Can extreme heat or cold break car windows? – Jalopnik

As unlikely as it may sound, newscasters in the United States have noted cases of car windows cracking or breaking without any impact. Points of sale such as News 8 reported that cars left outside in the heat developed cracks in their windshields. These cracks appeared almost out of nowhere, and in some cases they appeared as soon as drivers turned on the air conditioning.

The cause of the problem is an uneven temperature change. When a car is left in direct sunlight, the glass and metal surfaces heat up at different rates. This causes built-in stress before the car ever hits the road. When cold air from the air conditioner hits the interior surface, one side of the glass cools unevenly and shrinks too quickly. That stress has to go somewhere, and any little chips or weaknesses become general breaking points.

KOCO 5 News in Oklahoma also reported that auto glass stores received multiple cases of shattered windshields. These occurred during heat waves, with outside temperatures reaching triple digits. Cold winters bring the same kind of risk. Freezing temperatures outside can cause the glass to contract, and if the defrost activates in the vehicle, heat can be introduced unevenly to only one side of the window. Just like with air conditioning on hot days, this creates enough internal stress to cause it to crack or break.

Not all automotive glass reacts the same way to extreme temperature changes, and that difference explains why some drivers notice slowly growing cracks, while others come back to a car filled with loose glass. The windshield is designed to break gradually. Laminated glass is used, which consists of two layers of glass bonded together. Temperature changes do not affect the glass evenly because both layers expand and contract at different rates. This creates tension within the connected layers, and that tension moves to the weakest part of the glass, likely where a small crack already exists.

Rear and side windows do not work this way. These windows are normally made of tempered glass, which is designed to release all stored energy immediately when it reaches the voltage limit. This is why drivers hear a loud bang or pop when the glass breaks. Unlike the windshield, the window or rear window does not crack first, but cracks immediately. This process of cracking and shattering is accelerated if there is already an often unnoticeable chip in the windshield, window or rear window, because the chip itself applies extra pressure.

Once the mechanisms are understood, the patterns behind these failures are easier to avoid. Repairing the small chip in time is one of the easiest ways to prevent your window from cracking or shattering. You can take it to a mechanic or fill the chip with resin yourself. For larger cracks, you may need to replace your windshield, but that could cost you a fortune. In addition, car windows tend to fail during rapid temperature changes, rather than when exposed to constant extreme temperatures. As long as you avoid the air conditioning in the car breaking down while it has been in extreme heat for a long time, you will not cause a disaster.

Ventilate the cabin by lowering the windows and allowing the interior temperature to drop gradually before turning on the air conditioning. Parking in shaded areas or garages also reduces the amount of thermal stress that builds up while the car is stationary. Cleaning habits are also important; spraying cold water on glass that is already hot can cause the same kind of rapid temperature change that leads to stress cracking. Using lukewarm water reduces that risk.

In cold weather the problem is reversed, but you must stick to the same philosophy. If you immediately turn on the defroster or pour hot water on an icy windshield, one side of the glass will heat up much faster than the other. Using a low defrost setting and removing ice with the appropriate scrapers ensures gradual heating of the glass, preventing breakage.