If you have an open container of antifreeze, it will last indefinitely. Antifreeze is a glycol-based coolant that contains corrosion inhibitors and other additives to help protect your car’s engine. It’s important to keep in mind, however, that once antifreeze has been mixed with water, it only has a shelf life of about two years. So if you have an open container of pre-mixed antifreeze, be sure to use it within two years or discard it and get a new one.