Coolant shelf life

[Still_Running]

Don't worry about using it, as far as I know it is good indefinitely in the container whether its been opened or not but you can also test it with the tester. It degrades over time when in the car cooling system by engine heat probably the worse with driving in high heat climates where temperatures of engine and pressure builds-up such as in congested city driving as well just because of contact with metal of engine components over time. Prestone premium product says its good for 15 yrs/ 150,000 miles. My hunch is that when in the cooling system its cold weather job it does by keeping the coolant from freezing is the least of the cause of breakdown over its yrs of use. You'll probably flush the system and replace the coolant on a schedule your manual indicates. Which is probably quite a long time if its a newer car but some suggest doing it every 5 or so yrs no matter what the manual says.