Whoops, a little late to the party for this thread BUT....I fing this home brew deicer amusing...and a waste of money.
A 16oz bottle of 70% isopropyl alcohol is $2.25, a bottle of Walmarts house brand windshield fluid rated for -20° is $1.60. First, minus 20° is extremely cold and rare when the ambient temps get that low....I'm along the Illinoiz/Wisconsin state line, it gets really nasty at times during the winter yet we can go many years at a stretch without ever seeing it that cold even for a brief hour peak as the over night low, that said "do you really need more???" And that said, and this is where I suspect some of you have had problems with the fluid freezing, is that not all blue washer fluid is a de-icer. A lot of it is simply a cleaning solution for 32° and up. Pay attention to the label of what your grabbing off the shelf. Most often the only difference (within the same brand) is just the number of how low it's good until. I almost made that mistake, grabbed a couple bottles and threw them in the cart. At the check out putting them on the belt side by side I just happen to catch it, one had -20º the other 0º, no different colors, no different designs. Why they make the two, I haven't a clue! In the summer I see the same brand/label with a +30º.
OK so now you figure you'll play junior alchemist and mix up a batch with rubbing alcohol, so you waste time with pouring from one bottle to another, try and keep things pretty much measured right, hopefully you didn't spill and make a mess. Then you have to do this each and every time you run out. Much much easier and a no brainer to grab a bottle of the -20° or in the extremely rare instance you need more get the ready to go -35° juice. Yeah that stuff is usually more per gallon BUT when you get even the cheaper stuff at $1.60 a jug and add a pint of rubbing alcohol at $2.25 (at least) you bumped your cost to roughly $3.50 a gallon. You gain absolutely nothing with this home brew stuff, maybe even waste some money, definitely wasted time and effort.