how can i fix my bmw 328 1 sport coupe auto?

check the filler cap is correctly rate and working as this releases excess pressure.
other faults could be.
thermostat not opening at all or fully
fan not coming on when it should.
water pump problem.
worst senario is the head gasket as that means a cylinder head skim.
lastly you'd be better off putting this question also in the cars section you'll get more mechanics reading it. i'm not one just going on past experience with old bangers.

B
October 2010