Recycling symbols 1 and 2 are for polyethylene, low density and high density, IIRC.
Another fluid mix you may wish to investigate further is hydrogen peroxide and water at 50:50. That's a lot stronger than the stuff you'll get in the drugstore and I'm not sure how metals would like it. It's a pretty strong reducing agent, so might tend to eat metal for lunch. All I can tell you is that its heat transfer properties are pretty good.
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