Condensation is very annoying especially when you have to take the headlight on/off the car frequently to fix the issue that keeps coming back. This How To deals with condensation related to physical water leak due to cracks, bad sealing job, improper seal material, and water ingression from loose/bad bulb sockets.
Condensation in the headlight after hard rain or driving thru water ways on rain storm that resulted in water droplets inside the surface of the outer headlight lens are almost due bad seal. This condensation will cover most of the surface area and would look like raining inside the headlight. Condensation that looks like film or fogging can be caused due to moisture/small water that find its way in or a matter of heat transfer issue which is not very easy to fix. If you get this fogging due to natural convection process inside the headlight, the solution can be tricky and sometimes can't be cured due to law of physics. This How To doesn't deal with this issue, but it would help to eliminate to pin point where water/moisture might coming in.
There are several ways to test if the seal is good. Some put the headlights in the shower and see if the water is in inside. Some were adding more sealant to prevent it from happening. Some put them in the car and go thru the car wash. On Permaseal headllight where (sometimes) the edges were magled it is very hard to get a good seal around that area. On Headlights that has been damaged/repaired, there are big chances that the crack is propagating and more prone for water to get it. But the one thing still remain unknown is the exact location of the leak.
There are few ways to detect leak. You either can push air inside the headlight ( pressurized it ) or pull air from in ( Vacuumed). I chosed to pressurized the headlight, because other thing that I can use with Air Compressor such as painting and other cleaning tasks. The idea to check leak by pressuring the enclosure is nothing new, just like when you had pin holes on your tires and you check where it is by dunking the pressurized tire in the water tank and look for the bubble to show. I'm not using water tank to do this, instead I'm using kitchen/hand soap that you can from grocery store. The kind that when you pump, it produces foamy bubles. The draw back about this method is that you need to be sure that the air going in the headlight is clean and dry.
Disclaimer: If you do this test, do it on your risk. I'm not responsible to any damages/injuries that may occur. Use safety glasses, gloves, and any other safety devices to protect you from any injuries. Safety first.
What you need:
AND Compressed air with drying system.
The air stage dryer system is as the following.
Stage 1: Air from compressor enters to a SpeedAire 5 micron filter which will remove corrosive, moisture, pipe scale, dirt protecting the precision parts in the regulator.
Stage 2: From there, It then goes to SpeedAire air regulator where pressure is regulated as needed.
This SENCO compressor is awesome, it's very quite that I can actually still have conversation and listen to music. I bought a bigger one several days back for the same price, and it was so loud and had too much vibration that I get rid of it the next day.
Stage 3: It would then go to .01 Micron Motor Giuard Coalescing filter where oil aerosols and microscopic particles down to .01 micron absolute are removed from the air.
Stage 4: lastly, air enters the Motor Guard desiccant dryer which is dispersed through a 50 micron element. The element distributes air evenly through the desiccant bed. The desiccant absorbs the water vapor and any other vapors from the air, producing very dry clean air with dew point up to -30 degreeF. The desiccant will turn pink to indicate that it is fully saturated and need to be re-claimed or replaced.
At Stage 4, you are ready to pressurize the headlight. For most headlight, you don't need anything else other than TRS back cap and few butyl tape to plug all the opening, to make sure that you have enough air pressuring inside the headlight. The needle at the end of the desiscant dryer is the smallest I can find and I would just stick the point inside the original hole venting and covered it up with butyl tape.
In the picture below, I actualy made a small hole to insert the needle valve.
Here is bubbles being produced by the foamy soap sprayed aroung the turn signal area when the headlight was pressurized which indicated that it wasn't air tight.
Next, I made a .030" hole on the top and covered it with glue un-evenly. Sprayed some foamy soap water and pressurized it. First there was no buble at 20 psi, when it started to show up at 30 psi. Don't want to increase too much pressure since it might damage the seal. In the beginning I tried with 40 psi before any holes were made, and the headlight seam was OK, but the back dust cap popped.
We don't want too much pressure inside the headlight. Every headlight is different, so the way I can tell that I have enough pressure inside is by looking at the dust boot cover ( from TRS with different sizes). If they start to pop, then you probably had enough and don't want to go more.
Another common area that is prone for leaking is the turn signal seam. This time it was all good.
Here is on the CRV headlight around the seams and covered edges. No big bubbles means air tight.
Here is around repaired area.
The nice thing about this method is that you can test small section and clean and move on. This way, there is no mess or dripping water here and there and you can do this test ( assuming you have the air drying system already) in 10 minutes. If it shows bubbles, wipe it clean, mark the location then you can fix it by adding extra butyl or silicone to fix the leak.
Once you fix any leak paths and waited for the sealant to cure, wipe the headlight clean and run shop vac for 5 minutes to remove any moisture residue OR turn all the bulbs on for 20-30 minutes to vaporize all micro moistures.
An air tight seal on headlight doens't mean that the headlight is fogging proof. Like I mentioned in the beginining, the thin film fogging issue will not be identified and fixed using this method. At best, it will help since you eliminate the variable of bad seal that can introduce moisture/water inside the headlight. At least now you know that you have a good seal, that the little moisture that produces fogging come from somewhere else
Having too much sealant is also not a good thing IMHO, especially if you have a very thin wall housing. The more the sealant, the more the wall needs to "squeeze" that sealant out when you clamp the two halves together. This wall will be somewhat deformed and loosing its original shape that could create an open space if the sealant isn't holding it enough. Koito Sealant is the best so far, you don't need to have a ton in there, just to make sure that you have enough on the area that matters.
On the Part 2, I'm going to discuss about testing the headlight for fogging/thin condensation that is due to non-leaky seal.