Engine coolant, commonly called radiator fluid or antifreeze, helps to keep your engine running cool. As the coolant passes through the engine it transfers heat from the metal into the fluid. When the fluid reaches the radiator, the fluid cools down due to the cold air flowing past the radiator. Over time, the coolant in the radiator brakes down and you must replace it with fresh coolant.
Remove the radiator cap on the top of your radiator. If your radiator does not have a cap, remove the cap from the fluid expansion tank located to the left or right of your radiator.
Place a drainage container under the petcock located on the bottom of the radiator. The petcock is a drainage valve that lets coolant out of the radiator. In most cases, you can open the petcock using a pair of pliers, but in some cases, you need a socket and ratchet to open the valve.
Drain all of the coolant out of the radiator and then close the petcock.
Check your owner's manual for the brand or type of coolant you must use in your radiator and for the amount of fluid your radiator holds. Different brands of coolant are made of different chemicals. For example, all GM vehicles use DEX-COOL coolant. Using any other coolant will damage those engines. If you cannot locate your owner's manual, consult an auto parts retailer for the information. The cooling system requires two gallons for most sedans, coupes and SUVs, but most large pickup trucks require three gallons.
Pour the antifreeze into the radiator filler spout or the fluid expansion tank if your radiator does not have a lid. Top off the radiator with distilled water, usually about two gallons worth. To avoid damaging your radiator, use only distilled water.
Leave the cap off your radiator or expansion tank, start your vehicle and run it until the radiator fan turns on. Turn off the vehicle and top off the radiator with distilled water. This ensures all of the air is expelled from the coolant system.