I know this is wierd, but I have an older bottle of ST blue outside and it froze at about +20f! I had poured some into my nephews car, so I pumped it out and refilled with new. I had a wierd feeling when I used it, not shure if it was car wash or what, but definately not because carwash is not blue. It froze solid. Funny story everyone hee should know, is how the Russian Mob smuggled dyed-blue vodka into somewhere, in washer fluid bottles. They could get the blue colour out later somehow. I still keep a bottle of "washer fluid" under the seat.