E30 M3 New fan Fitted, But...

Just a thought, could it be a dodgy relay?

Before you try anything else I would check to see if the fan has been
wired up incorrectly when it was manufactured!

A couple of weeks ago was helping Richard Baxter trace some problems
with the fan on his car:

As with yours the fan had seized and was blowing the 15A low speed
resistor. He changed the fan for a brand new unit but stangely the 15A
fuse kept blowing. In addition when the car got warmed up the fan
struggled to keep the engine running down at nominal temperature. We
did loads of tests on the circuit and everything was fine, so we thought
the fan must be faulty so we did some checks:

When taking measurements from the high speed and low speed
terminals on the harness side connector, everything was correct.

We then did a bench test on the fan and connected a power supply
directly to what should have been the low speed and then the high speed
terminals - and guess what they were reversed, hence why the low speed
fuse was blowing (as it was running the high speed fan) and why at higher
temps it was actually the lower speed fan cutting in- so the car could
never cool properly!

Comparing the old fan with the new one we confirmed the wires were
reversed on the new unit and so switched them over. (Very easy to do,
you unclip the connector block, switch the pins over and clip it back
together).

Did the above and fan worked perfectly - although it really was the last
place you would check as you just dont expect faulty wiring.

So there you go, check the wires on your old fan and the new one, if they
are different swap them over and it should work ok.

Richard has contacted BMW about this as we thought it could be batch
problem and result in quite a few cars suffering.



Edited by Rob L

Another thing to check is that the wires are correctly fitted on the temp switch on the thermostat. When the wiring is repaired, quite often the high & low temp wires are refitted in the wrong way to the connector ! causing exactly the same probs as above.

Here is the correct wiring for the fan plug

Pin 1 Ground , brown wire from fan , brown wire to loom.

Pin 2 High speed , Red wire from fan , Black wire, blue stripe to loom.

Pin 3 Low speed, Black wire from fan, Black wire with green stripe to loom.

I will post a diagram of the plug on the 'stat housing soon.

Regards

Phil

p.s. had a similiar  experience a few years ago when BMW had a batch of E28 M5 gearknobs which had been stitched on the the gaiter 90deg out of sync. I re - ordered 5 times until I recieved one which was made correctly !

Edited by 286bhp