AirborneSilva

What should the radiator cap pressure rating be? I don't know that my cap is opening up to allow fluid to flow into the overflow tank. I put Amsoil's brand of water wetter in the overflow tank, so if it was trading fluid with the radiator I should be able to tell by it changing color but it hasn't. So I'm guessing that maybe the pressure of the cap is too high? just looked at the cap, it's 16 lbs.

gcusmano74

16 psi is a typical radiator cap pressure setting for a Chevy smallblock.

AirborneSilva

Cool, thanks

BKarol

In 78 it calls for 15.

AirborneSilva

Thanks Karol.... I was wondering if I put in a a 13 psi if it would allow it to trade fluids with the overflow helping it to stay a little cooler. It isn't a problem now that the weather is damn cold here but in spring and summer it might help, or I could just be cazy which is likely the case I'm sure

mds3013

If you want to add something to the active part of the cooling system you should remove the radiator cap, drain or siphon out the amount required then pour in the new. The overflow tank will only see the normal expansion into the tank and normal contraction back into the radiator if you have a correct radiator cap in place. It takes many heat cycles to exchange overflow tank contents into the radiator. mike...

AirborneSilva

thanks Mike, yeah i should have put it directly into the radiator but was being lazy. I did put a new radiator cap on it when i put the crate motor in, which was over 1K miles ago so it has gone through several heat cycles but doesn't appear to have exchanged fluids once