DrewE wrote:

It doesn't generally go bad. The dye may fade or change over time, but the ethanol and/or propylene glycol doesn't break down, at least over the course of a few years, assuming the container is closed so the contents cannot evaporate. If it's a few decades old or has evidence of some weird slime growing or something like that, I'd probably pass, but otherwise it shouldn't be any problem at all.

d3500ram wrote:

If you are concerned about any funk in it, just use it in the toilet and traps and get the fresh stuff for the domestic water supply.

joshuajim wrote:

Seeing as how vehicle manufacturers recommend changing coolant between 100,000 and 160,000 miles which might correlate to 10 years of severe duty, I don't think I would worry much about some virgin coolant in a jug.

joelc wrote:

I am not at home base now, but I use it in my washer which is in my shed when the temps drop. I don't know if it has a expiration date on it. Mine is going on 2 years old and I know that it was good at 1 yr when used last year. Good question. Just thought of something. Take a cup put some in it and see if it freezes in your frezzer?? If it does it goes bad.