Cooling system questions

[Lof8]

I've been inspecting my car's cooling system lately. It runs at below half temp most of the time, but with a lot of idling the temp creeps up near 3/4.

The main hydraulic fan works so I've been looking at the auxilary fan. It comes on low speed with no troubles but never seems to click into high speed under long idling.

Theres a resistor on the front of the radiator near the aux fan. What is its function? Could this be the cause of no high speed? Or maybe its the aux fan itself that has the problem?

thanks for any insight.

[MR 325]

Your car should not need to rely on the aux fan to stay cool enough at idle. In my 85 [which is running the late model cooling system] I don't even have the aux fan and the car stays right at the half line even idling for extended periods of time.

[Lof8]

alright then, this may not be my only cooling problem. However, I'm interested in fixing this too. Can anyone enlighten me about the resistor located on the front of the radiator?

Does anyone have experience with an aux fan not kicking into high?

[86espowa]

A lot of people have had problems with their cooling systems that have me stumped.

I have been running my car without any fan for the past two weeks. I will let it idle as i quickly run inside for a few minutes, while it is at opertaing temp (right after 1/4 mark) and i will come back outside and it is fine. and this is in the heat of the southwest.

try flushing your system or something.

[jlevie]

Most cooling problems with BMWs that occur at idle will be a fault in the fan clutch or thermostat. And the first steps in solving the problem are to replace the thermostat and test the fan clutch.

[Lof8]

Well, its got a new thermostat. Its possible the fan clutch is going out.

The heating up under long idle is kind of secondary to my other questions:

Why won't my aux fan kick into high and whats the resistor near the front of the radiator do?

thanks guys

[PiercedE30]

The resistor next to the aux fan controls the aux fan speed, low speed=working resistor.
The plug on the side of the radiator is just a switch between high speed and low speed. You can pull the plug on it and jump the wires to see if both speeds work, if they do, then I would say the temp sensor is bad.

[HST]

I thought that the aux fan would only kick in when the A/C is running. As for the cooling issue, flush that bitch out with a good cleaner, and when you fill it back up, use some watter wetter.