the front of the radiator are for cooling the air con condenser.

[OldBuoy]

Viscous fans can fail mine did. They have a bimetallic strip which engages when hot. One test is to get the car really really hot and if at idle you can stop the fan with a rolled up newspaper it's failed.

Even if it had failed I doubt you will overheat the car in this weather unless something else is wrong.

I replaced mine when I noticed in city centre traffic 30C outside and A/C on full blast temp was creeping up towards the red.

If the sensor doesn't fix it, it could be the instrument cluster. Try reseating the main cluster connector with some contact cleaner or sometimes it's a dry cracked solder joint inside the cluster.

Edited by OldBuoy on Wednesday 8th October 18:36

[r129sl]

I ought to add that I have three spare clusters if you need one: theres a chance at least one of them will be right.

[silverback mike]

Thanks for all the help It appears to have been fixed when I replaced the sensor, it's running a bit over 80, is that normal?

[OldBuoy]

That sounds fine. It will go up and down (unlike a modern which uses a damped do da to show a stable temp and not worry the driver) If it goes over 120 it's time to worry.

[silverback mike]

Thanks Old buoy, it does seem to fluctuate a bit. I'm taking it through rush hour traffic through the centre of Bristol this afternoon fingers crossed