[G.M.]

4 lbs is good but the BIG PROBLEM is MOST caps don't seat down on the brass seal washer down at the bottom of the neck. If you line up the cap locks at the top when you push the cap down you can fell the spring tension of the rubber end of the cap hitting the brass seat down in the neck before the upper part of the cap hits. If it don't hit and seat you don't have a pressure cap. I have had to put a red rubber washer down on the seat so the cap seals on it on almost all the old Fords I have. G.M.