Bar's Leaks Heavy Duty Radiator Stop Leak, No. PLT11, features patented Rhizex pellets that dissolve in minutes to seal cooling system leaks. Bar's Leaks Heavy Duty Radiator Stop Leak also conditions the cooling system, is compatible with all brands of antifreeze, and works safely and effectively on plastic, aluminum and metal radiators, heater cores, blocks, heads, gaskets and freeze plugs.