An undamaged windshield is built to handle heat and cold. Weather cracks almost always start at an existing chip, at a weak point near the edge, or after a sudden temperature change. In Michigan, Indiana and Illinois, the first hard freeze and the hottest summer days are when we see the most new cracks.
Can cold weather crack a windshield?
Yes, when the glass is already damaged. Water inside a chip freezes overnight and expands, pushing the break outward. Blasting the defroster on full against frozen glass, or pouring hot water on it, heats one area much faster than the rest, and that stress can turn a small chip into a long crack.
Can heat crack a windshield?
Strong sun can heat a windshield well above the outside temperature, especially over a dark dashboard. Turning the air conditioning on full and aiming it at hot glass creates the same kind of uneven stress. Undamaged glass rarely cracks from heat alone, but an existing chip often spreads on a hot day.
What a stress crack is
A stress crack starts without any impact point, usually near the edge of the glass. Temperature swings are a common trigger. Stress cracks usually mean a windshield replacement.
How to protect your windshield in winter
- Start the defroster on low and raise it gradually.
- Use a plastic scraper, never a metal one.
- Never pour hot water on frozen glass.
- Get chips repaired before the first hard freeze.
How to protect your windshield in summer
- Use a sunshade or park in the shade when you can.
- Cool the cabin gradually instead of aiming full air conditioning at the glass.
- Get chips repaired before they spread.
Got a chip before winter or a crack that is growing? See how to stop a windshield crack from spreading.