If you're using a stock radiator, you can only use a 4 lb cap. Otherwise you risk rupturing the tubes.

I use a 4 lb radiator cap on my system. Just make sure that it has the poppet valve that modern radiator caps have so that fluid can travel in both directions.

Last edited by Otto Skorzeny; 06/18/2026 11:15 AM.
1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)