How to Deal with Fogging on the BMW 3 Series Windshield?
3 Answers
Press the defogging button, turn on the air conditioning cooling (A/C) switch, set the temperature to the lowest, and turn on the external circulation to defog. Both cold and warm air can be used to defog the car glass, but warm air is slower than cold air. The most effective method is to use cold air, which blows dry cold air directly onto the glass, preventing water vapor from condensing on the glass and achieving the purpose of defogging. The method of using warm air to defog is the same as using cold air, but it should be noted that warm air should not be used for defogging on rainy days as it will initially increase the fog. When the car glass fogs up, the external circulation should be turned on. The reason for car glass fogging: There is a certain temperature difference between the inside and outside of the car. If the temperatures inside and outside the car are different, the surface of the side with the lower temperature will have a saturated vapor pressure lower than the vapor pressure of the surrounding environment, causing water vapor to gather on the glass surface and form tiny water droplets, resulting in fog. Methods to defog car glass: Air Conditioning Cooling: Use the air conditioning cooling and dehumidification function to reduce air humidity and remove fog. In summer, especially when multiple people enter the car and the air conditioning is not turned on in time, the exhaled air has high humidity, and the windshield will fog up quickly. At this time, you can turn on the air conditioning to blow cold air onto the windshield and use the dehumidification function of the air conditioning to remove the fog on the windshield quickly. However, if the humidity is too high and the air conditioning effect is not obvious, you can slightly open the window to quickly reduce the humidity inside the car. Of course, it can also be used in combination with the air conditioning for faster results. Air Conditioning Warm Air: Use the method of reducing the temperature difference to remove fog. In winter, use warm air to blow hot air onto the glass to quickly raise the temperature of the windshield and reduce the temperature difference between the inner and outer surfaces of the window glass, which can prevent excessive fogging on the windshield in time. However, it should be noted that the rear and side glass temperatures rise slowly, so it takes a longer time to remove all the fog. Whether it is automatic or manual air conditioning, turning on the air conditioning is beneficial for dehumidification; the air conditioning temperature control should not be set to the coldest position, otherwise, the outer surface of the windshield will easily fog up after prolonged defrosting. Spraying Anti-Fog Agents for Prevention: Spray a small amount of defogging agent on the car glass window and wipe it clean to remove dirt and stains on the glass window. While polishing the glass, a thin transparent protective film is formed on the glass, which can effectively prevent water vapor from condensing on the glass and forming a fog layer, especially suitable for cold winters. Alternatives to anti-fog agents include dishwashing liquid, soapy water, glycerin, alcohol, or salt water. After drying, wipe off excess fibers with chamois or a soft dry cloth, which can ensure that the car glass does not fog up for several days. Opening Windows for Convection: If the fog inside the car is not heavy, you can open the windows on both sides to create convection between the inside and outside air, reducing the temperature difference, and the fog will slowly disappear. The principle of this method is the same as using cold air from the air conditioning. The disadvantage of opening windows for convection is very obvious: it cannot be used in rainy or snowy weather, on highways, or when the fog is heavy.
I often encounter fogging issues on the windshield when driving my BMW 3 Series, especially during rainy or cold weather when humidity is high, leading to condensation. The first thing I do is press the front defogger button on the car, which is prominently located on the climate control panel—this is a dedicated defrost function designed by BMW. Once activated, the air conditioning automatically switches to maximum airflow directed at the windshield and adjusts the temperature to balance the interior and exterior temperature differences. Within a few minutes, the fog dissipates. If the effect isn't obvious, I also turn on the fresh air mode (external circulation) to let in outside air, which helps reduce interior humidity. For prevention, I run the external circulation for a few minutes before turning off the AC when parking, keep the inner side of the windshield clean to avoid residual oil film, and refrain from driving until visibility is clear in cases of severe fogging—safety always comes first.
From a driving perspective, windshield fogging is essentially caused by condensation due to large temperature differences combined with high humidity. In a BMW 3 Series, to quickly defog, the first step is to immediately turn on the air conditioning system after starting the vehicle, press the defrost button or adjust the air direction to blow onto the windshield. It will adjust the temperature to a moderate level, typically around 20 degrees Celsius, using the external circulation mode to introduce dry air, with the fan set to level 3 for optimal effect. Remember to check if the air filter is clogged, as excessive dust accumulation can affect ventilation efficiency. Develop a habit of clearing moisture sources like umbrellas or wet clothes before getting in the car to reduce fogging frequency. If visibility becomes unclear while driving, pull over to address the issue instead of pushing through.
