STP Radiator Flush 300ml contains an advanced formula that cleans the cooling system quickly and effectively. It clears blocked water channels that can cause overheating, removing rust and sludge. Use before changing coolant or adding antifreeze, to help keep your cooling system in optimum operating condition. Safe with all metals, including aluminium, and suitable for all types of radiator. Also safe for rubber hoses. Directions: Shake bottle well and pour entire bottle into radiator. Leave in the cooling system and drive for about 30 minutes. Drain the radiator when cold, flush and refill with appropriate coolant/anti-freeze per manufacturer instructions.