E39 530i aux fan, pretty much on all the time

[_Deano]

I've just started to notice that the front aux fan (the one to cool the A/C unit?) has started to come on at full speed as soon as i start the car; this never happened before. Once the fan has started (and it's loud) it will stay on for as long as the journey maybe slowing down a bit, but then picks up speed a moment or so later.
Not sure where to start looking as there is no indication (water temp gauge, touching rad pipes) that there is anything out of the ordinary. Also the A/C isn't turned on in the car.
Any ideas?

Will post a video up tomorrow, so you can see it from a cold start.

DJ

[JJM]

Hi DJ

Sounds like the Final Stage Resistor / hedgehog.

http://www.540i6.com/finalstagereplacement.html

It is quite a common issue and a 30 minute job to fix. When my one went I got a replacement from this company for about £25.

http://www.motormec.co.uk/engine.html

Cheers,

J

[_Deano]

JJM said:

Hi DJ

Sounds like the Final Stage Resistor / hedgehog.

http://www.540i6.com/finalstagereplacement.html

It is quite a common issue and a 30 minute job to fix. When my one went I got a replacement from this company for about £25.

http://www.motormec.co.uk/engine.html

Cheers,

J

Hi JJM,
Thanks for the link, but it's not the internal fan that is causing the problem. It's the fan that is just behind the front bumper.

cheers

[bababa]

If it's like the E36, the fan can be called from two areas - the AC and the engine cooling system (it can be called into operation if the viscous fan isn't keeping up with engine cooling load).

However, I think only the engine cooling system has the ability to operate the fan at the higher speed, so it would suggest it is this, rather than the AC system which is causing your fan to be permanently on.

So you have two potential culprits - the temperature switch on the side of the radiator or the high-speed relay in the relay/fusebox.

I would diagnose by pulling the connector off the radiator temperature switch; if the problem goes away then you have a faulty radiator temperature switch. If it persists then it may be that your high-speed relay is jammed on - and you can check this by subsequently pulling the high-speed relay to see if this resolves the problem.

But this is just for diagnosis - I wouldn't drive the car with either of these defeated!

Cheers,
T.

[bababa]

Again, it's another E36 resource, but I just found an article I remember reading a while back which addressed this issue...

http://www.dvatp.com/bmw/maintenance/e36/2010/01/1...

[Fox-]

bababa is spot on. I had exactly the same issue - it was the temperature sensor in the lower pipe on the left hand side of the radiator (with you facing the engine bay looking in).

Unplug it and the fan stops. Plug it in and the fan goes. It's broken. New one is a tenner from BMW. Changing it takes 5 minutes.

[Max M4X WW]

If that's true you are lucky, mine wasn't working at all and a new one was £300+!

[Fox-]

Max M4X WW said:

If that's true you are lucky, mine wasn't working at all and a new one was £300+!

Thats a different yet equally common fault.

[_Deano]

If not pulled the cable yet to test the connection, but today the fan hasn't been on much at all (self healing?)
Is there a possibility of a wire shorting out or a relay problem - if so where is the relay located?

[bababa]

If the fan seems to be coming on less regularly at the moment (especially given the fact the temperature has been a bit lower across most of Britain these last few days), I'd be even more inclined to suggest the problem is with the temperature switch (as Fox- says) rather than the relay.

Relays generally work or they don't, so it would definitely be lower down in my suspicions than the temperature switch.

ETA - can't help you locate the relay on the E39 I'm afraid, although on the E36 it's in the fuse/relay box in the engine compartment.