Running hot

[Timm]

The cause of the over-heating is due to a lack of cooling efficiency which is why the temperature does not creep up if you put the heater on. Either the pump is not moving enough coolant, or something is restricting the flow. It could be that the impeller has failed, that does happen - sometimes the plastic impeller breaks up - and sometimes it will spin on the shaft.

Or could it be that the flow is restricted - have you been using BMW blue coolant? Other coolants or plain water will cause corrosion that may block flow. You can flush the system as described below:

https://www.meeknet.co.uk/e31/E31_Co...g_Bleeding.htm

[TexaZ3]

The cause of the over-heating is due to a lack of cooling efficiency which is why the temperature does not creep up if you put the heater on. Either the pump is not moving enough coolant, or something is restricting the flow. It could be that the impeller has failed, that does happen - sometimes the plastic impeller breaks up - and sometimes it will spin on the shaft.

Or could it be that the flow is restricted - have you been using BMW blue coolant? Other coolants or plain water will cause corrosion that may block flow. You can flush the system as described below:

https://www.meeknet.co.uk/e31/E31_Co...g_Bleeding.htm

It had some weird orange coolant when I got the car. It has been properly flushed and filled with BMW blue coolant now (twice!)
Radiator is aluminum, so is the block - how can it rust?

[Timm]

I should have said oxidize rather than ferrous rust...