I believe the Bentleys manual says you should pressurize your system to 21.8 psi and it should be held for 2 minutes. It should not lose more than 10 percent (if my memory serves)of its pressure in that time frame in those 2 minutes. I think mine dropped from 21.8 to 21.5. My two cents worth. I will check my manual after I get off work.

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2000 BMW X5 4.4i Sport