Antifreeze can remain effective for two to three years of use, or roughly 36,000 miles. For the best results, antifreeze should be changed every two years, or sooner if excessive use and mileage causes the liquid to degrade.
Antifreeze is an engine coolant that keeps the heat of a vehicle's engine from melting gaskets or breaking down the oil needed to lubricate moving parts and components. Over time, according to CarsDirect, dirt and other contaminants can enter the vehicle's cooling system, limiting its effectiveness. For the best results, old engine coolant should be replaced every two years, and the cooling system should be flushed as well.