Bar's Leaks Carbon Fiber Block Seal Head Gasket & Cooling Sealant, No. HG-1, is a one-step formula to seal coolant leaks that meets ASTM D6107 stop-leak specifications. It repairs blown head and intake gaskets, seals cracked cylinder heads and blocks, stops heater core and radiator leaks, fixes leaking freeze and core plugs, and stops overheating in water-cooled vehicles.