454cid
Sooper Pooper
The radiator is in communication with the block via the bottom hose so the pump sees an open path (assuming a clear radiator - which appears to be the case).
True, I didn't think of the lower hose.... outa site sotta mind, I guess.
As mentioned earlier, pressure is from heat - or gasses escaping the engine.
I understand, but I'm talking about a cold engine.