It had been a slight loss of coolant over time since I got the car which I hadn't been able to trace so I just put it down to that, filled it up and forgot about. A couple of short journeys later she was empty again.
There was a lot of coolant on the outside of the expansion tank so I assumed I had fallen victim to the well known cracked expansion tank issue. I ordered up a replacement expansion tank and fitted it.
However, when I filled it back up with coolant my original top and bottom hoses leaked, it seems the o-rings that seal them don't like to be disturbed. Unfortunately BMW don't sell them separately and you have to fork out for the full pipe. I am sure I could've found o-rings to fit, but I was in a rush as I was about to drive to France so I wanted a permanent reliable solution.
However, getting the pipes from BMW was harder than expected, the BMW diagrams are not 100% clear and the car differs quite a lot from the six cylinders. I needed to replace the top hose and the pipe which attaches to the middle of the expansion tank.
So, originally the technician ordered completely the wrong pipe. I had to take pictures to get him to believe me that it was the wrong part. So I will try and describe the problem as best I can just in case it helps someone else:
The problem is this parts diagram which I've taken from realoem.com (the dealer's was identical) ... According to this diagram the large pipe (no 4) that runs underneath the radiator from the thermostat/water pump attaches to the middle of the expansion tank:
I thought the pipe was incredibly expensive when I ordered it (even for BMW) because the pipe I actually wanted is this one (no 7):
No 7 runs from the middle of the expansion tank to the heater matrix and is quite short, and has one of BMW's plastic attachments at one end and a jubilee clip at the other...
However, the dealer looked at the first picture first and it took quite alot of too-ing and fro-ing to get the correct pipe.
The large pipe actually attached to the bottom of plastic bracket that holds the expansion tank to the radiator (no10):
This is a different set up to the six cylinders which don't have anything going into the bottom of that bracket. You can see in this picture that there is a connector for a pipe sticking out of the bracket, this is where that long bottom hose attaches...
Hopefully that makes sense and saves somebody some time with the dealer! Unfortunately, after all that, the car still had a serious cooling problem... check my next post to find out why.