Radiator Cap PSI

[Minkota]

Currently my system has a 7PSI Cap installed but it will start spitting water after it is shut down. what PSI is recommended for a 383 small block with 50/50 mix and Vintage Air.

[Stocker]

Stock is 15 - 16#. I don't see any reason your 383 would be any different. If you don't already have an overflow tank, it's a cheap, easy, effective upgrade. You'll need a cap for a sealed system (if you have a tank).

[Minkota]

Originally Posted by Stocker

Stock is 15 - 16#. I don't see any reason your 383 would be any different. If you don't already have an overflow tank, it's a cheap, easy, effective upgrade. You'll need a cap for a sealed system (if you have a tank).

I was more concerned with the Vintage Air being installed than the 383. truck does not have an overflow tank.

[54blackhornet]

7lb is to low to raise boiling point much.

[sick472]

All the older (pre-72) vehicles that I have had the pleasure of owning would puke coolant after shut-down...IF it was filled all the way to the top. Try this, let it do it's puking a time or two (if it even needs to puke twice), let it cool, look into the radiator and do not fill it over that mental mark. Typically, I find that the appropriate level lands at the top of the fins.

I'm not saying that the 7psi cap is appropriate as all of my older cars have that 15-16# cap. Changing it to a 15-16 cap will increase the boiling temp of 50/50 coolant by about 22 degrees F. This helps IF you car tends to run close to 268 degrees F and is actually boiling the coolant....BUT, it your not running that hot and not boiling your coolant...the coolant will still expand at the same rate when it gets hot regardless of the cap pressure rating (within reason). I would bet you are not boiling your coolant, just heating to up. This causes fluid expansion and you just don't have anywhere for it to expand. Leave some room in the radiator for it to expand or add an expansion tank.

[MJN]

Originally Posted by Minkota

I was more concerned with the Vintage Air being installed than the 383. truck does not have an overflow tank.

What your concern with the Vintage Air? The A/C isn't tied into the cooling system other than having the condenser out in front of the radiator and as with any stacked cooler design transfers heat from itself to the radiator. Do you have a fan shroud or any overheating issues?
I agree with the others, get a 15/16 lb cap and leave room in the radiator for coolant expansion when it is hot.

[Stocker]

Agree with the above -- 7 psi is the wrong cap, and your A/C has nothing to do with that. Leave your coolant level low or add a tank so you can fill the radiator.

[Minkota]

Originally Posted by sick472

Try this, let it do it's puking a time or two (if it even needs to puke twice), let it cool, look into the radiator and do not fill it over that mental mark. Typically, I find that the appropriate level lands at the top of the fins.

I tried that and it doesnt stop puking until the radiator is down 1-1/2 gallons.

Originally Posted by MJN

What your concern with the Vintage Air? The A/C isn't tied into the cooling system other than having the condenser out in front of the radiator and as with any stacked cooler design transfers heat from itself to the radiator. Do you have a fan shroud or any overheating issues?
I agree with the others, get a 15/16 lb cap and leave room in the radiator for coolant expansion when it is hot.

My only concern with the AC was that it may possibly be putting slightly more load on the motor, causing a slight increase in temp.

Originally Posted by Stocker

Agree with the above -- 7 psi is the wrong cap, and your A/C has nothing to do with that. Leave your coolant level low or add a tank so you can fill the radiator.

I know some people use 7psi to avoid premature wear on radiator and heater core, but thats not really a concern of mine. I have always run at minimum a 13psi but wasn't sure what the recommended psi was.

[Stocker]

Originally Posted by Minkota

I tried that and it doesnt stop puking until the radiator is down 1-1/2 gallons.

Well, that sure doesn't seem normal -- that is a lot of coolant to lose.

At the very least, I would suggest a sealed system with a recovery tank. If you're not overheating, that may be all you need. More than that, though, how's the rest of the cooling system? Radiator, hoses, water pump all in good condition? Fan shroud the correct size & shape, and the fan sitting ~ halfway into the shroud? Heavy Duty fan clutch with a six - seven blade fan? Just some of the basics to consider for an effective cooling system.