Definition: Antifreeze protects the cooling system against both freezing and boiling over. When used at normal strength (50% antifreeze, 50% water), it can lower the freezing point of the coolant to -34 degrees F. and raise its boiling temperature to 276 degrees F. Never use straight antifreeze in a cooling system. Always mix it with at least 50% water. Most antifreeze is 95% ethylene glycol (EG). The only differences between brands of antifreeze are the type and/or quantity of anti-corrosion additives used. Ethylene glycol never wears out but the corrosion inhibitors do. That's why antifreeze should be changed every two years (except for long life antifreezes, which have special additive packages that allow them to go up to 5 years/150,000 miles between changes). For the environmentally concerned, propylene glycol (PG) antifreeze is also available at slightly higher cost. PG antifreeze is less toxic than ethylene glycol.

Related Resources:

Cooling Systems: Part 1
How this important system works and helps your engine keep its cool.

Cooling Systems: Part 2
How this important system works and helps your engine keep its cool.

Antifreeze: Red or Green
Dexcool® or regular antifreeze? Which antifreeze to use and why.