Antifreeze is a liquid added to the engine cooling system to transfer heat away from the engine while running, as well as prevent the engine cooling agent from freezing while shut down during cold weather conditions. If only water was used as the coolant and would freeze if the temperature dropped. It would stop coolant circulation, and the engine would overheat. The coolant is the liquid that circulates through the cooling system, removes waste heat from the engine, and delivers the heat to the heat exchanger known as the radiator. The radiator cools the hot antifreeze taken from the engine then circulates it back to cool the engine. The most commonly used antifreeze is ethylene glycol. A mixture of haft water and half ethylene glycol is the recommended coolant for year-round use in most cars. Additionally, antifreeze is usually green or blue-green with a dye for identification. It allows the antifreeze to serve as a leak detector. The distinctive color makes it easier to locate a leak. Antifreeze also contains additives to help prevent rust and corrosion from within the engine. These include a corrosion inhibitor and a foam inhibitor. Corrosion or rust can shorten the life of metal parts. It also forms an insulating layer that reduces heat transfer from the metal to the coolant.