W140 Engine fan always on...

[richard300]

Hi, i have purchased a 1996 S280 and thought it a bit 'noisy' i noticed this morning that when i started the car from cold with the climate control switched off, the fan (the one between the engine and radiator) came on strait away... I know it gets hot here in South Australia, but i cant imagine it's supposed to do that!

 

[markjay]

I don't know if cars in South Australia have their radiator fans permanently on by design, and I don't know how it is supposed to be on your specific model either - but a common setup is for the radiator to have a thermostatic switch which closes an elecrtical circuit when the coolant reaches certain temperature.

The circuit then feeds the fan relay.

If either the thermostatic switch or the fan relay are faulty, then the result could be what you describe.

You can try disconnecting the wires on the thermostatic switch, if the fan still runs them the issue is likely to be with the fan relay.

Both are cheap enough to replace, but note that replacing the thermostatic switch involves some loss of coolant.

And remember to take care not to work in the engine bay when the fan is running or might come on.

 

[coalville126]

Wouldn't the fan be engine driven, so turn whenever the engine is running?

Perhaps the viscous coupling needs looking at if it's locked-on, i.e turning at engine speed when cold.

 

[markjay]

See also:

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[carat 3.6]

The m104 engine in your s280 use's a viscous coupling to drive the fan, it will turn when ever the engine is running.

As said above, the coupling can lock up.

Start the car from cold, then see if you can stop the fan using a rolled up newspaper.

 

[richard300]

Yeah, it did stop with a newspaper..... Sounds like nothing to worry about then?

I was thinking it didn't spin until a certain temp or even a couple of further stepped temp related speeds.

Thanks.

 

[carat 3.6]

Yeah, it did stop with a newspaper..... Sounds like nothing to worry about then?

Sounds like it's working as it should.