Hot Water
It is widely discouraged to pour hot water onto your frozen windshield. This is because the contrast between hot and cold is too big, which can cause the windshield to crack when there’s already a tiny fracture in the glass. What happens is that a little bit of water gets into the small fracture or crack, and this water will expand when it freezes. That way, a tiny fracture can turn into a huge crack. That’s why you should only use this trick if your windshield is still entirely in one piece. Always use lukewarm water and never hot water.
