The most common cause of severe headlight condensation is the worn headlight seal between the front transparent plastic and the headlight housing. If not repaired the water ingress will cause the expensive headlight electronics failure.
In most cases, the only permanent solution is to replace the headlight or repair the gasket seal.
Before we move on, let’s first establish if you even need to repair the headlights.
This is a very common complaint by many car owners, not just BMW. Since I often encounter this problem, I will share with you how I solve this problem for my customers.
The Normal vs. Heavy Headlight Condensation
The condensation phenomenon is promoted by damp, humid air that penetrates into the headlamp from the outside by entering through the ventilation system. This then evaporates in the headlamp while it is still warm, and when the unit cools it then precipitates to form condensed moisture on the inside of the headlamp lens (1).
This neither causes corrosion damage to the headlamp nor does it exercise a negative impact on the intensity of the light that it emits.
The formation of droplets on the inside of the headlight unit indicates a headlamp with severe condensation (2).
The presence of moisture after a car has been washed in an automatic car wash or driven in heavy rain can suggest excessive condensation and possibly imply a headlight that isn’t properly sealed (usually occurs only on one side).
Drying The Headlight
Open any accessible bulb cover, turn the lights on and drive the car without the cover for an hour or less, until there is no condensation visible. Use common sense and don’t drive in the rain or take it to a car wash! Also, think about dust and dirt that could get into the headlight!
If you don’t want to drive a car, connect the battery charger (under the hood terminals) and leave the light on for up to one hour. Don’t let the car idle for an hour! If you don’t have an appropriate battery power supply – drive it, your engine will thank you later.
If condensed water remains in the headlight after the drying method, it will be necessary to remove it according to the repair instructions and then dry it with hot air, continuing until the condensation has evaporated completely.
The headlamp should be dried if necessary by opening the service cover, turn signal module, or control unit openings. Continue to apply hot air for an extra few minutes after the visible condensation has disappeared to verify that all residual moisture has been expelled from the headlight. The hair drier will be enough for this job.
If you are using the industrial hot air blower, set the temperature of the hot air to 120-160 °F to avoid burning the headlight. In any scenario, a temperature of 180 degrees Fahrenheit must not be exceeded.
Repair The Headlight Seal (Gasket)
If the customer agreed to replace the headlights, for me this is the easiest solution. But not so for the owner’s wallet, especially when the new headlights cost more than half of the BMW’s market value. The E90 with adaptive headlights, for example.
If we agree to go the “repair” route, I use the service of the local company that specialized in headlight repairs. So the cost for sealing both headlights is about $500, depending on the model.
If you decide to go the DIY route, I can’t help you much, since I never did it right. I’ve tried a few times but never had enough time to do it properly. All I can tell you is that sealing without dismantling the headlight doesn’t work.
On my cars, I had this problem only once with E90 LCI. To take care of the problem, I just drilled a few holes on the rear bulb cover and they stayed dry after. This is not exactly the recommended procedure, but it worked fine for years.
This is a great guide on sealing the F10 headlights properly.
Also check out this guide.