Mini cooper: Fan on when engine cold

[ming666]

R55 Cooper Clubman
2010, 50,000 miles

This has just started happening: Fan comes on when the engine is cold and continues to run for a while after the engine is switched off even though the engine is cold (like 45C, read from OBD as the car doesn't have a gauge!!). AC on or off makes no difference.
This symptom also started at the same time: Sometimes takes 3-4 times to start the car or it starts then dies immediately, I assumed this was the temp sensor sending the wrong information to the ecu and under-fuelling what it thought was a hot engine so I replaced the temp sensor. It made no difference. No fault codes at all on the OBD reader.

If it wasn't for the bad starting I'd think it was the fan unit but I'd like to have other ideas as that's quite expensive.

This car only has the R3 relay not the R4 as well so I assume it's a single speed fan? or are they all two speed? If it's two speed mine only works at the higher speed.

Any ideas? TIA.

[Rush2252]

They are a two speed fan controlled by the resistor. The high speed runs whenever the AC is on and also whenever the thermostat opens up.

[ming666]

Thanks
I'm pretty sure mine is only single speed. There's only one relay for the fan.
Also I can't believe the high speed fan comes on whenever the thermostat is open. The thermostat is open the whole time the car is running after it has reached temperature there's no need for the fan to be on just because the stat is open.

anyway: As a follow up to this
Yesterday I took the car into a BMW specialist place and they very kindly ran it through their diagnostics for free.
It produced a list as long as my arm of fault codes but he did say that a lot of them could have been produced when I unplugged things or removed fuses (which I have done a lot of!)
There was 2F22 500 miles ago which coincides with the problem starting and indicates the temp sensor.
He reset the whole lot and said anything that comes back is worth checking out.
The reset fixed the fan and the starting problem (who knows for how long though) so maybe it just needed a reset after I changed the temp sensor

Anyway at least I now know it's not a wiring fault.
Shout out to the great garage for doing that for nothing! BMR performance in Turners Hill (UK)

[Rush2252]

Your assumption that the thermostat is always open is incorrect. The thermostat opens and closes, when closed the fan is cooling the coolant in the radiator, once the thermostat opens the hot coolant from the motor is exchanged with the coolant in the radiator, thermostat then closes when the temp drops below its set point and the process starts over.

[ming666]

Originally Posted by Rush2252

Your assumption that the thermostat is always open is incorrect. The thermostat opens and closes, when closed the fan is cooling the coolant in the radiator, once the thermostat opens the hot coolant from the motor is exchanged with the coolant in the radiator, thermostat then closes when the temp drops below its set point and the process starts over.

I didn't say it was always open. I said it was open once the car reaches temperature. I don't know what this one opens at but typically they open at 78-85C or thereabouts. Once the car is up to temperature it's pretty much open the whole time unless maybe you live in the arctic. The fan doesn't come on until the coolant is at 105C or thereabouts so it certainly isn't running whenever the thermostat is open.