Why Does a Car Windshield Crack Spontaneously?
2 Answers
Here are the reasons why a car windshield may crack spontaneously: 1. Spontaneous cracking of car windshields usually occurs at the edges of the glass, mainly due to the internal tensile stress and surface compressive stress generated during the heating and cooling process of laminated glass manufacturing. These forces remain stable when balanced, otherwise spontaneous cracking may occur. 2. If a car windshield is exposed to intense sunlight and then comes into contact with cold water, the excessive temperature variation may also cause the glass to crack. If the windshield cracks spontaneously, you should immediately pull over and stop driving. 3. Other possible causes of windshield cracking include improper installation of the car glass, the use of substandard adhesives, or poor-quality explosion-proof film applied to the glass, which may absorb heat instead of insulating it, leading to excessive temperature differences when the air conditioning is on inside the car.
A friend who has run an auto repair shop for 20 years gave a thorough analysis of spontaneous windshield cracking. He said 80% of cases stem from hidden defects during glass manufacturing, such as nickel sulfide impurities in laminated glass that expand with temperature changes, causing spontaneous breakage. Poor installation techniques also contribute—when the glass is squeezed too tightly by the frame, it loses room to expand. Additionally, we often see windshields damaged by flying stones on highways; even if they don’t crack immediately, the weakened spots remain under stress. Thermal stress is another silent killer—in summer, the glass surface can heat up to 70°C while the AC cools it to 20°C, creating a 40°C+ temperature difference in just 30 seconds, which easily leads to cracking. So, avoid parking under direct sunlight, and promptly repair minor cracks—it’s crucial.
