If you keep the coolant concentrate in the original container, it can last indefinitely. As long as the container is not exposed to heat and sunlight, it’ll be safe. But if what you have is a premixed coolant, it can last between one and five years in its original container. You should not risk using an expired coolant in your car. As the coolant gets old, it loses the ability to regulate the boiling point of the water and inhibit its corrosive nature. And to make matters even worse, expired coolants themselves turn acidic and corrode the engine and related parts.