Coolant loses its anti-corrosion properties over time, so its a good idea to do a cooling system flush every few years. Knowing how to flush a radiator could save you some money and prevent a trip to the breakdown lane. Depending on your car you'll need 1-2 gallons of antifreeze and 1-2 gallons of distilled water (or 2-4 gallons of premixed antifreeze), a working garden hose, and a bucket. Because antifreeze is toxic you should also wear gloves and eye protection. Before starting work on a car's cooling system ensure that the engine and coolant are cold – it can take several hours after driving for the car to cool down completely.
Remove the cap from the expansion tank or radiator and check its condition. Replace the cap if its broken or looks as though it won't seal properly (most coolant systems work under pressure). Locate the drain cock on the bottom of the rad and loosen it to allow the old antifreeze to empty into the bucket. If there is no drain you may need to remove the lower radiator hose. Check all the hoses for cracks and bulges and replace any that show signs of wear. Once the radiator is empty close the drain cock and properly dispose of the coolant. Antifreeze should not be left around or poured down a drain as it is poisonous and attracts animals.