Get down Lidl in the autumn and get some of their -60°C screenwash. Diluted 50:50 it never gives any problems with freezing. Stripping paintwork maybe (or breaking windscreens*), but freezing, no
* Had a tiny (and I mean tiny, like the size of small childs's small finger nail cutting!) chip in the screen on our Xsara Picasso. SWMBO had sat in it with the engine on at about -10 for 3/4 hour as No 1 son was asleep. We then went out in it, and I washed the windscreen. BANG! Cracked it from side to side across the chip
