Can Extreme Heat Or Cold Break Car Windows?

As improbable as it sounds, news anchors across the United States have noted cases of car windows cracking or shattering without any impact. Outlets like News 8 reported that cars sitting outside in the heat received cracks in their windshields. These cracks appeared almost out of nowhere, and in some cases, they showed up as soon as drivers turned the air conditioning on.

The root of the problem is uneven temperature change. When a car is left in direct sunlight, its glass and metal surfaces heat up at different rates. This produces built-in stress before the car ever hits the road. When cold air from the A/C hits the inside surface, one side of the glass cools down unevenly and shrinks too quickly. That stress needs to go somewhere, and any little chips or weaknesses become common breaking points.

KOCO 5 News in Oklahoma also reported that auto glass shops received multiple cases of shattered windshields. These happened during heat waves when temperatures outside reached triple digits. Cold winters pose the same kind of risk. Freezing temperatures outside can cause glass to contract, and blasting the defroster inside the vehicle could introduce heat unevenly to just one side of the window. Like with the A/C on hot days, this creates enough internal stress to crack or shatter it. 

Not all auto glass responds the same way to extreme temperature changes, and that difference explains why some drivers notice slow-spreading cracks while others come back to a car filled with loose glass. The windshield is designed to fail gradually. It uses laminated glass, which consists of two layers of glass bonded together. Temperature changes don't affect the glass uniformly, as both layers expand and contract at different rates. This creates tension within the bonded layers, and that tension moves towards the weakest part of the glass, likely where there's already a slight crack present.

Rear and side windows do not act in this manner. These windows are normally made of tempered glass, which is designed to release all the stored energy instantaneously when it reaches its stress limit. This is the reason why drivers hear a loud pop or bang when the glass shatters. Unlike the windshield, the window or rear glass doesn't crack first, but shatters immediately. This process of cracking and shattering is accelerated if there's an often unnoticeable chip already present in the windshield, window, or rear glass, as that chip is exerting additional pressure on its own.

Once the mechanics are understood, the patterns behind these failures are easier to avoid. Fixing the small chip in time is one of the simplest ways to prevent your window from cracking or shattering. You can either take it to a mechanic or fill the chip yourself with resin. For bigger cracks, you may need to replace your windshield, but that might cost you a fortune. Besides, car windows tend to fail during rapid temperature changes, not while they're sitting at steady extremes. As long as you avoid blasting the A/C inside the car while it's been sitting in extreme heat for a long time, you won't be setting the stage for disaster.

Air the cabin out by letting the windows down and allowing the interior temperature to drop gradually before turning the A/C on. Parking in shaded areas or garages also reduces how much thermal stress builds up while the car sits. Cleaning habits matter too; spraying cold water onto glass that's already hot can create the same kind of rapid temperature change that leads to stress cracks. Using lukewarm water instead reduces that risk.

Cold weather flips the problem, but you should stick to the same philosophy. Immediately cranking the defroster or pouring hot water onto an icy windshield will force one side of the glass to heat far quicker than the other. Using a low defrost setting and clearing ice with proper scrapers allows for gradual warming of the glass, helping to avoid any breakage.