VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Radiator question

So I got my 41 AK back on the road after waiting on Ulphstery for a few weeks. I also changed the temp guage and in the process I lost quite a bit of coolant. I topped it off and filled it almost to the top of the radiator. It started blowing coolant out of the overflow hose after warming up. The original radiator cap didn’t have a spring for pressure relief and was leaking so I bought a new cap at Autozone with 8 lbs of relief pressure rating. I still was losing coolant for a short time but seems to be holding now. So my question is: do you leave about two or three inches of space at the top of the radiator for expansion when filling with coolant? Is an 8 psi radiator cap the right relief or should I go back with a solid cap? My service manual didn’t really address these items.
Thanks.

I didn’t mention the specifics but my AK has a 1954 replacement 235ci engine and the original radiator that was recored about 12 years ago.

Hi Planepal

Is the recored radiator in your truck the original or original style radiator?
Does the overflow tube come out of a "bump" at the top of the top tank?
If so, a pressure cap isn't going to build any pressure anyway, so you'll be better off with the original style sealed cap.
I think 8 lbs would be too high for those old radiators anyway

As for fill level...
I want the radiator to be just completely full when the engine is at normal operating temperature.
So...
To start I filled mine to about an inch below the bottom of the filler neck.
Then it will push a little out as it comes up to normal temperature.
Then after the truck is completely cooled off again, remove the cap and observe where the level is at.
From then on just maintain the cold level at that observed level.

Works for me! 🙂
Hope that helps.

Thanks. I’ll check the radiator for the bump. 8 lbs was the lowest pressure available but I’ll probably go back to the sealed cap. Thanks for the info.

nOTE THAT A PRESSURE CAP WILL NOT WORK ON A 1947 OR PRIOR RADIAOR,