Why Are There Water Droplets Inside the Windshield?
3 Answers
In winter, the external temperature of the car is low while the internal temperature is high. The warm air inside the car condenses into small water droplets when it meets the cold glass. Reasons for window fogging: 1. Large temperature difference between inside and outside the car: Due to the temperature difference, the windows are prone to fogging. This happens because the window glass, in contact with the outside, is colder, causing the water vapor inside the car to condense on the glass and form fog. 2. Window temperature below the dew point: At a certain air humidity, if the window temperature is lower than the dew point, condensation easily forms on the surface of the window, leading to fogging on the windshield. 3. Temperature difference between the two sides of the window: If the temperatures on either side of the window are different, the surface with the lower temperature will have a lower saturated vapor pressure than the surrounding environment, causing water vapor to gather on the glass surface in the form of tiny droplets, resulting in fog.
Water droplets on the inside of the windshield are mostly caused by condensation. When there's a significant difference between the humidity inside the car and the temperature, moisture condenses on the cold glass. Based on my extensive experience, common causes include high interior humidity (like leaving windows open during rain), forgetting wet shoes in the car, or accumulated water in floor mats. Aged weatherstripping is a major issue - it allows water seepage through door/window gaps that's often invisible. AC settings matter too - not using recirculation mode or misaligned vents can prevent moisture dissipation, worsening condensation. While using the defog mode can quickly clear it temporarily, long-term solutions involve checking seals and fixing leaks to prevent recurrence and ensure driving safety. Develop habits like regular ventilation and keeping wet items out of the car to maintain clear visibility.
I've encountered several instances of water droplets forming on the inside of the windshield while driving, especially during humid rainy seasons when temperatures drop significantly. It turned out that I had forgotten to fully close a small window when parking, leaving a slight gap through which rain seeped in, causing moisture to accumulate. The result was waking up to a car full of foggy droplets. Upon further inspection, I also discovered that the door seals were slightly loose, allowing water to creep in from below. Another minor oversight was leaving a wet umbrella in the trunk, which contributed to the fogging when left enclosed. A piece of advice from experience: always dry the interior before parking, use the car's heater or air conditioning to dehumidify, or simply open the windows for ventilation. Regularly checking the door frames to ensure the seals are intact can help minimize such annoyances. Safety comes first—obstructed visibility is a serious hazard.
