"I dont know how this got into discussing Antifreeze,"

I mentioned it, but that was in another thread.

"but you are supposed to mix it 50-50. They claim that 100% antifreeze can freeze."

Whoever claimed that is an idiot. Don't listen to them. Actually anytihng can freeze, but that is not what they meant. The statement indicates they're totally
unfamiliar with chemistry and physics.

I see a whole bunch of charts on the net, which show the freezing
temperature of various glycol-and-water mixtures.

For ethylene glycol, there's a very clear eutectic effect taking
place. The freezing point decreases from 0C to -50C, as the
concentration of EG in in the mix increases from 0% to about 65%. At
ratios above that (more than 65% EG, less than 35% water), the mixture
freezes at increasingly _higher_ temperatures. The freezing point of
100% ethylene glycol is shown as being around -20C, or not much "below
zero" Farenheit.

The curve for propylene glycol is very different. A mixture of PG and
water freezes at a few degress higher than an equivalent EG/water mix,
up to that magic 65% ratio... but the freezing point continues to drop
(slowly) all the way up to 100% PG. There's no visible eutectic
effect that I can see. However, the rate-of-decrease is quite low
above about 70% - going all the way up to 100% PG gains you only a
couple of degrees of increased freeze protection.

So, the question of "what's the right mix of antifreeze and water, for
the best freeze protection" depends very much on *WHICH* glycol is in
the antifreeze. I suspect a mixture of the two may have a more
complex behavior.

If you're starting with a 100% (or close to it) ethylene glycol
antifreeze, then the advice to stick to 50:50 looks very good, as far
as freeze protection is concerned. If you go up to straight 100%
glycol, you're good down to around -10F or -20C, but below that, the
glycol *will* freeze. You'd save money and have significantly better
freeze protection with 60:40 or 70:30.

If you're using propylene glycol, loading up to 80% or more won't hurt
your freeze protection... but it's still not as good protection as
you'd get with a 60:40 or 70:30 EG mixture.

As for antifreeze, if there is no water at all in there it is much less likely to form corrosive components. There is a difference in how it cools though, thus :

Keeping it absolutely dry is going to be difficult in practice. It's
going to absorb at least some moisture via the reserve tank, I
imagine.