Correct PSI for rad cap and overflow

-
Valiant273

Valiant273

Active Member
Joined
Jun 29, 2016
Messages
25
Reaction score
6
Location
Ottawa, Ontario, Canada
Hi Guys,

Just wondering if I'm running correct rad cap with 7 PSI? Seems low.
Also should I consider adding an overflow bag/container.

If my temp gauge is correct I run at about 165 when in light traffic and about 190 in heavy stop and go traffic. This is lately with the 30C ish temps.
Do not know what stat is in it.
 
And this is what car,what engine,& have you maintained the current setup?
 
Ah yes I figured I let out some pertinent info :)

1965 Valiant with 273. Comp cam, edlebrock intake, 4 BBl Edlebrock carb, Spitfire headers, full dual exhaust
 
My rule is the lowest pressure that will keep it from "puking". If the system (rad, hoses) is in good shape there is no reason the system cannot stand the highest press available, the more pressure DOES put more strain on everything.......hoses........heater / rad core, core plugs, and pump seal.

The weather you will find yourself in, and high altitude makes some differnce.
 
I had a radiator man that has been in the business 50 years tell me to run the 7 lb cap in these old cars. I have run both 7 and 14 for years. if everything is in goo d condition, I have no trouble with either cap.
 
Originally the 7 lb caps were favored for high altitude areas, I almost never saw them in junkyards in the flatlands.
 
Every # of pressure will raise the boiling point 3°. If you are having boil over issues and like mentioned your system and hoses are in good shape, you can put a higher pressure cap on. If your engine just heats up to 190° in traffic and doesn't blow coolant out the overflow, you don't have a real issue and you should be good to go.
 
7 pounds is definitely not correct or beneficial unless the one and only goal is to squeeze a few more miles out of a whupped cooling system or other fault until you can fix it correctly. Read this 5-part article (one chapter deals specifically with cap pressures and such).
 
Darthomas said:
Originally the 7 lb caps were favored for high altitude areas, I almost never saw them in junkyards in the flatlands.
Click to expand...

Why would a 7lb be better at high altitude? If anything a HIGHER pressure cap would be better
 
67Dart273 said:
Why would a 7lb be better at high altitude? If anything a HIGHER pressure cap would be better
Click to expand...

Remember the cap rating has nothing to do with external pressure, it's rated for the internal pressure and it's strictly mechanical. It's 7lbs at sea level or 6000ft, the water in the radiator will boil at the same temp. But the outside pressure is lower, so, there's more stress on the hoses and radiator because of the larger pressure differential with the atmosphere. So, lower cap pressure at high altitudes.
 
My 1975 Stant Catalog and the 65 S.M. show a 14 lb. cap with a 180* t'stat. If it's holding at or below 190* on hot days or heavy driving as you put it, you are in fine shape. For the really hot ones, or pulling a grade, you'll need the spec'd cap.
 
Last edited:
You must log in or register to reply here.
-

Back
Top