Boomer I have 9lb caps on my 12V71 with a top gasket for closed cooling system. Check with JT on their operating pressures. Also, does it look like anybody has worked on your closed cooling water pump. Started sipping some better vodka with a friend tonight and this just popped into my mind; two different impellers. Standard and H O. While the coolant is out, pop that cover off and see if you can find a part number on the impeller. Go back to the stuff I sent you.