Alright I borrowed a coolant pressure tester from auto zone hooked it up with 21 lbs on it no signs of any leaks. Over 15 minutes it lost 2 lbs somewhere. So now what increase pressure the max on this pump is 30 lbs but I'm not into going higher than 21?? Thoughts??

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92 e300d2.5t
01 e320
05 cdi
85 chev c10