Quote Originally Posted by baludoy View Post
Do leftover coolants get "spoiled " when stored as proper as can be? Meaning it's not exposed to sunlight, it's stored in a cool and dry place, its bottle cap is screwed on tightly, etc.
Many years ago, I bought a 4-liter Toyota Super Long Life Coolant. I only use it for top-ups. Years later, I saw shimmering substance and other sediments collecting at the bottom of the jug. It seems that the additives have separated and so, the coolant is no longer usable. I only kept it in my workshop which is mostly pitch dark when I'm not using it.

My recommendation is, buy just enough of it and throw it away after a year it's been opened.... or as soon as you see sediment at the bottom of the container.