What Causes Water Vapor Inside Vehicle Headlights?

2 Answers
SanMary
09/08/25 7:45am
When the headlights are turned on, the fog will dissipate through the vent pipe along with the heat, or it may occur after the vehicle has driven through water or after washing. Below is relevant information: Automobile: According to the latest national standard in China, "Terms and Definitions of Automobile and Trailer Types," an automobile is defined as follows: A non-track vehicle powered by an engine, with four or more wheels, mainly used for: transporting people and/or goods; towing vehicles that carry people and/or goods; special purposes. Vehicle Identification Number (VIN): The Vehicle Identification Number (VIN) has global universality, maximum information capacity, and retrievability, and has become the unique "ID card" for identifying vehicles worldwide. The VIN consists of a group of letters and Arabic numerals, totaling 17 digits. From the VIN, one can identify the vehicle's country of production, manufacturing company or plant, vehicle type, brand, model series, body style, engine model, model year, safety device model, inspection digit, assembly plant name, production sequence number, etc. Once a VIN is assigned to a vehicle, its code will accompany the vehicle through registration, insurance, annual inspections, maintenance, repairs, until recycling and scrapping.
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DelGiselle
09/20/25 6:12am
I've been working in an auto repair shop for several years and frequently encounter issues with foggy headlights. Moisture inside the headlights is mostly caused by aging or cracked sealant, or improper installation where rainwater seeps through gaps. When there's a significant temperature difference, the outer part of the headlight housing is cold while the inside is warm, causing moisture to condense into water droplets. The ventilation holes, designed to balance internal and external pressure and expel moisture, can worsen fogging if clogged with dirt or leaves. This isn't just a superficial issue—it reduces brightness when the lights are on, impairs visibility, and prolonged water accumulation may even cause short circuits. It's advisable to regularly clean debris around the ventilation holes. If the seal is visibly damaged, take it to a repair shop for new sealant or a complete headlight replacement to ensure safe nighttime driving.
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