Temperature Control Problem

[preacha]

Hi All,

I've got an '89 520i (England), that's the E34 with the M20 engine, and I have a problem with it's engine temperature control.

It's a little strange, when I get above 35mph it moves from halfway to over 3 quarters. Speeding up to get more air on it doesn't cool it down and neither does pulling over (sometimes this makes it heat up).

Have flushed the system and replaced the thermostat, BMW report that all is well with the other parts, they couldn't work out what it was (hence the new thermostat).

I did notice the plug that goes into the radiator's wires looked a little out of place. Does anyone else have my model that can tell me which wires are meant to go where? The plug is on the driver's side of the engine bay and has 3 wires in it. Purple/Grey(currently closest to back of car), Brown (currently centre) and Yellow/Black (currently closest to front of car).

Any help you can give me on this would be appreciated.

Cheers.

[shogun]

you mean driver side U.K. (=passenger side U.S.), so that should be the connection for the aux fan at the radiator?
Have you tested the aux fan? Just pull the connection at the rad and bridge the connections, 1 is for low speed and one for high speed.
But the aux fan is usually not required when you go higher speeds, even not the visco clutch. And I can imagine in the U.K. it is not very hot now.

[DaveVoorhis]

The aux fan is really only needed when the A/C is on, and definitely not in the UK this time of year. Non-A/C cars don't have an aux fan. The aux fan low-speed resistor is burned out on mine, hence no aux fan action, and I have no problem with heating -- the needle stays dead centre in all conditions.

Have you checked the radiator for salt damage? The fins will rot off and turn to aluminium sand, thus reducing cooling effectiveness. Has the coolant been checked for exhaust gasses, which might be indicative of a failing head gasket? Have the hoses been replaced? They can collapse internally and obstruct coolant flow.

[DaveVoorhis]

I did notice the plug that goes into the radiator's wires looked a little out of place. Does anyone else have my model that can tell me which wires are meant to go where? The plug is on the driver's side of the engine bay and has 3 wires in it. Purple/Grey(currently closest to back of car), Brown (currently centre) and Yellow/Black (currently closest to front of car).
Which leads are front or back depends on the orientation of the plug, which could be anywhere -- the sensor screws into the radiator. However, the plug can only fit in one way. You can unplug it, turn on the ignition and verify the aux fan works by bridging brown-purple/grey, and brown-yellow/black. In one position, the fan should run slowly, in the other it should go fast.