Checking pressure drop in cooling system:
WARNING: This page is about a different car, the 2002 BMW Z3 and 2001 BMW Z3. However, it is still accessible from the selected car via links, so may be relevant.
Remove cap on expansion tank. Attach special tool 17 0 002 /17 0 005.
Build up gauge pressure of 1.5 bar, wait approx. 2 minutes.
Courtesy of BMW OF NORTH AMERICA, INC.
Cooling system is impervious to leaks if pressure drop is max. 0.1 bar.