STP Radiator Sealer is a fast-acting liquid sealant additive formulated with corrosion inhibitors and lubricants to permanently stop micro-leaks across the cooling network.

It is suitable for:

• quickly sealing hairline cracks, micro-punctures, and weeping seams in radiators and heater cores;
• preventing fluid loss around hose connections, coolant flanges, and heater matrix joints;
• all petrol, diesel, and gas engines in passenger cars and light commercial vehicles;
• all radiator materials (aluminium, copper, alloy, plastic) and all types/colors of antifreeze;
• lubricating water pump mechanical seals while protecting metals against rust and scale deposits.

The additive cycles naturally with the moving coolant, solidifying only at points of pressure drop and air contact to form a durable seal. Its clog-free formula ensures full, unrestricted flow through narrow thermostat bypass lines, heater cores, and water pumps. One 300 ml bottle treats cooling systems up to 14 liters capacity; simply shake well, pour into a warm cooling system with the heater set to hot, and run the engine or drive for 10 minutes to set the seal.