Radiator cap poundage

[Limey57]

My radiator cap is marked as being 13lbs, but I'm finding that it's pushing some water out, is 13lbs correct or should I be using something higher?  Engine is a 302 Windsor, stock radiator.

Thanks

[lalessi1]

I would think that is more than sufficient. I am thinking maybe thermal expansion is the culprit and it will stop at some level. Steam would not overpressure the system until the temp reaches 245 degrees F.

[RICH MUISE]

Gary, somebody will have to confirm this, but I recall a stock radiator as having a suggested cap pressure of 7 lbs to keep higher pressures from rupturing the tank. With that said, I ran a 7 lb on my new aluminum radiator, but found that it was spitting coolant over the top of the engine, so I switched to a 13 lb and have had no issues since. My aluminum radiator is welded though, not brazed as the oems are.

[Marc]

Whenever I ran a 13 lb cap on my stock radiator, it was always springing a leak at the top tank. Dropped it to a 7 lb cap, fine ever since.

[hiball3985]

Sometime over the years the depth of the neck changed, I don't have access to my original radiator to check it's up in the rafters. I remember trying a later higher pressure cap on some early radiator and it didn't seal. I could fill the radiator and squeeze the radiator hose and it would spit out the overflow because it didn't seal..