[MandK]

-50 antifreeze starts to slush somewhere around 10 degrees. Unlike water, it doesn’t expand or has an extremely low expansion rate when freezing and won’t expand enough to do damage until it’s rated freeze point. I have had -50 antifreeze in my boats systems at -15F and no problems even though the leftover jug in my shed was pretty much solid.
The coldest our Montana has been while winterized was -5F. While using it, 15F.