Antifreeze leak

Check the coolant reservoir. When cold, the level should be a couple of inches below the bottom of the neck.

 

it is air more than likely... use the search feature as there is plenty of information about this issue on here.

 

Sounds like maybe the spring in the cap is weak or you have the wrong cap (pressure). It should open, sending coolant out of the overflow hose, around 0.9 bar and under normal circumstances your coolant system should not be reaching that high a pressure. The expansion of the coolant caused by heating should be contained in the air space of the recirculation tank (that's why you don't fill it all the way up).

 

+ 1 Cheap and easy to replace. On the sticky in the 308/328 section, someone posted the STANT equivalent (i.e. Autozone, checkers, etc).

+ 1 Always check the level. 2 inches + / -, if too full, it will leak even with the right cap.

Good luck.

James in Denver

 

+1 - The cap has gone weak. The specified cap is now a 1.1 bar. I've just put my 4th one on in 8 years. They really are useless & don't last.

Don't mess about, just replace the cap - if you drop too much coolant (say if you get stuck in a traffic jam) the motor will cook and that gets expensive.

I.