It does happen to many vehicles. Mine does it since I replaced the upper rad hose with a Rein and have tried three different/new radiator caps. I have seen the problem in many different vehicles and even stocked a rad cap that didn't have a vent valve spring for that reason. The problem then becomes the vent valve possibly not closing and there are advantages to having the slight vacuum after cool down.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)