The Stovebolt Site Forums The Shop Area The HiPo Shop radiator cap

I just got my '49 going with a fresh 350 motor and will have to use the original radiator yet for awhile . Its been rodded out and worked fine on the 6cyl. Now it seems to be just on the edge of not doing the job on 90 degree+ days and I don't know what the old radiator cap is holding so How much of a preasure cap will the old one hold without busting the seams ? I know that I will need to upgrade someday to a new radiator but that wont happen soon.

I talked to the radiator shop just the other day and he recommended staying with a low pressure cap 7-9 lbs He said old radiators couldn't handle much more than that.

I'll 2nd the rad shop, never use more than a 7# cap on pre-60s rads - I believe 49 originally spec'd less, maybe 4#

Bill

Need to ad an electric fan, did the trick on my '46.

OOOK guys, correct me if I'm wrong but on the original I thought they did not run a pressurized cap... but I guess it did hold "some pressure".. I'd say no more than 4lb???

On another note and just as a comment......
When I put the 350 in my 37 I had the original radiator rebuilt with a NEW core. BUT I also had the neck cut out and another one put in where I could run a good pressure cap. BUT I also used the ORIGINAL top and bottom tank... Therefore I was afraid to put much pressure on it as the brass tank was thin and I knew it would rip if to much pressure. So, I ran a 7lb. It would spit a little out the overflow but never really had problems unless in a parade or something.
Well, after several years it started leaking right from the tank seal right under the top neck...... Radiator shop wanted so much to redo it I bought a universal Griffin Radiator for half the money and now the problems are gone!
Moral of this long story.... do it once and do it right Like I should have done in the beginning.

chip - the no-pressure was deco and earlier, I think by the 47 AD it was 4#, the TF series is 7#, not sure when that started, maybe 54?

Bill

The 350s tend to run on the hot side.200 to 210 is not unusual,for a 350.Another thing not mentioned here,is what thermostat are you using?

Thanks guys , I do have an electric fan mounted on a full shroud sealed to the back side of the radiator and am running a 160 full flow thermostat. It seems to do ok if I let it purge out and don't top off the radiator again . It's just hard for me to get over the "Top Off the Fluids" thinking and fill it up again . Also , if I put an overflow catch can on the radiator will that require a different cap inorder to let the coolant back in to the radiator ?

Hope you get an answer for this one, I added an overflow (old coke bottle) and replaced the rad cap (from LMC Truck) on my truck. I haven't had a chance to drive the truck since I put it on. If I get her on the road anytime soon. I'll let you know. Never did think about there being different types of rad. caps.

No your existing cap will work with a catch tank, pressurised radiator caps have to let air bleed back in through the overflow and past the rubber seal when the motor cools, otherwise the radiator hoses woud collapse as the coolant shrinks. If you fit a catch tank the radiator just sucks in coolant instead of air.

Stuart.

actually, there are two types of radiator caps. A double seal cap is required for an over-flow catch tank. Non-catch tank setups only need a single seal cap.

Interesting, perhaps there's a difference between European and US radiator caps then. All the ones I've seen here have a primary seal which maintains the pressure in the rad and a secondary rubber seal in the top of the cap that ensures venting occurs via the overflow pipe only; otherwise you'd be at severe risk of being scalded by escaping steam when the motor boils and the primary seal vents.

Stuart.