Mannol 9966 Radiator Leak Stop 325ml is a professional coolant sealant designed to protect and restore the efficiency of your engine’s cooling system. Formulated using advanced metal polymers and fiber blends, it seals micro leaks in radiators, gaskets, hose clamps, cylinder head gaskets, water pumps and engine blocks. This leak stop hybrid formula only activates at leak points, ensuring it won’t block cooling tubes. Compatible with any coolant or plain water, it rejuvenates rubber seals and gaskets, restores elasticity, halts corrosion and prevents future leaks. Easy to use with a full 325ml dose per 12L cooling systems—simply add to the expansion tank, idle engine for 10 minutes and ready to go. Ideal for preventative maintenance, emergency repairs and long term reliability of cooling systems.