Just tested with my new tester-3 times-ALL BLUE ALL THE TIME. Did notice the lower radiator hose collapsed (as well as the upper) while i was testing. Could it possibly be that the lower hose collapses the first time the t-stat opens because of the pump suction, causing my problem, then once the system has built up pressure from the heat, the lower stays open because of the pressure, hence no overheating till the engine is completely cooled off?