Storing antifreeze/coolant in a translucent container -- did sunlight make it change color?

I’ve got a big translucent jug in the back of my pickup truck. It’s got about a gallon of antifreeze/coolant** in it (mixed 50-50 with water).

This jug has been sitting in the back of my truck for three weeks now. When first poured, the coolant was a vivid DayGlo lime-green color. After three weeks of being in the back of my truck and baking in the sun fourteen hours a day, the coolant has changed. The vivid green is gone. It’s now the color of super-weak iced tea … kind of a muted straw yellow color. It doesn’t even smell much like coolant anymore – it’s got some kind of an unidentifiable (if faint) chemical smell, not too different from filmsetting chemicals used by home photographers.

So … what chemically happened here? The sunlight did it, didn’t it? I did later think of the fact that coolant is sold in opaque jugs :smack:
** “coolant” on future reference. It doesn’t freeze enough down here to make me think of it as “antifreeze”.

Heat can also destroy dyes, but I guess they select ones that will take the heat. Have you ever seen cheap plastic toys left out in a sand box all summer? Yeah, the sun fades them.

The yellowish-green dye in antifreeze is fluorescein, which is indeed degraded by sunlight. I don’t know what would be degrading the antifreeze, although it usually has additives, which might be unstable in sunlight, or react with the plastic in that bottle.

To be more specific, I am storing it in an empty kitty litter container (this exact brand).

Now that I think of it … this kind of jug was probably not designed to hold liquids (though it’s very stable and does not tip over). Perhaps the cap is not airtight enough, and on top of the sunlight degradation, there’s some kind of oxidation going on.

But then … a car’s cooling system is not airtight, is it? Maybe the pressurized cap on the radiator does make the system airtight, though? Not sure.

A quick google search reveals that alcohols (such as ethylene glycol or propylene glycol) do not absorb UV light in the visible spectrum (above 295 nm), so you wouldn’t have to worry about the active ingredient degrading.