13 should be fine if your hoses and any other utilities such as heater core are up to task. Maybe 7 psi was 59 spec? 13 -15 is more standard on later models and 7 allows no boilover protection as you've found out.

By reaching operating temp you "MIGHT" also be exposing an internal engine problem allowing it to pressurize the cooling system. Don't overlook that. If you overheated it before the repairs there's a chance something got tweaked.

 

Another thing to consider; Many of the older style radiator caps were taller and reached down deeper into the radiator neck. If you have a modern shallow cap on a deep neck radiator, the lower cap seal may not be sealing in the neck at all and may be allowing the expanding coolant to pass directly through to the overflow tube instead of building pressure as it should.

As far as the cap pressure goes, personally I wouldn't second guess the radiator shop. A radiator explosion could send you to the hospital or worse. Better safe than sorry, IMO.

Hope this helps..... :thumbup:

 

the 12psi cap is just as deep as the 7psi cap so I think the depth of the 7psi cap isint an issue but I could be wrong. Just to test it out I put the 13psi cap back on and it wasnt letting any pump out at operating temp.

 

If there is no coolant recovery bottle,you are only supposed to fill coolant to top of the core to leave room for expansion

 

no recovery bottle but I am thinking of adding one in the near future. 195 degree tstat and remember its a 1980 454 motor so this thing runs hotter than the stock 6/8 cylinder motors from the 50s.

 

GM radiator cap pressure

GM specified a 7 lb. radiator cap on the low pressure radiators through 1958. In 1959 GM introduced high pressure radiators which used a 13-15 lb. cap. Therefore a 13 lb. cap is what you should be using.

 

if gm had a 13lb cap from the factory why would all the auto parts stores like pepboys, autozone, and kragen show a 7lb cap as OEM for a 1959 chevy truck with a factory 283 v8?

 

I would go back to the higher cap and install a recovery tank.
When the system cools back down it doesn't have any coolant to draw back into the system so it pulls in air. Do that enough and you will end up over heating for real.

 

Passenger cars

Sorry, my error.

Chevrolet pick ups used a 7 lb. cap until 1962. Only the 1959 and later
passenger cars use a 13 - 15 lb. cap and GM pick ups started using a high pressure radiator in 1963.

 

hey just wanted to give an update. I ran the 13lb cap again and let the coolant run out of the overflow tube until it wouldnt anymore, stopped after the level in the radiator reached a certain point (it was still basically full) and stayed that way so I think like it was posted above that there wasnt enough room for the expansion. After I figured out the system was OK I installed an overflow tank and seems to be good now. Thanks for the help again guys...still cant figure out why that 7lb cap would open up at operating temp though

 

What temp Thermostat did GM use with that 7-lb. Cap?

 

The boiling point of water is raised by pressure. At sea level, water boils at 212*F at atmospheric pressure. Add a 7 pound cap and it will boil at ~230*F, a 14 pound cap at ~250*F. That engine temp is controlled by your thermostat. If you have a 180 or a 192 degree 'stat, then that hot rush of water into the radiator will probably overcome a 7 pound cap, dumping the water as it hits the low pressure cap. Once it's open, out a bunch of water will go. A '59 Chevy probably ran a 160* 'stat with that 7 pound cap along with a much lower volume water pump. Now, hopefully, that radiator will withstand the added 6-8 pounds of pressure (probably will).

A comparison - think your ol' ma's pressure cooker

(The boiling point numbers are rough, within 4-5 degrees, but close enough for this thread discussion.)

Dave W

 

Hey everyone. Ive got a 59 chevy truck with a 1980 454 motor. Factory radiator that was recored to work with the v8. It had a leak so I took the radiator to the shop to be fixed. They got that all fixed up but said the 13lb cap I had on there was the wrong one and told me to get a 7lb cap. I did that and now when the truck reaches operating temp the cap opens and starts leaking out coolant.

Should I go back to the 13lb cap since that seemed to work or what should I do? Thanks,
-Steve

I'm with Jake_Dragon on this, if it doesn't have a coolant catch reservoir install one. Two purposes the first is just to keep coolant out of the environment.

The second is more important to the engine and cooling system. The enemy, besides using tap water, is air. Higher pressure systems operating at higher temperatures net more expansion of the coolant. When this is vented to the enviroment it's lost to the engine, when the engine cools a vacuum is formed and the cap opens a vent allowing whatever is at the end of the overflow tube into the radiator. When it's air this provides the oxygen to launch corrosion inside the cooling system. The catch tank is designed to trap the vented excess and with that and a reserve amount it keeps the vent hose submerged in coolant so that when the system cycles back to cool it draws coolant rather than air. This reduces the chemical reactions eating away at the parts of the cooling system keeping the system clean and effective for much longer time than was seen with the old systems.

Keep in mind you're not running a 59 engine, it's an 80 and cooling systems changed a lot over that period to improve cooling and system life span.

Bogie