E46 diagnostics - please help!

[TonyRPH]

My 325Ci developed an overheating issue last year, following CCV replacement.

I took it to another garage who replaced the water pump, fan and viscous coupling (prior to this the AUX fan was working).

This improved the situation, however I've noticed that the auxiliary fan doesn't seem to switch on anymore.

I've got BMWScan140 and the relevant dongle, however I don't see any errors reported for the fan, and neither do I see any way of activating the fan to test it.

I have checked that I have 12v to the connector that feeds the fan.

Apart from INPA, is there any diagnostic tool that can test the fan and doesn't cost the earth?

P.S. The car has been on SORN hence it's not been used since October last year, but now I've decided to try and sort it out.

Thanks.

[8Tech]

If you have 12V and an earth to the fan and it doesnt run, the fan is in need of replacement. Can you rotate the fan by hand? If not, them magnets in the motor have probably corroded, fell off and jammed. No option but to replace it. If the fan does move by hand, then its probably corrosion on the brushes, may clear with a few manual spins, but a good sign its fooked.

[TonyRPH]

Thanks for that - it just seems odd that it was working prior to the water pump being replaced.

Now suddenly it no longer works.

I was hoping there would be some way to trigger it manually.

[Oneball]

The electric fan only comes on if the ecu determines the engine needs it or the ac needs it. Turn the ac on for a while and it should come on. I also think I remember that it comes on for a short period of time at initial start but could be wrong.

If you’ve got a thermostat problem the electric fan often won’t come on as the sensor is after the rad.

[TonyRPH]

Oneball said:

The electric fan only comes on if the ecu determines the engine needs it or the ac needs it. Turn the ac on for a while and it should come on. I also think I remember that it comes on for a short period of time at initial start but could be wrong.

If you ve got a thermostat problem the electric fan often won t come on as the sensor is after the rad.

The aircon hasn't worked for some time, but the aux fan still came on. My initial thought was that it stopped working because of the new water pump and viscous coupling which made the mechanical fan more efficient.

Unfortunately, the thermostat wasn't changed at the time. And your suggestion does make me wonder if the thermostat is sticking.

[Sardonicus]

Sounds like an auto trans variant that front rad mounted fan will work no longer as your A/C is offline low speed cooling is dealt with by the viscous fan only that the manual trans M54 engine powered cars dont have fitted

[TonyRPH]

Sardonicus said:

Sounds like an auto trans variant that front rad mounted fan will work no longer as your A/C is offline low speed cooling is dealt with by the viscous fan only that the manual trans M54 engine powered cars dont have fitted

It is indeed an auto transmission. But I'm confused...

The aux fan was working (despite the A/C not blowing cold). Does the fan operation depend on A/C pressure? If A/C pressure is low, will that prevent the fan from working, whether or not the A/C is switched on?

The A/C clutch hasn't activated for months because the system has a slow leak - but the aux fan still came on....

Hence my confusion.

[Sardonicus]

Well if it did it wont need it providing the viscous fan is operating correctly (more than capable) if you get the AC repaired then worry about it , personally I would if its fitted I want it working

[TonyRPH]

A new fan and coupling has been fitted. Therefore I can only assume it's a radiator blockage or <shudder> head gasket.

I tested with one of those colour changing fluid kits over the expansion tank, and the fluid didn't change colour, so I'm hoping the head gasket is ok (I ran the engine for a while to get it up to temperature) - I realise there could still be a head gasket problem however.

I guess I'll have to take it to a specialist.

[Oneball]

TonyRPH said:

Sardonicus said:

Sounds like an auto trans variant that front rad mounted fan will work no longer as your A/C is offline low speed cooling is dealt with by the viscous fan only that the manual trans M54 engine powered cars dont have fitted

It is indeed an auto transmission. But I'm confused...

The aux fan was working (despite the A/C not blowing cold). Does the fan operation depend on A/C pressure? If A/C pressure is low, will that prevent the fan from working, whether or not the A/C is switched on?

The A/C clutch hasn't activated for months because the system has a slow leak - but the aux fan still came on....

Hence my confusion.

The electric fan will only come on if the ecu thinks it is required. There is a separate sensor for it in the bottom rad hose. If the viscous fan wasn’t working before and is now it’s probable that in this weather it doesn’t need the electric fan as well. You can check that coolant is going through the rad by feeling if the bottom hose is getting hot.