WARNING: This page is about a different car, the 2003 BMW X5, 2002 BMW X5, and 2001 BMW X5. However, it is still accessible from the selected car via links, so may be relevant.
RADIATOR AND MOUNTING PARTS SPECIFICATIONS
Cooling system cap
Pressure relief valve opens at overpressure to ambient pressure
bar
2+0.1-0.2
Vacuum valve must open at latest at partial vacuum to ambient pressure