Prestone AS145 Radiator Sealer Stop Leak - 11 oz. Patented formula quickly stops leaks in radiators, water pumps, and heater cores Boosts corrosion inhibitors to protect against pitting and corrosion, which cause radiator leaks Combination of natural and synthetic components provides the ability to seal leaks up to 0.020" x 0.5" Seals even large leaks without interfering with the flow through the radiator or heater core Stops the leak as well as the corrosive condition that causes it