Originally Posted By: bprat318
In my vehicles right now is your normal +32 degree fluid, all of them are at least half full in not more, I don't see myself using up all this stuff before it gets really cold outside, so my question is as follows. If I were to mix in one bottle (about 16oz) of 99% Isopropyl alcohol (rubbing alcohol) with the washer fluid would it lower the freezing point to where it would be good to use even in a Wisconsin winter? Would there be any negative affects to my windshield, wipers or pump and tubes? Am I crazy for thinking of this?
I researched this exact issue not too long ago...
The link below shows the freezing points of various isopropanol/water mixtures
http://www.engineeringtoolbox.com/ispropanol-water-d_988.html
As you can see, you'd have to add quite a lot of isopropyl alcohol to reduce the freezing point to typical Wisconsin winter temperatures.
A better solution is to add straight methanol.
http://www.engineeringtoolbox.com/methanol-water-d_987.html
According to this chart, you can reduce the freezing point to about 0°F by mixing about 24% methanol (by volume).
FYI, the good, winter-blend washer fluid is typically about 35%(w/w) methanol in water, or about 40% by volume. So adding methanol to your washer fluid is not harmful at all to any part of your car.
One cheap way to buy straight methanol is to buy HEET gas line anti-freeze/water remover. The yellow bottles with blue writing, $1.58/12oz or $5.97/48oz at walmart. Add two bottles to a half gallon of +32 will give you a freezing point of about -5°F. Three bottles will take you down to about -15°F, four closer to -25°F.
Of course at that point, your (now 3.5 quarts) of washer fluid now cost you about $6.50. It is much cheaper to just squirt out ALL the +32 and re-fill with the $2.50/gal winter grade stuff.
EDIT: Isopropyl alcohol will not harm anything, it has similar solvency properties to methanol.
Your 16 oz of drugstore-grade isopropyl alcohol (actually probably 91%, not 99%) in a half gallon of +32 washer fluid, would reduce your freezing point to around +21°F.