I'm not an expert but 20F is not really that cold when it comes to
antifreeze.  A 70/30 ratio of water to coolant would be more than
adequate to get you through that.  According to the chart (I'm assuming
you're using ethylene glycol) that ratio should be good down to about 5
degrees.  That's assuming it's well blended and you don't have any
"pockets" of nearly pure water or coolant anywhere in the system.

It is interesting that the freeze point of a water/antifreeze mix drops
as the amount of antifreeze goes up, to about a 40/60 ratio of water to
coolant.  A higher ratio of coolant beyond that actually provides less
freeze protection; undiluted (pure) antifreeze will actually freeze at
about 10F according to that chart.

Allan
--
1991 Vanagon GL

Mark <mbrush@GMAIL.COM> writes:

> So here's a question - maybe an easy one... So I'm in the middle of a
> flush-n-fill with ye olde bus.  I've probably got something like 70%
> distilled water and 30% coolant in there at the moment (given that it's hard
> to flush ALL the coolant out).  I can't drain and refill with a 50/50 mix
> until the weekend.  But I live in Michigan and it's getting COLD!  Supposed
> to get down to 20 degrees F on Friday morning.  Am I doomed?  Will the
> water/coolant in the van freeze and cause damage? Or will it just get slushy
> and I'll be o.k. until Saturday?  I tested the coolant and the floaty balls
> tell me I'm good until 20 degrees F.
>
> I found this info and chart from the Alaska Science Forum to be kind of
> neat.  Apparently, higher coolant mixes don't necessarily mean better
> protection:
>
> http://www.gi.alaska.edu/ScienceForum/ASF6/680.html
>
> thanks for you thoughts!