Weird cooling system behaviour

Thanks guys. Will do as advised and let you know what happens.

As far as I can tell I have flow, in the radiator at least as the flow is visible with the cap off and engine running.

That's good to know.

Do you have a overflow bottle.... a small hose connected to the top of the radiator going to a "bottle"

This might be a good time to bring this up:

My does not have one... it just spits it on the ground. I know that this not allowed on the drag strips. I had a 68 Charger a while back that didn't have one either. I bought a overflow bottle from Summit racing and flipped the bottle upside down so that the hose would be on the bottom of the bottle. It worked really good and there was always some coolant in the bottle but never noticed if there was more or less. My thinking was it would serve like the modern day "catch canisters". If the radiator cap opened it would push the coolant into the bottle and then suck it back out if needed. Does this sound like right?