4-7 psi cap for Griffin radiator?

[36fordguy]

You are missing the problem with Griffen radiators. The radiator itself requires about 11 lbs pressure (dynamic ) to fforce the water thru the radiator. A external cat (top of radiator) has to be more than this or you will pump water out the over flow. If you less than this on the top cap you water pumps suck on the bottom of the radiator reducing the pressure (dynamic) on the water going into your pumps aloowint the water boil (vaporize) - So the whole system has to be closed loop at about 15 lbs to work correctly like modern cars and radiator system chang the top cap is not the thing to do. Old rad's thhe water flowed thru the rad by gravity. The pumps only got the water to the top of the radiator.I changed to a brassworks rad. that requires less dynamic pressure to the water flow thru the radiator. The you can reduce the top external pressure of the cap. 36fordguy