Venting will most likely happen during a heat soak after shutting it off hot. It won't likely happen while the vehicle is operating, because you have airflow, coolant circulation, and so on.

It is unlikely to happen in this weather in any case.

You really open the cap to check the cooling system every weekend? I can't remember opening my hood on any car that often, since a 76 Ford 400 cid V8 that needed valve guides in the early 80s.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue