There are several reasons why a car windshield may fog up on the inside when the engine is running.
High humidity inside the car: When the air inside the car is humid, it can condense on the inside of the windshield when it comes into contact with the cooler surface of the glass. This is especially common on cold days when the temperature difference between the inside and outside of the car is high.
Lack of air circulation: If there is not enough air circulation inside the car, the humid air will become trapped and more likely to condense on the windshield. This can happen when the windows are closed, the vents are blocked, or the fan is not turned on.
Dirty windshield: A dirty windshield can also contribute to fogging, as the dirt and grime on the glass can trap moisture and make it more difficult for the air to circulate.
Coolant leak: In some cases, fogging on the inside of the windshield can be a sign of a coolant leak. If you notice a sweet smell or a white residue on the inside of the glass, it's important to have your car checked by a mechanic as soon as possible.
To prevent fogging on the inside of your car windshield, you can take the following steps:
Keep the air conditioning or defroster on. This will help to circulate the air and remove excess moisture from the inside of the car.
Open the windows or vents slightly. This will allow fresh air to circulate and help to prevent fogging.
Clean the inside of your windshield with a glass cleaner. This will remove any dirt or grime that could trap moisture and make it easier for the air to circulate.
Have your car checked for a coolant leak. If you notice a sweet smell or a white residue on the inside of the glass, it's important to have your car checked by a mechanic as soon as possible.
