TOPIC:

A tight radiator cap is a must for this siphon to hold Also no pin holes, cracks or leaks in the tube connecting the radiator and overflow tank.

If there is a leak in the engine, gasket, pipe, or crack in the metal, this too will cause a loss of coolant to flow back and forth into the overflow tank, once it empties from any possible leak.

T.

So you're saying that the radiator cap holds the cooling system at the rated pressure. Vents excess coolant to the over flow and then allows the coolant to back flow if the volume of the coolant diminishes when it cools down? I suppose I know the answer, that's why over flow tanks exist. Still I'll have to take a closer look at my radiator cap to find the second sealing surface.

Thanks

Bill