Abstract: A device and method are disclosed for simultaneously testing the fluid tightness of the entire pressurizable coolant system of an engine, such as an internal combustion engine, including the radiator, the coolant flow passages within the engine block, the pressure-type radiator filler cap and the connecting hoses. The device and method of the invention further provide for simultaneous testing of the integrity of the outer and inner seals typically formed by the pressure-type radiator filler cap with the radiator filler neck.