Packard Forum Index » Pre-War (1899-1942)

The 1939 systems were non-pressurized with the radiator having very large cans that cannot tale any pressure, They might get by with a 4lb cap but no more than that! I once tried a higher pressure one and watched the tanks grow before quickly taking the cap off before any serious damage happened.

Most of the unpressurised radiators have the overflow tube below the level of the cap seal seat. So chainging the radiator cap won't many any difference, unless you sealed off the overflow tube.

Don't seal off the overflow tube!
The cap should have a gasket to prevent water loss at that point. The overflow tube inlet is located near the top of the tank to maintain water level.

With the car sitting level and the engine off and cool, it should be possible to fill the radiator completely full to the level of the cap. At that point some water should run out the overflow tube until the water level is about 1/2 to 3/4 inch below the filler neck.

Refer to the Literature archive 1939-'39 shop manual for cooling system info.

After some discussion with my friend Terry Weiss, a long time Packard mechanic that lives near me, I recalled that I had removed my engine thermostat last year for some reason. We believe that the motor needs that thermostat to help slow down the water flow going up to the radiator. I can't find it so I ordered all new pieces from Maxx Merritt and will install them and find out, fingers crossed.

Read the shop manual. (Ignore the part about alcohol antifreeze)

I wanted to give an update, I installed the new block thermostat on the head and filled it with water for a test, now, no water is blowing out of the radiator. At a fast idle there is no bubbling which I take as a good sign. I ran the motor for probably 15 min. at various speeds and the temp stayed right around 180. I didn't have the cap on and once when I revved it up pretty high just a little water came out of the radiator but I think it was overfilled. I couldn't go really drive the car because I had some other parts off but I am very encouraged.