Inliners International Forums General Discussion Engines radiator cap

Here is what I'm working with.

1948 chevy fleetline
stock radiator with 3core
1958 Chevy 235

I started off using a zero lb radiator cap. Water was leaking out of the overflow. I switched to a 4lb cap, now water leaks out occassionaly through the the overflow tube. What is the highest pound cap I can use without damaging the raditor or blowing a head gasket? Would a 13lb cap be safe?

I live in Sacramento, Ca. so it's usually warm weather.

A 1948 Chevrolet Fleetline has what is called an "open" cooling system. On an open system, the overflow exits out at the top of the tank. On the more modern radiators, it exits on the neck and, consequently, the cap holds the pressure of the radiator at the flange just below the spot where the overflow exits. When the pressure exceeds the amount of pressure the radiator is designed for and the cap will allow, the cap will release and the pressure and overflow will be allowed to exit the system by pushing on the pressure cap. On an open system, none of this is applicable. The system is designed basically for no pressure at all and any type of cap will have the same results since the overflow exits from the top of the tank and there is not a flange on the neck of the radiator. The only way to control the overflow on a stock 48 Chevrolet Fleetline is to run an overflow tank and the small amount of pressure which causes some small amount of overflow will, as it does on a "closed" system, draw the water back into the radiator as it cools. In most cases this will allow you keep your system full of coolant and function correctly.

Joe

thank you for your quick response, but I do not think that is correct for 1948. My radiator has a flange, and the overflow is on the neck. The book calls for a 4lb cap, but the raditor cap for a 1958 chevy is an 8lb cap. So I trying to determine if I put a higher rated cap on this radiator if it will cause any damage.

I think 1941 is the last year of a zero pressure radiator. (but as usual, I could be wrong, that's why I'm posting the question)

I have run a 7 lbs cap on my 47-54 truck radiator for over a decade daily. Also with a late 235.

I believe the pressure limit has more to do with how much the radiator core can handle.

A few years ago I recored the radiator with a 3 core.

Higher coolant pressure increases the boiling point.

A higher pressure cap may cause more leaks on an old radiator core than a lower pressure cap and the hoses may need replacing sooner as well.

Dear Modiol;

You may do it either way, with or without the pressure cap. If you run W/O pressure the fluid will seek It's own level in the top tank and not drop any further. This will be about 'half full' which is just fine.

The system will hold what It's designed for (0-4#) and probaly 7 without any problems. If (that word again) everything else is in good condition etc.

Head gaskets "blow" for OTHER reasons.

Almost all 40 vehicles vehicles ran W/O pressure in the cooling system and if It's not overheating, all is well.

"Don't worry be happy".