? about radiator (truck not Chevelle )

[chevymaher]

If the hose collapsed after it cooled down. It is a bad even tho it is new radiator cap.Or the hose to the overflow tank is blocked/collapsing.
When running it pushes fluid into the radiator overflow when it is hot and fluid expands. When it cools it should draw the liquid back into the radiator from the overflow.

So check to see if the overflow tube is unobstructed, that area on the radiator to. If that checks out the cap isnt allowing reverse flow.
But at least you know your cooling system is tight as a drum and not leaking.