On Sunday my 03 Mini Cooper S developed a cooling issue.

The car has run fine for a number of years and never lost any water / overheated. Just the odd small top-up of coolant. The coolant has been changed regularly and never any issues afterwards.

After a short 3 mile motorway drive with no issues I pulled into a car park. The temp gauge shot up, the car boiled over and the header tank started banging and hissing. The radiator fan was cutting is a normal.

Firstly, I assumed the worst and thought it was the head gasket. However, there are no milky signs on the oil dip stick or oil cap. I know this is not conclusive proof but I don’t have the chemical tools to test.

I managed to slowly get the car home.

I decided to rule out any airlocks, apparently the Cooper S is prone to them. I drained the system and fitting a few thermostat for good measure. The car did the same as above. However, this time I had more time to look. The top radiator hose was normally pressured and was hot, bottom hose was Luke warm. I took the radiator off and flushed it and white bits came out. At this point I assumed it was a blocked radiator

I fitted a new radiator, bled the system and it’s still the same. Still no milky signs in the oil so I still have my fingers crossed.
When bleeding the system the heater was on hot and the blowers on full as described in the manual. However the air was cold even though the car water temp up was hot and the gauge was in the normally running position.

At the moment I think it’s a blockage. Even if the head gasket had gone I don’t think that would stop the heater getting hot.
To avoid spending more money I was going to get to the heater matrix and find the pipes to see if any water is getting there and returning. If I can, I was going to try and by-pass the matrix by joining the in and out pipes together to see if the car runs normal and rule the matrix in or out.

I don’t think it’s the water pump but open to comments on that.

Any help would be welcomed before I amid defeat and assume it’s a head gasket / head issue.

Cheers Ash

Wouldn't it be cheaper to get the head gasket tested rather than going to the expense and time of messing with the heater matrix ? And I thought even if the heater matrix was blocked your engine should still run and cool fine, as the matrix is a bypass circuit ( I may be wrong though).

[Edited on 14/5/14 by wylliezx9r]

What makes you think the water pump is ok?

At the moment I was just going to try buy passing the heater to see if it makes any difference.

I would need to get/buy the tools for testing the head gasket and the car wont really move under its own steam and i don't want to risk over heating it by driving it to and from places.

I'm just stumped as to why a faulty head gasket would cause the heater to stop working.

More investigation is required.

I've not fully ruled out the water pump. I just thought it might be the least possible chance, simple device not a lot to go wrong. Maybe i was being naive on that.

I'm planning to taking the water pump off and have a look before i spend any more money chasing the issue.

Sounds like a lack of circulation if the matrix remains cold.
Not a crappy plastic impeller on the pump like the vws use is it?

to check the water pump you should be able to run the cooling system in and out of a bucket,... I did the same on my Zetec,. just to check the direction of flow,...

maybe an option,..

It looks like a sealed external unit so without stripping it to pieces i don't think i will know if the impeller is plastic.

MINI COOPER AND COOPER S WATER PUMP FROM 2001 ONWARDS MEYLE GERMANY NO 1 HD

The front of the car is stripped ie all the body work after replacing the radiator, so getting the water pump off for a look is probably the next lo cost option.

check the stat is opening before getting too involved ?

Conrod - already done. replaced as it was a cheap item.

vasser pompen then

Water pump impellers break up or spin on the shaft ,if left overheats too many times and head gasket blows. I hate minis totally overated cars.

what were the white bits in the rad? bits of chewed up water pump impellor by any chance?

Just run the pump in and out of a bucket as mentioned above. You have the ideal situation with an external pump! You will be safe without cooling for a minute or two.

[Edited on 14/5/14 by coyoteboy]

Pete - you make a good point but i don't think so, it looks more like flakes of limescale.

Getting to the pump is a little bit more involved than i thought but that will be the next option to try.

Well, finally got some resolution on this. It was not the radiator, stat, airlock, headgasket or water pump.

The gears on the Eaton supercharger that drive the water pump had ceased to exist.

Next stop... New supercharger