With the engine running and the system full of coolant, and the radiator cap off, I can detect no movement in the water flow. I spit into the filler neck and the spit bubbles just stay where they are.

Yet when the upper radiator hose is removed water comes spewing out of it from the force of the water pump. And I know that the radiator isn't stopped up because when I do that it drains as it's being drawn into the engine via the pump.

Why can't I see movements when I look into the radiator?

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)