Sorry I should have clarified, that I did not drain the system completely. I put in about 7 quarts of what was sold as pure anti-freeze. There was still at least 3 quarts of coolant/water mix still in the system. The stuff I bought lists water on the label, but I have been unable to determine how much water is in it. The label on the jug goes to 75% / 25% which should yield -69 degrees. It tested to -22 tonight. Figure that one out?
Running pure anti-freeze in cold climates is more common than a lot of people think. When I lived in Montana it was the first hard lesson that place taught me. You cant buy antifreeze, as far as I could find, without some water already in it. So figuring out your ratio's is next to impossible.
Also some of the newer anti-freezes use Propylene Glycol and the pure stuff freezes at -74 and is way less toxic.