Goss Chem-I-Weld Stop Leak 325ml is a chemical welding compound designed to repair and permanently seal small cracks, flaws, porosity and other indents in your car's cylinder heads, engine blocks and other engine castings. Chem-I-Weld is useful for sealing up all brass, bronze, steel, iron and aluminium castings. It is not designed to fix leaks in gaskets, radiators or hoses. It is important cooling system is flushed throughly and refilled with clean water before use.