56 chevy help???
 

hey, i'm working on a 56 chevy 1 ton, and i have a question on the radiator cap. first off the truck now has a baby 400/th400 combo and a stock 3/4 ton radiator in it. the radiator i just got used and had it boiled and cleaned and good to go. the radiator had an original gm ac cap that was marked for 5 or 8Lb. but the original radiator that was with the 400 was a 16Lb. which radiator cap should be used? there is no heater in it right now but i have one to put in from a 3/4 ton. thanks

Re: 56 chevy help???
 

I just rebuilt my radiator and put a copper 4-core in the existing frame for a SBC 350. The old timer radiator quy said to stick with a 6-9lb cap so that it would not build up too much pressure and blow the welds. He said that I dont need any more than that. It runs fine and cool.

Re: 56 chevy help???
 

I might be wrong but i think the higher poundage caps are used on a closed system radiator set up, with a overflow reservoir the lower poundage caps were used on older vehicles that just had the overflow tube mounted on the rad and vented to the ground Correct me if Im wrong :canada:

Re: 56 chevy help???
 

ok, thanks for your help.

Re: 56 chevy help???
 

The higher the pressure, the higher the temp when the coolant boils. If you're going to run the lower pressure cap you might want to use a 180 T-stat to provide a wider temp range between operating temp and boiling temp. Radiator guy might have seen something he didn't like or just might be playing it safe. Can't tell without talking to him. But next higher cap pressure is 10-12 psi and that's what I'd use with 195 T-stat.

The difference for the recovery bottle (overflow) type system vs open system is a small gasket on the bottom of the cap. Look at the original cap upside down and it's probably just brass on the bottom with a gasket inside the cap. Look at a newer cap and there's a gasket where the brass is on the old one. You can use the recovery type cap on the non-recovery system but not vice versa. If you run non-recovery bottle don't fill the radiator to the top or it will push out coolant when it warms up.