BMW 535i 1989 tech quest -easy one I hope

[mike888]

Temp reading high in traffic , cools when driven so I figure fan has stopped. There appears to be four water temp sensors. Two located on the engine next to the inlet manifold , one at the top of the radiator with three wires coming out and a fourth on the header tank.
Anyone know which one it is that controls the aux fan ?

Thanks

[Paul Drawmer]

This is a guess...
The electric fan is to assist the airt con, and is driven by that.
Don't know if it's true for your car, but the engine fan is driven by a clutch (either visous or fan/clutch type) and it's that which has failed, so the main fan isn't driving, it's just idling.

You can test the fan clutch by leaving the engine idling when the gauge is showing it's over temp. Using a rolled up newspaper, try (gently) to stop the fan by interrupting it. If you can stall the fan, the clutch is malfunctioning.

Or.. there's a partial radiator blockage due to accualated crud. After switching oof, feel over the surface of the rad for even temps (it WILL be HOT).

Others who know more may give you better info.

[fixedwheelnut]

Look at the front of the viscous fan [facing the engine] if it is covered in oil it has most likely leaked from the viscous coupling and is knackered test it as mentioned before.
The electric fan is mainly for the aircon but will assist if the engine gets too hot, the switch in the rad controls that side.
If the electric fan does not work check it is not seized if that is ok check the resistor at the lower left side of the fan.

[mike888]

Will check it out , thanks,