W210 Fans Running With Engine Off

[MeanRedSpider]

I guess it's the same as this http://www.mbclub.co.uk/forums/showthread.php?t=66094&highlight=fans

The fans run with the engine off. The local Merc garage can't/won't look at it for a week.

Any guidance? What are potential root causes?

Thanks

Richard

 

[Dieselman]

The fan control unit can fail, possibly due to water ingress, and the fans then run full time.
It's controlled by the engine water temp sensor and the A/c pressure sensor.

 

[MeanRedSpider]

Cool - thanks. Is there any risk (apart from overheating, obviously) of running the car with the fan disconnected? The local Merc dealer (the next nearest is 120 miles away) can't look at it for a week and the local garage can't diagnose the fault.

 

[ringway]

If your car does only short runs you'll get a flat battery because of the over-running fans.

I have this problem on my Omega and after turning off the engine I sit and wait until they fans have stopped. If they run for too long, I have start up again and after a while turn off the engine again and they seem to stop.

I know a guy who had a new BMW with this problem also.

 

[MeanRedSpider]

The twin electric auxillary fans are now disconnected and I'm running it on only the main, engine-driven fan. The engine temperature seems fine - I just don't want to unwittingly cause a problem. Don't need the aircon in the Highlands at this time of year and there's rarely any traffic to speak of so there will nearly always be normal airflow.

 

[Dieselman]

Is the car a petrol or diesel.? If it's a diesel it doesn't really need any fan at all.
The AC fans should normally only operate when the AC is running and not for general use, the viscous fan is more than capable of keeping the engine cool.

 

[welland99]

Is the car a petrol or diesel.? If it's a diesel it doesn't really need any fan at all.

Do Diesels run cooler then? My instinct would have been to guess that diesels run hotter than petrols because of the need for heat and pressure to combust the fuel.

 

[Dieselman]

Much, much cooler due to better thermodynamics requiring less fuel to make greater motive power.

 

[MeanRedSpider]

Is the car a petrol or diesel.? If it's a diesel it doesn't really need any fan at all.
The AC fans should normally only operate when the AC is running and not for general use, the viscous fan is more than capable of keeping the engine cool.

Yup - diesel. I do a bit of towing of my race car so I'll get them sorted before that