I recently needed to top-off the coolant on my car, but only used a part of the gallon-sized 100% antifreeze container that it came in - how long is it worth keeping the rest in my garage for future use? does it spoil/turn acidic? it's in a plastic bottle with an air-tight cap.
note: it is currently un-mixed, would it be better to mix it with water now?
The coolant should not expire any time soon. If it is not in an automobile being used, it is not degrading. With the cap on it, there is nothing contaminating it. From what I was just reading, there is no practical expiration if kept in the original container.
Just went to top off my cooling system and noticed the Anti-Freeze I went to use from the original capped container was black. I've had it for well over 5 years, so apparently it does go bad eventually.
When the word coolant is used in can mean a couple of things. Coolant made up of antifreeze and water out of your household tap, 50-50 solution, would last for around 3 years. Coolant made up of antifreeze and distilled (de-ionised) water, 50-50 solution, should last for around 5 years. Because of the nonsense surrounding 'coolants' always adhere to the instructions on the supply container. If you live in an area of the world subjected to very low temperatures you could look at a coolant change on the outset of winter as a sort of insurance. An antifreeze mixture should only be at a max of 50% as any greater amount of antifreeze will increase the freezing temperature. ie 50% antifreez would be -30C freezing, 60% antifreeze would be -20c.
