Radiator Pressure - What am I missing?
 

I'm probably gonna' feel real stupid when this is answered but I'm working on an Old Nova with a 194 6-cylinder. It's overheating after about 5 minutes.

The water pump is new and it had recent head/valve work whereas the head checked fine.

I bought a new cap and thermostat and all the sudden I'm sitting here thinking:

The radiator building pressure is what raises the boiling point for the coolant. The system pressure on this car I think is rated at 13PSI (could be just the cap???).

At the top of the neck is an overflow tube. How the heck can this system build pressure with a hole in the side of the neck? It doesn't seem that this would be a "sealed" system.

Mike, even our cars have this hole in the neck, this is what goes to the overflow tank. The radiator can build pressure because it seals at the lower portion of the cap. You know, the part with the small rubber seal connected to the spring. That actually presses down on the radiator neck at the bottom, and seals. The gasket around the top of the cap, seals the final bit, allowing coolant that gets pushed past the first seal (around max cap pressure) to flow into the overflow tank.

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Rob
'86 TA 305 TPI
Gutted MAF, Ported Plenum
TB Bypass, Home made Cold Air Intake,
Edelbrock T.E.S.

Thanks Rob,

I was doing too much pondering and not enough looking. As soon as I put a new radiator cap on it I noticed how it sealed.