Abstract: The coolant changer machine is a device for transferring radiator coolant fluids, including new, used, and detergent fluids, between storage tanks and an internal combustion engine cooling system. When a vacuum is applied at the radiator cap, fluid is returned to the storage tank, and if the cooling system is hot enough, the fluid will boil can be removed. When air pressure is applied to the top of the storage tank, fluid will flow out of the tank, through the control system and into the engine cooling system. The control system allows for filling the radiator at the cap opening or through the thermostat. The control also allows for circulation through the engine cooling system when the engine thermostat is open to allow complete mixing of flush detergent at elevated temperatures to thereby improve flush performance.