Cooling fan help please

[LMC]

Guys, I don't think my cooling fan is working (330 Ci). I suspected so because I was sitting idling the other day and after about 10 - 12 minutes the temp guage started to climb past its normal. I opened the bonnet and the fan was sort of oscillating ie it spun about a quarter turn then back an 1/8th then stopped, almost as if it couldn't make up its mind whether to go or not.

The fan seems to freewheel OK when I turn it (cold engine of course, I like my fingers !) so its not the bearings.

Does anyone know how I can test it, ie bypass the sensor to activate it. Then I can find out if the unit works, thus eliminating it. I don't want to be buying sensors and fans if all I need is one or t'other.

Help would be much appreciated.

[Olf]

Look up 'viscous fan coupling failure' and see if it rings any bells with your problem.

[LMC]

Ah now that is interesing...

There's an Australian web page that describes how to lock it up so that the fan turns with the engine. Then you can sit and idle - if the car stays at its normal operating temp then it is indeed the viscous coupling that is goosed.

Thanks for that

[uk68charger]

May be different on 3 series, but with my 5 series I thought same problem was due to viscous coupling but it turned out to be water pump.

Apparently, if the pump isn't working properly the viscous coupling stays cold so doesn't 'know' it needs to operate. (or something like that - others here will explain it better, i'm sure)

In the end I had new water pump, thermostat, hoses and header tank (extra stuff just to be safe) and the viscous coupling was fine. No problems since.

Also worth noting: Apparently these cooling systems need VERY careful bleeding after you've worked on them.