Moisture inside head lamp casing

My driver side front head light compartment continually has moisture inside of it. My question(s) are how does that happen, and is there a way to stop it without just replacing the entire unit? The head light works okay but figure that this can’t be a good thing.

2002 Kia Sedona Mini Van
6 cylinder
147,000 miles

There is an opinion that this problem is caused due to a headlamp defect such as a crack or seal but I respectfully disagree with that.

In my opinion anyway, it’s caused by lack of venting. Both of my Lincolns (known for lousy lamps anyway) would condense moisture so badly that they looked like the wall of a steam room.
I solved this problem by doing 2 things. One is that I removed a 1/4" diameter plug on the bottom of each lamp and this provided free access to the atmosphere.
Two is that I routed a small nylon air line from each lamp to a T-fitting and then into the air cleaner housing.

The reason for the latter was not moisture removal though. It was to remove extreme heat which was burning the lamp reflectors. The point could be made that whenever the engine was running any moisture along with heat would be removed also but even while sitting none of the lamps ever condensed moisture again even with the plug in the bottom removed. A 1/4" drill would do the same thing, lacking a removeable plug.

Bottom line is that after doing the above there has never been a hint of any condensation in the lamps even on the most humid of days.

There’s a leak somewhere. Once the bulb is installed correctly it becomes a seald unit. A crack or seam glue space will allow the exchange of air getting moisture in.
That moisture isn’t a big problem unless it get on the bulb which will explode.

For one customer of mine who was in a big hurry to get home, I used box tape over the missing front of the lens to keep out the water splash and they made it home without having to repeatedly replace the bulb .

Yours may not be so obvious. Just a stone nick or the seam glue saparating will let in moisture.
Find the hole, seal it, dry it out, and reinstall.

But to find a leak you can’t see will require removing the lamp ( and the bulb ). Fill it with air pressure or water and look for the leak.

My 2000 Blazer had the same problem. I was able to remove the entire headlight assembly. To dry out the interior I used a paper towel fed through a bulb opening to remove as much moisture as possible. I used a hair dryer to evaporate the rest. I sealed the joint between the clear lens and the back of the assembly with a thin layer of silicone sealant.

Ed B,

The lamps on my Lincolns were tested for leaks by immersing them in water. Nothing.
As of right now, and has been the case for some years, the lamps on my Lincolns are wide open exposed to the atmosphere with never a drop of moisture present ever since being exposed.

If being exposed to the atmosphere caused condensation in the lamps then are mine not saturated? They were certainly saturated before the plug removal.

The last 2 days has been extremely humid here with everything being soaked and dripping (including under the hood and my entire covered front porch) but the lamps have remaind bone dry.

If this is a new problem then a leak is the likely cause, if it’s always done it then ok’s solution should work.

You have to remember they sit right out front and are driven into rain, and splash from other cars at highway speeds. (think hurricane force wind) Any little seam or smallest opening of any kind is going to let water in. Not to mention the abuse they get from gravel, etc.

DfromSD is right. Tiny cracks in the seal might not let in the water if you dunk it in a bucket, but if you drive the water at it at 90mph (70mph+20mph wind) while things are vibrating and flexing it’s quite a different story. A fully sealed headlight won’t develop moisture. Once the seal is broken even slightly, you start building up moisture, and it’s time to drill a vent hole.

Look at the back of the headlight and there should be a small rubber tube that allows the headlight to vent to the atmosphere. Remove the rubber tube and look for blockage inside the rubber tube. Something like a spider’s egg sac.


Driving at speed and rainfall is not the issue on my Lincoln lamps. The lamps would accumulate a lot of moisture while the car is parked without even being driven and there has been no rain at all.
It’s due to heat in the lamp assemblies and humidity in the air. The lamps cool and draw humidity in; either at night after the lamps are turned off or as the sun that has been shining on them begins to fade.

Even at highway speeds and with that open 1/4" vent hole no water enters the lamps at all. With the current vent and air line the lamps barely even get warm even after extended operation for several hours whereas before they would not only get hot but actually burn the reflectors orange and black.

I’ve seen this on newer Toyota’s. Not uncommon. Have you asked the dealership if they have any ideas on how to fix it? They probaby have other customoers who have asked this same question, and they may have figured something out how to fix it by now. Ask them to check the tech bulletins. Also, visit your local public library. Many libraries now have a computer service where you can view the repair bulletins for your make and model. I think it is called “AllData” or something like that.

If it were my car, I guess the first thing I’d do would be to heat the headlamp (carefully so as not to make it too hot, just warm it up a bit) with an electric hair dryer. Be aware that an electic hair dryer will ignite gasoline and could explode, so keep it away from all gasoline and other flamables. Hopefully doing so would heat the air inside the unit and cause it to vent. It might just work. It wouldn’t solve the problem forever, but might be a temporary solution. I think most drivers just live with it.

When I was a used car dealer I used to drill small holes at the top of the light (under the hood, out of sight, and under a trim flap if I could). This allowed the steam to escape and the lense would clear out in a day or two.