When you start your car up in the morning, the water and antifreeze mixture in the radiator is pumped through channels in the engine to reduce heat. The mixture is then returned to the radiator to be cooled by fresh air. This cooling circuit prevents your engine from overheating, and it provides your heating system with a source of warmth. Water boils at 212 degrees Fahrenheit and freezes at 32 degrees Fahrenheit, which means a car cooled by H2O alone would overheat very quickly and could not be driven at all in freezing temperatures. 

Antifreeze is a chemical additive that lowers the freezing point of water and increases its boiling point. Thanks to antifreeze, your car will run reliably in very cold or very hot environments. The active ingredient in most antifreeze is either propylene glycol or ethylene glycol. Check your owner’s manual to find out which type the manufacturer recommends for your car. Here are some reasons why you need to make sure your cooling system contains the correct mixture of antifreeze and water. 

• It prevents freezing: Ice is any engine’s worst enemy. Expanding when it freezes, water can rupture coolant hoses and crack engine blocks. A 50-50 antifreeze mixture lowers the freezing point of water to minus 35 degrees Fahrenheit, and a 70-30 mix will remain a liquid at minus 83 degrees Fahrenheit. 
• It improves heat transfer: Antifreeze raises the boiling point of water as well as lowering its freezing point. This means that an antifreeze and water mixture will absorb heat from engine components much more efficiently. A 50-50 mixture of water and antifreeze has a boiling point of 223 degrees Fahrenheit. 
• It fights corrosion: Rust forms when water, metal and oxygen get together. The liquid in your cooling system is pumped through tiny channels in your engine, but it doesn’t cause any corrosion. That’s because the antifreeze it contains has additives like phosphates and nitrates that protect engine components and prevent rust from forming.