What Causes Persistent Fogging on the Outside of the Windshield?

[SanLeilani]

The reason why the outside of the windshield cannot be defogged may be due to moisture on the exterior after rain. Here are the relevant explanations: 1. Temperature difference between inside and outside the car: Primarily, the large temperature difference between the interior and exterior causes cold air to hit the glass, leading to external moisture condensing on the surface. This is a basic principle of physics. A significant temperature difference between the cabin and the outside or rainy conditions can cause fogging on the windshield and door glass, posing a safety hazard for driving. 2. Precautions: Regularly clean debris and snow near the air conditioning intake to ensure the system functions properly. Generally, the ventilation mode should be set to external circulation to promote better airflow.

[LaPaisley]

I often drive, especially on damp mornings or rainy days, and it really annoys me when the fog on the outside of the windshield won't go away. The main reason is the temperature difference: the heater inside the car is turned up high, while the outside air is chilly, causing the warm air to condense into fog on the glass when it meets the cold. Additionally, high humidity doesn't help—like on rainy days, the fog becomes more stubborn. When the wipers swipe it away, it comes right back, possibly because the wiper blades are old, not cleaning properly, or deformed. Also, if the air conditioning is set incorrectly, such as having the airflow directed straight at the windshield, the cold air can actually make the fog more noticeable instead of eliminating it. I've tried solutions like adjusting the car's air conditioning to blow toward the feet or the front, avoiding direct airflow onto the windshield, and turning on a bit of external circulation to let the air flow. When temporarily parked, slightly opening the windows can reduce the temperature difference between inside and outside, making the fog easier to disperse. If the wipers aren't working well, simply replacing them with new ones is an easy fix. However, this situation seriously affects driving visibility, especially at night, and can easily lead to accidents, so never force yourself to drive under these conditions—find a safe place to address the issue before hitting the road. I think regular vehicle maintenance, replacing wipers, or cleaning the air conditioning vents can help prevent this problem.

[CarterAnn]

This issue is also common in new cars, and I suspect it's due to incorrect automatic settings. Modern vehicles have intelligent defogging systems, but sometimes the sensors respond slowly or the airflow direction is set incorrectly, preventing external fog from dissipating. For example, when the heater is turned on in cold weather, if the system doesn't promptly adjust the air recirculation, humid external air condenses on the warm glass. High humidity is another factor—if the wipers are insensitive or worn out, they may thin the fog but not completely clear it. The solution is manual intervention: check the AC settings to ensure the fan speed is slightly higher and set the airflow to mixed mode rather than focusing solely on the windshield; try activating the defrost button, as some cars have a dedicated external defogging function. Additionally, turn off interior heat sources before parking to allow more even temperature distribution, which can reduce fog buildup. I recommend regularly using glass cleaner to minimize water droplet residue and inspecting wipers frequently—check them every month or two and replace them if damaged. Safety comes first: fogged windows impair visibility, so never force yourself to drive—ensure clear vision before setting off. These practices have helped me avoid several minor accidents.

[EllaLee]

As a daily driver, I particularly dislike fogging on the outside of the windshield, especially during the rainy season when the windshield becomes completely white, making driving quite scary. The main reasons are usually high humidity or excessive use of the car's air conditioning, which creates a temperature difference between the inside (hot) and outside (cold), causing fog to stick to the glass. Additionally, worn or dirty wipers can make things worse by smearing instead of clearing the fog. My advice is to act promptly: while driving, don’t panic—turn on the defroster and increase the fan speed for a few minutes, or crack the window slightly to let air in and balance the temperature. Gently wiping the outside of the glass can also help, but be cautious for safety. Remember to avoid using the recirculation mode in humid weather; instead, use the fresh air mode for better ventilation. Although annoying, prevention isn’t difficult: during maintenance, check the condition of your wipers and clean the windshield to remove any oily residue that might attract fog. Most importantly, never drive with compromised visibility—ensure a clear view for your safety and others’.

[VanJayla]

From the perspective of persistent windshield fogging, I've analyzed common causes. Temperature difference is the main culprit: warm interior meets cold outside, condensing into fog when humidity is high; worn wiper blades or cracked rubber strips reduce wiping efficiency; or incorrect AC settings, directing cold air at the glass, exacerbating the issue. For solutions, my top recommendation is checking wiper condition—replace them if needed and observe improvement; adjust AC to defog mode with increased fan speed, avoiding direct airflow onto exterior glass; brief window ventilation works wonders. I also emphasize prevention: maintain clean windows with regular glass cleaning; minimize heater use during rain, employing external circulation to expel moisture. Overall, unaddressed fogging poses serious risks, especially on highways—address it promptly. Monthly vehicle detail checks are advised to prevent minor issues from escalating.