**cooling system issue**

[LuckyRabbit4]

So I have a 1966 C10 that I've been restoring for a little while. Winter hit and I had to stop but now I'm back at it.

I finally got the 4.1 250 back together after blowing a head gasket. I replaced all gaskets and seals along the way. Also got a new upgrade to an electric choke from the factory manual choke.

It turned over, let it idle some to see how it would run then turned it off. Today, I filled the antifreeze to in the radiator normal height, replaced some rubber hoses and fuel line that attach to the new carb. New PCV valve line as well.

The truck wouldn't turn over so I went to check that I didn't unhook something. The radiator was bubbling and overflowing down the overflow tube. I knew it would explode if I took the cap off.

What could make this truck cooling system build up so much pressure in the radiator? It never started (battery needs jumped again). Just turned the engine about 15 seconds but no attempt to start up. Also, I'm replacing the heater core in a few days when that part comes in.