[charleshwy]

My car is 2012 118i M Sport. I have been experiencing the 'Low coolant level' warning in the last few months. I refilled the coolant, and the warning popped up again in about 1 month. But I can still see coolant in the expansion tank. My monthly mileage is around 1200-1500 km.

Any idea what might have gone wrong?

[stupar]

There are a lot of threads regarding coolant leaks on this forum. I've had several coolant leaks on my car.

First of them was the O-ring on the coolant temperature sensor, so I have bought the new sensor along with the O-ring, replaced it and solved the problem. You can check this video out for more info:

The second one was the cooling system pipes, actually it was a profile gasket and an O-ring on the part that failed. It was a pain to replace it, put it can be done. This is the part list you will need (numbers 1-7 on the picture; no. 5 is the sensor I mentioned above).

http://bmwfans.info/parts-catalog/F3...ng_system_pipe

The third one for me was the cooling (expansion) tank cap which failed, easy and cheap to replace.

Many people had bad luck with the expansion tank itself, since its the plastic part and plastic is prone to crack. The most important thing is to find where the coolant is leaking so you can sort it out with the replacement part. Its easy to find the leak spots since it leaves white and/or green marks all over the place. Should be an easy fix.

[charleshwy]

thanks a lot for the information!