No, you should never pour hot water on a frozen car window. This is one of the quickest ways to crack or shatter your windshield or side glass. The reason is a phenomenon called thermal shock. When boiling water (212°F / 100°C) hits ice-cold glass (which could be below 0°F / -18°C), the extreme and rapid temperature difference causes the glass to expand unevenly. Since glass is a poor conductor of heat, the outer surface expands much faster than the inner layers, creating immense stress that exceeds the glass's tensile strength, leading to a crack.
The cost of this mistake is significant. A simple crack often requires a full windshield replacement, which can cost between $250 and $600 or more, depending on your vehicle's make and model, especially if it has advanced features like rain sensors or advanced driver-assistance systems (ADAS) that require recalibration.
| Common Consequences of Using Hot Water on Car Windows | Estimated Repair Cost (USD) | Likelihood |
|---|
| Minor chip or crack (repairable) | $50 - $150 | Low |
| Long crack requiring full windshield replacement | $250 - $600 | High |
| Complex windshield replacement (with ADAS recalibration) | $600 - $1,500+ | Medium |
| Shattered side window replacement | $200 - $500 | Medium-High |
| Potential damage to window trim/molding | $100 - $300 | Low |
The safe and correct method is to use your car's defroster. Turn on the front and rear defrosters, set the fan to high, and use the A/C to dehumidify the air, which helps clear the ice faster. While the car warms up, use a plastic ice scraper and a de-icing spray (typically a mixture of isopropyl alcohol and water) to gently remove the ice. A mixture of two-thirds isopropyl alcohol and one-third water in a spray bottle is an effective homemade de-icer. Always allow the car's heating system to do most of the work to avoid any risk of glass damage.
