When someone would come in and we would find the upper hose collapsing, or trying to, the head of the shop would first replace the radiator cap, as another response said. If that did not solve the problem, then he looked for a restriction, usually a plugged radiator. I remember one time, I pulled the radiator on a 1966 Mustang, (radiator looked great) and found that the coolant had turned to "jello" in the bottom tank. Only saw that a couple times in cars that sat around alot. Something is restricting flow, Barry might be right about running the bypass.