I have a 1972 Cutlass Supreme U code 455. I noticed it was starting to get in the 225 degree range and higher when driving. So I installed new aluminum four core radiator and new clutch fan. Then the water pump went installed new water pump and 190 degree T/Stat. The ATI radiator has a 19lb cap. My car no longer gets hot, but the upper radiator hose and bottom hose hold pressure when cooled down? If I remove rad cap it over flows when cooled down from the pressure. Would the rad cap cause this if it was bad or possible air pocket? Not sure what to think of this? Any help would be appreciated. Thanks Jim..

 

The purpose of a sealed pressurized coolant system is to RAISE the B.P. (Boiling Point) of the liquid coolant. The boiling point goes up 3° F for every pound of pressure (psi). Albeit, a 15-psi radiator cap will raise the boiling point by 45° F. A 19 psi radiator cap increases the B.P. by 57° F. Since the B.P. of liquid water is 212° F (with no antifreeze), the effective B.P. of a sealed coolant system w/ a 19 psi radiator cap = 269° F.

Yes, both the upper & lower radiator hoses will maintain pressure for an extended period of time. When you say "cooled down", you should provide data e.g. a known temperature measured with a known working & calibrated temperature probe really to understand what's going on here. When you removed the radiator cap, you effectively REDUCED the B.P. The sealed coolant system is no longer under pressure & coolant will readily puke (overflow).

 

Next day hoses are hard from pressure when checked.. It was not like that before..

 

Did someone recommend a 19 psi radiator cap?

 

FWIW, hardness of a hose is simply an indication the cooling system is under pressure. So, the perceived "issue" here is the coolant system is operating as intended (no longer gets hot I guess), no leaks, etc. but the radiator hoses hold pressure? I'm not sure there's an issue here. If I turn off the water to my garden hose at the on/off spigot but do not open the end of the hose to relieve the pressure, the hose will remain hard. Still not sure there's an issue.

 

That's what came with new radiator. Seemed kind of high to me but that is what they sent? I was thinking of going down to 15 cap.

 

IMO, a 15 psi cap would be preferable.

 

I would think after radiator cools down and reaches atmospheric pressure the hoses would not be hard and full of pressure? Thanks for the advice..

 

Are you leaving some head space in the radiator for the fluid to expand?

 

Your 1972 originally came with a coolant recovery tank, and you should have the proper radiator cap installed along with the recovery tank. When the coolant gets hot, it expands into the recovery tank, and as it cools, it is drawn back into the engine coolant system.