WARNING: This page is about a different car, the 2003 BMW Z8, 2002 BMW Z8, 2001 BMW Z8, and 2000 BMW Z8. However, it is still accessible from the selected car via links, so may be relevant.
RADIATOR AND MOUNTING PARTS E52 / S62 SPECIFICATIONS
Cap for cooling system
Pressure relief valve opens at overpressure to ambient pressure
bar
2 +0.2-0.1
Vacuum valve must open at latest at partial vacuum to ambient pressure