I'm running ethylene-glycol. So far, no problems with any of the seals being eaten.
(Bottle also mentions diethylene glycol and potassium 2-ethylenhexandate)
Specifically, a mixture of 60% ethylene glycol and 40% water freezes at −45 °C (−49 °F).
That's actually neat. The freezing point of a certain mix, ends up lower than the freezing points of BOTH individually. I can't remember if we covered that in Chem class (10+ years ago!)
And of course, 50% distilled water.
Basically, I picked up a bottle of generic "all car" 50/50 mix, and dumped it in. Ran it for a few weeks out of the system to see if it'd eat any seals, and then installed it.
I don't recommend touching it with your hands (no gloves) though. I'm sure it's toxic, and very sticky... like a sugary (non-diet) soft-drink.
Though the material safety literature/etc shows it's not super dangerous unless you actually drink it:
[edit annoyingly long URL]
[/edit annoyingly long URL]
[when touching] the rate of penetration is so slow that excretion and metabolism
pathways are not overwhelmed. Metabolites do not accumulate, therefore, and toxicity does not occur.
I couldn't find any material details on the seals used from random Chinese fitting sellers. But "meh, !@$! it" happened so I winged it. If I was actually experienced in engineering (as opposed to degree), I'd probably be smart enough to tell the material of an o-ring by feeling it, smelling it, etc.
Oh, and PVC should definitely be rated for EG:
Although, with the bends from gravity/etc, I really could have sprung for the "reinforced PVC" so the tubes wouldn't easily collapse on themselves for future projects. I thought "it's not under vacuum or high pressure so = go cheap" but I didn't think about the small 3/8" tubing collapsing so easily.