How to Solve Fogging on Car Windows?
4 Answers
If the fog inside the car is not too heavy, opening the windows on both sides will gradually make the fog disappear. Selecting the appropriate air conditioning setting can also help by using the air blown out to defog. Applying anti-fog spray on the inner and outer surfaces of the windows can prevent water vapor from condensing into a fog layer.
Last time when I was driving my kid to school, the windshield got completely fogged up and it was really frustrating. I figured out a few practical solutions. Turning on the heater works best—after starting the cold engine, just direct the vents toward the windshield and pair it with the AC for better dehumidification. Keep a chamois towel in the car to wipe off the fog in emergencies. The key is to remember to turn on the external air circulation to expel the moisture—using internal circulation on rainy days just makes it harder. I also tried applying a diluted dish soap solution on the inside of the glass; wiping it down kept fog away for a week or two, and it works for side mirrors too. Once, when stuck in traffic and feeling stuffy, I cracked the window slightly for ventilation instead of using the AC to save fuel, and it surprisingly helped prevent fogging. Feel free to give these methods a try.
After more than a decade in auto repair, I've found that fogging is essentially condensation caused by temperature differences, with the key being to control cabin humidity. Remember to use the MAX button (the fan-shaped one) on the AC panel—pressing it automatically activates the AC for dehumidification. For long-lasting results, check if the cabin air filter is moldy or clogged, as poor filtration makes humidity control difficult. During rainy seasons, it's best to frequently use the external air circulation mode; using recirculation traps all breath moisture inside. If you notice reduced airflow from the defogging vents, it could indicate frozen evaporator coils or a faulty heater control valve. In vehicles with seat heaters, the rear windshield may sometimes fog up—check if the defogger wires are burned out. As a side note, don't cheap out on anti-fog sprays; inferior products can corrode the chrome trim on vents.
Experienced long-distance drivers all know the three essential tricks to prevent fogging: 1st gear warm air blowing on the windshield + external circulation + AC light on. In winter, don't turn on the heater as soon as you get in the car—wait until the coolant temperature gauge reaches the middle line before setting it to 25°C, otherwise the windshield will get blurrier the more you blow. Don’t hesitate to turn on the AC when it rains, as dehumidifying is more critical than heating. If the AC is broken in an emergency, lower both side windows by two fingers' width to create airflow—it’s quieter than opening all four windows and keeps rain out. Keeping a bottle of anti-fog spray is quite handy; one application can last half a month, but remember to wipe it in circles until completely clear. Foggy side mirrors are even more dangerous—if they don’t have a heating function, apply some soapy water as an emergency fix.
