Your BMW 325i headlights are designed to give you maximum visibility at night and during foggy or hazy weather conditions. But as they are constantly exposed to various pollutants, different weather conditions, heat that emanates from the engine, harmful UV rays, and even time and age, you will encounter a number of headlight troubles. It will be good to know the causes so you will be able to avoid them as much as you can.
Driving at night or through cold, snowy or rainy weather puts your headlights in a difficult situation, especially if you have faulty sealants. The headlight assembly is an area where heat that comes from the engine and cold air that comes from the external environment meet. And you know what cold air does to water vapor-turns it right into the moisture that you can see inside the lenses, blocking useful light. In addition, leaks in headlight washers in certain models are also to be blamed for this. Familiarize yourself on how to take off the headlight assembly so you can clean the inside and apply more effective sealants.
In the past when headlights were made of sturdy glass material, headlight oxidation did not happen. But nowadays, manufacturers turn to polycarbonate plastic because it can easily be shaped to conform to the design of modern vehicles, and it is also cheaper and lighter. But with much exposure to weather, salt, and harmful UV rays, the surface of the headlights gets oxidized, giving it a pitted yellow, hazy appearance.
Your BMW 325i headlight bulbs use xenon gas to emit bright light and are made to last 2,700 hours. But just as normal bulbs expire, so the HIDs also expire. There are a number of possible causes for this: bulb burnout due to age and use, damaged housing, loose power wiring, faulty ballast, and a dying battery that causes power dips. Another major cause of HID bulb failure is touching the bulb with exposed hands when cleaning up the inside of the headlight assembly. The oil from the fingerprints will eventually cause the bulb to shatter. So when you opt to clean the inside of the lenses, always use gloves or a piece of clean cloth when handling the bulb.