E46 cooling problems...

[CIS121]

It's a 330 petrol 2003 which I've owned for about 4 years, looked after and have have never had an issue with.

I'm using it about twice a month currently and took out during the deep freeze last week and whilst always it's got upto normal temperature within 5 minutes it didn't leave the top of the lower red band. I took it home after a few miles.

I tried it again last night and the same thing:
Engine isn't leaving the top of the red band (unless I sit in traffic then it goes upto normal temperature)
Also oddly, the heating inside the car isn't very hot.

It seems like coolant is flowing but not as much as it should be so I was thinking the water pump may be failing, but this doesn't match the symptoms of overheating and there are no odd noises.

Any ideas?

[Jobbo]

Thermostat stuck open, perhaps?

[ghibbett]

+1 ^^^^ Sounds like this

[phelix]

Failed thermostat. Replace it. And consider doing the water pump at the same time.

[CIS121]

Great - thanks for the advice folks. A thermostat stuck open makes perfect sense. Looking on the web it seems a reasonable job to take on myself so I'll get one ordered.

Phelix - re: replacing the water pump too - what would be the reason for this. Has it got a life similar to the thermostat or is it one of those things that's so easy to do when the coolant's drained that it would be worth doing at the same time?

[phelix]

E46 water pumps seem to last for between 50 and 80K miles - it's a "while you in there" repair. If nothing else check it by removing the serpentine belt and see how much play there is in the bearings. It should be minimal. Mine sounded like a bucket of bolts at 60K miles but with the tension of the belt no play could felt. Removing the belt revealed the bearings were well knackered.

On automatic cars there's a fan attached to the front of the pump; if the pump fails catastrophically the fan can go into the rad taking that with it.