The Stovebolt Site Forums The Shop Area General Truck Talk radiator cap

I'm helping a friend with a 47 1/2 ton that has a later 235 engine in it. Originally this was a non-pressurized cooling system. Can he still run a non-pressurized radiator cap with the newer engine or does it need to be a pressure cap? The problem he's having is the heater core can't handle any pressure. It keeps developing leaks with a 5 lb. cap on it. Dave

1. replace the heater core, problem solved
2. get a 2 lb cap and container of alumaseal or copperseal if you can find it. Dump it in , change the cap and start looking for a new heater core,
3. find a non pressure cap or just leave this cap loose, on the first stop. drive it until the weather heats up enough to boil over. (unless he has a super clean cooling system)
Then replace the heater core.

4. bi-pass the heater core

That's what I did, course we don't need no stinkin heaters here in So Cal, just put on a sweater in the AM.....If it's that cold, just drive the Durango.

Unable to find this style heater core. So a 2# minimum cap would be recommended along with some stop leak? Dave

5. remove heater core, bring to radiator shop for re-braze/repair, reinstall. i would never put stop leak in any vehicle I cared about. Next month you'll be posting about the engine overheating...

Yep, finding those heater cores can be difficult. The radiator shop could not repair the one out of my 54' 3600 and I finally found a good one on ebay. Here is an option you may want to look at........
http://www.thebrassworks.net/shop/H...irculating-Heater-Core/product_info.html

cold = bad
heat = good

good luck

It's been at the radiator shop and they wouldn't try to repair it so I soldered up the leaks myself. Just thought I could try stop leak if it sprung anymore leaks. This is a rectangular core about 6" x 7". Not the more popular round one or long rectangular style. Thanks for the replies. Dave

The only reason to run a pressure cap is to raise the boiling point of the coolant. Every 1 PSI of pressure raises the boiling point 3 degrees, so unless the coolant is getting above 212 degrees for some reason no pressure should be needed. Just install an overflow tank and don't fill the radiator all the way to the top. Any coolant that ends up in the puke tank will get drawn back into the radiator, as long as there's a good seal between the zero-pressure cap and the top of the radiator filler neck. You can make a zero-pressure cap by removing the lower rubber gasket of the existing cap.
Jerry

My son has a 1946 2 ton with original 235.
Replaced old cap with a new non pressure cap
and he had no problems.

The fall of 2016 a rebuilt 1954 235 was install
and still using the non pressure cap and still
no problems. Jeffrey

Can you find another radiator shop close by??? We have an older shop here that will actually order the pieces it takes to "make up" a heater core but I'll admit, its a bit pricey at around 200 bucks but then most of us would never have to worry about it in our live time....or at least it could be repaired later.
Don't give up just yet...........

Stant 10203 is a 0 pressure cap. Napa can cross reference it to their brand. Amazon also has Stant 10203.

So it is ok to run a 0 psi cap. Thanks for all the replies. Dave

Yes, a 0 psi radiator cap is OK.

4psi should also be OK.

If you go higher, you might be moving into pressure-territory that might be too high for other components (the heater, for example).

Hey Jerry,
For an overflow tank to function, doesn't the radiator cap need to have a tight seal as the antifreeze cools off? The coolant loses volume as it cools, creating a vacuum which is the force that draws the coolant back out of the overflow tank. If the cap has had the seal removed, wouldn't that break the vacuum, preventing the coolant to be drawn back into the radiator? Maybe I don't understand how a pressure cap, modified by removing the lower seal works.
Carl

As long as the neck of the radiator is sealed then all the pressure/vacuum is acting on the overflow tube. A pressure cap with the lower seal removed still seals the top of the neck.
You should always start with the radiator full to the top and the tank 1/2 full. It will eventually equalize to a level doesn't overflow and is air free.

Jim's got the picture. There is a flexible metal piece at the top of the cap that seals the top of the filler neck as the cap is tightened fully. It would also be possible to drill the top of the radiator cap for a long sheet metal screw that would retract the spring loaded center of the cap slightly to prevent pressure buildup. A factory 0-PSI cap is a better choice, though.
Jerry

Thank you for the education gents. (Glad I didn't go all "I-told-you-so, what-were-you-thinking-with-your-2-3-braincells-to-rub-together, etc. )

I learned something there too!