How I tackled headlight condensation
02-18-2019, 12:10 PM
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How I tackled headlight condensation
I recently encountered an issue with moisture (haze) developing in the drivers side headlight of my car. Of course, the car is just out of warranty, but that's a moot point - several years ago I installed a Morimoto HID kit to replace the weak halogen bulbs so I know and understand why the dealer would not touch it if I asked. Now, before the HID police show up, this kit has been in place for several years with zero issues and the entry point at the access cap is sealed with a tight-fitting grommet and flexible sealant at the edges and wire entry point. Garden hose direct spray on the cap/seal will not penetrate water into the light assembly.Here's what the headlight looked like at the peak of the condensate formation.
This lengthy and meandering post is about what I did to address the moisture. If you go this route, your results may vary, so keep that in mind. This is just to give info about my assumptions and methodology. If your car is under warranty then I think that's the first path, but after looking at a lot of posts, it seems in many cases MB either says this is normal, throws some dessicant bags into the light, or installs super-special vented access caps before agreeing to replace. For me, since replacement is my last option, I didn't have much to lose by some experimentation. Here's a past thread from another member that had a lot of discussion on the topic of headlight hazing and condensation:https://mbworld.org/forums/w212-amg/...yone-else.html
One important take-away from this thread was TSB L182.10-P-051769 "Lamp Unit Fogged/Droplets Forming".
In that TSB there is mention about the headlights being an open system (meaning vented to outside of the unit) utilizing vents with pressure compensating membranes. So basically, the internal pressure either raises such as when engine/headlights are on or in direct sun (heating), or lowers with lights off or in shade, night, etc (cooling). The vents are designed to allow the internal pressure and temperature to equalize to ambient temps. All this assumes that the headlight unit itself is sealed properly, so that was the first step. I very carefully went over the lens, the perimeter sealing, the access caps and the body of the unit, with both water and compressed air and found no defects. So I looked at why condensation occurs. Here is my hypothesis and course of action, often incorrect but always enthusiastic.
Moisture was present inside the headlight in the form of condensation. The haze occurred without any application of outside water source, such as rain, car wash, etc. - it showed up while the car was driven on dry days and parked inside my garage. Note that the MB unit is pretty robustly sealed - my friend Oda112 did an extensive headlight repair and found that the lens is sealed with permaseal material, not a regular butyl sealant. Dang near impossible to break loose in an oven, he had to break out the dremel. https://mbworld.org/forums/e-class-w...gunther-2.html
Generally, condensation forms when moisture in the air turns from a gas (vapor) to a liquid (haze/droplets). This happens as the air cools. Warm(er) humid air inside the headlights was condensing against the lenses, which were exposed to cooler air. Even with the headlights off, remember that there is a big heat producing engine right behind them - everything around it gets heated up, including the headlights and the air inside of them. There's nothing I can do about the heat, air moisture, ambient temps, etc. but there were 2 things I could do about the headlight. First was to check for any cracks, direct openings, or defects - that yielded no issues, everything looked good. Second was to think about air circulation (or the lack of it). Ventilation can reduce or elimination condensation, depending upon how much ventilation there is.
First thing I did as an extreme measure was to remove the parking light bulb access cap (also called a housing cover) entirely, just leaving the access open. By the following morning all condensation was gone and the lens was dry. Makes sense, since internal and external temps were the same, plus air was allowed to circulate freely. Of course, I can't leave the cap off, so it led me to try to find the level of ventilation that would work to keep the light dry. If you look back on that TSB you will see that one solution that MB has come up with is installation of housing covers with pressure sensitive membranes after the housing interior has been allowed to dry. That's important, otherwise I think that it will take much longer (maybe weeks) to eventually get a balance between inside and outside moisture levels after new vents are installed. That TSB info aligned with what I wanted to do for less cost than an MB cover. It also told me that MB is aware of possible failures in the original vents. Next step was to install a 1/8" plastic vent tube into the parking access cap. I chose the parking light access cap as it's easy to get to, plus it looked like the condensation was a bit heavier on the parking light than the headlight area. I added a bit of fiber pad in the end of the tube to act as a dust filter.
I left that in place for a couple of days and found that the condensation returned, but to a lesser amount. So that told me that the new vent reduced the moisture, there just maybe wasn't enough of a vent yet.
I poked around the internet and found what looked like proper membrane-type headlight vents from retrofitsource.com, which is where my HID kit came from. So I bought a couple for about $5 and installed one into the parking light access cap. They are nicely made and gasketed as well.
Here's what the inside looks like, it's not just a direct opening.
Vent installed into the former 1/8" tube location, enlarged to a 1/2" hole.
Cap back in place.
This step was repeated on the access cap for the main headlight bulb. I now had two new vents added to the headlight. Since it's a shared airspace I thought it was reasonable to install two vents to allow air to hopefully cycle a bit from vent to vent.
Again, I let a couple of days go by. During those days the car was driven in warm to cool weather and in fog.
So far, so good, no condensation. For 5 bucks and a little work, any reduction would have been great, so I'm really pleased with the results so far.
Note - the weather did not change drastically during all this, no sudden drop in humidity, etc.
I'm cautiously optimistic but will see what happens as more time goes on. It's not gone through any car wash so that will be another test. There's so many variables on different cars that I'm not saying if you do this it will work, but maybe at least worth a try. If it doesn't work, the vent holes are super simple to plug back up or just left in place with the vents.
Last edited by Mud; 02-03-2020 at 09:52 PM.
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02-18-2019, 12:25 PM
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Nicely done sir! and great writeup.
02-18-2019, 01:46 PM
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Very nicely written! I'm sure it's going to be a valuable resource on this forum, especially as these cars age. I'll have to look at the old headlight units I used for learning purposes and see how those vents work. I didn't even know they existed. Do you think the membranes on them fail or maybe just become clogged by dirt&water?
Last edited by Oda112; 02-18-2019 at 02:06 PM.
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02-18-2019, 01:52 PM
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Well done Mud
02-18-2019, 02:39 PM
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Thanks gents, I'm retired so it gives me extra time to mull the fate of the world, or condensation in headlights, whichever comes first 
Oda, my guess is that the oem vents become clogged with a combination of dust, acids in the air or maybe also from surrounding component off-gassing. Since the oem vent description includes mention of a permeable membrane then there is a film barrier that breathes. You know how even a maintained engine compartment gets a dust layer between cleanings - it's not a far stretch to think that the small membrane can eventually clog and become ineffective. MB addresses the vent issue in that TSB but I noticed that their fixes don't include a blast of air into those vents and I can see why. Even low pressure air would probably wreck the membrane. I'm surprised that they don't offer replacement oem vents but then I'm not sure how the oem vents are secured in place. Plus if it's MB then I'm sure they would be a small fortune lol.
I'd be very interested to hear any results from your closer investigation into the oem vents. I had almost sent you an email to ask if you had a set to look at, but decided to first post up my process, and to gauge results. As I had mentioned, my assumption was that the red circled things in the headlight pic were vents, otherwise I can't think of any other reason to have them.
Anyway, I appreciate the input/comments, hope this may be of some help down the road.
I'll surely post a later update(s) - we are supposed to get some rain this week, plus I typically run the car to the dealer (close to me) for a wash every couple of weeks or so. So I think either will be a major test.
Oda, my guess is that the oem vents become clogged with a combination of dust, acids in the air or maybe also from surrounding component off-gassing. Since the oem vent description includes mention of a permeable membrane then there is a film barrier that breathes. You know how even a maintained engine compartment gets a dust layer between cleanings - it's not a far stretch to think that the small membrane can eventually clog and become ineffective. MB addresses the vent issue in that TSB but I noticed that their fixes don't include a blast of air into those vents and I can see why. Even low pressure air would probably wreck the membrane. I'm surprised that they don't offer replacement oem vents but then I'm not sure how the oem vents are secured in place. Plus if it's MB then I'm sure they would be a small fortune lol.
I'd be very interested to hear any results from your closer investigation into the oem vents. I had almost sent you an email to ask if you had a set to look at, but decided to first post up my process, and to gauge results. As I had mentioned, my assumption was that the red circled things in the headlight pic were vents, otherwise I can't think of any other reason to have them.
Anyway, I appreciate the input/comments, hope this may be of some help down the road.
I'll surely post a later update(s) - we are supposed to get some rain this week, plus I typically run the car to the dealer (close to me) for a wash every couple of weeks or so. So I think either will be a major test.
Last edited by Mud; 02-18-2019 at 02:43 PM.
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02-18-2019, 03:22 PM
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Thanks gents, I'm retired so it gives me extra time to mull the fate of the world, or condensation in headlights, whichever comes first
Oda, my guess is that the oem vents become clogged with a combination of dust, acids in the air or maybe also from surrounding component off-gassing. Since the oem vent description includes mention of a permeable membrane then there is a film barrier that breathes. You know how even a maintained engine compartment gets a dust layer between cleanings - it's not a far stretch to think that the small membrane can eventually clog and become ineffective. MB addresses the vent issue in that TSB but I noticed that their fixes don't include a blast of air into those vents and I can see why. Even low pressure air would probably wreck the membrane. I'm surprised that they don't offer replacement oem vents but then I'm not sure how the oem vents are secured in place. Plus if it's MB then I'm sure they would be a small fortune lol.
I'd be very interested to hear any results from your closer investigation into the oem vents. I had almost sent you an email to ask if you had a set to look at, but decided to first post up my process, and to gauge results. As I had mentioned, my assumption was that the red circled things in the headlight pic were vents, otherwise I can't think of any other reason to have them.
Anyway, I appreciate the input/comments, hope this may be of some help down the road.
I'll surely post a later update(s) - we are supposed to get some rain this week, plus I typically run the car to the dealer (close to me) for a wash every couple of weeks or so. So I think either will be a major test.
Oda, my guess is that the oem vents become clogged with a combination of dust, acids in the air or maybe also from surrounding component off-gassing. Since the oem vent description includes mention of a permeable membrane then there is a film barrier that breathes. You know how even a maintained engine compartment gets a dust layer between cleanings - it's not a far stretch to think that the small membrane can eventually clog and become ineffective. MB addresses the vent issue in that TSB but I noticed that their fixes don't include a blast of air into those vents and I can see why. Even low pressure air would probably wreck the membrane. I'm surprised that they don't offer replacement oem vents but then I'm not sure how the oem vents are secured in place. Plus if it's MB then I'm sure they would be a small fortune lol.
I'd be very interested to hear any results from your closer investigation into the oem vents. I had almost sent you an email to ask if you had a set to look at, but decided to first post up my process, and to gauge results. As I had mentioned, my assumption was that the red circled things in the headlight pic were vents, otherwise I can't think of any other reason to have them.
Anyway, I appreciate the input/comments, hope this may be of some help down the road.
I'll surely post a later update(s) - we are supposed to get some rain this week, plus I typically run the car to the dealer (close to me) for a wash every couple of weeks or so. So I think either will be a major test.
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02-18-2019, 09:17 PM
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I went ahead and ordered a second set of 2 vents to have around in case the passenger side headlight shows condensation. Cheap enough to keep in my MB parts bin.
I share your sentiment - half my time is spent looking for what I stored away, the other half is looking for what I misplaced.....
I share your sentiment - half my time is spent looking for what I stored away, the other half is looking for what I misplaced.....
Last edited by Mud; 02-18-2019 at 09:21 PM.
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Mud (02-19-2019)
02-21-2019, 06:32 PM
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I thought I'd post an update.
Today the car was driven in rain, headlights on. I checked upon return and there was a tiny amount of haze ( no droplets) in the lower inside corner of the parking light, about 1/4" width by 1/2" length. It was gone within an hour. I think this is ok, I can live with it if this is all there was.
Today the car was driven in rain, headlights on. I checked upon return and there was a tiny amount of haze ( no droplets) in the lower inside corner of the parking light, about 1/4" width by 1/2" length. It was gone within an hour. I think this is ok, I can live with it if this is all there was.
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Mud (02-22-2019)
02-22-2019, 11:37 PM
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Thanks for trying this solution, Mud. And thanks for taking the time to write it up.
I hate headlight condensation, and thankfully my E550 doesn't have it (yet). Your investigation seems reasonable to me, as does the solution. Please keep us updated.
I hate headlight condensation, and thankfully my E550 doesn't have it (yet). Your investigation seems reasonable to me, as does the solution. Please keep us updated.
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Mud (02-23-2019)
02-27-2019, 05:09 PM
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I'll post this as sort of a final update unless something changes significantly.
Last few days the car's been driven in light and hard rain at highway speeds. Humidity here in TX has come up, temps 50's at night, warming slightly during the day. I'm thinking perfect conditions for developing haze.
I'm pleased to say that there has been zero condensation/haze observed inside the light.
This also appears to verify that the assembly itself is watertight - none of these vents would help if water was coming in somewhere.
Edit - at the risk of beating this topic to death, the car also went through the dealer carwash this afternoon with no headlight issues.
Last few days the car's been driven in light and hard rain at highway speeds. Humidity here in TX has come up, temps 50's at night, warming slightly during the day. I'm thinking perfect conditions for developing haze.
I'm pleased to say that there has been zero condensation/haze observed inside the light.
This also appears to verify that the assembly itself is watertight - none of these vents would help if water was coming in somewhere.
Edit - at the risk of beating this topic to death, the car also went through the dealer carwash this afternoon with no headlight issues.
Last edited by Mud; 03-01-2019 at 09:06 PM.
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03-01-2019, 12:56 AM
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Here is a direct link on the web site in case anyone has difficulty navigating it. https://www.theretrofitsource.com/bo...ther-vent.html
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Mud (03-01-2019)
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Mud (04-24-2019)
03-24-2020, 07:33 PM
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What about Purging with Nitrogen, then sealing the unit totally. Purging with Nitrogen will remove all moisture. Having a sealed unit no matter how hot it gets ( I'm not a scientist) with Nitrogen inside, means no moisture and nothing to expand substantially to cause any issues. The vent is not there for heat, its there for the expansion of water vapor. There is no way to keep out water vapor with any simple membrane. Just a thought. Your solution is great except the volume of air has moisture content in it. How much is open for discussion. Nitrogen is used in tires(Aircraft) and HVAC systems to purge out moisture and oxygen etc.
03-25-2020, 09:17 PM
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What about Purging with Nitrogen, then sealing the unit totally. Purging with Nitrogen will remove all moisture. Having a sealed unit no matter how hot it gets ( I'm not a scientist) with Nitrogen inside, means no moisture and nothing to expand substantially to cause any issues. The vent is not there for heat, its there for the expansion of water vapor. There is no way to keep out water vapor with any simple membrane. Just a thought. Your solution is great except the volume of air has moisture content in it. How much is open for discussion. Nitrogen is used in tires(Aircraft) and HVAC systems to purge out moisture and oxygen etc.
I think that as long as the moisture inside equals the moisture outside there's not a condensation issue?
What I can say is that since posting this vent fix there has been zero, zilch condensation that has returned in the headlights. Not even a haze. This is through all sorts of weather, temperatures, dealer washes etc.
As mentioned, my own unscientific theory and now longer term observation is that as long as the airflow/temp is allowed to equalize by venting, condensation would be avoided. So far so good.
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pierrejoliat (12-17-2020)
12-16-2020, 06:36 PM
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I suppose that may be possible in theory as long as you can seal off the access ports but then you'd have to re-seal any time you changed a bulb.
I think that as long as the moisture inside equals the moisture outside there's not a condensation issue?
What I can say is that since posting this vent fix there has been zero, zilch condensation that has returned in the headlights. Not even a haze. This is through all sorts of weather, temperatures, dealer washes etc.
As mentioned, my own unscientific theory and now longer term observation is that as long as the airflow/temp is allowed to equalize by venting, condensation would be avoided. So far so good.
I think that as long as the moisture inside equals the moisture outside there's not a condensation issue?
What I can say is that since posting this vent fix there has been zero, zilch condensation that has returned in the headlights. Not even a haze. This is through all sorts of weather, temperatures, dealer washes etc.
As mentioned, my own unscientific theory and now longer term observation is that as long as the airflow/temp is allowed to equalize by venting, condensation would be avoided. So far so good.
12-17-2020, 01:42 PM
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Makes me wonder if Mercedes used some type of desiccant in the "membrane" that over time blocks the stock venting, I guess it could be dust, but that would take a some time based on microns of filtration I believe if you were not in particularly dusty conditions.
The membrane would have to work in both directions, absorbing water on the way in and aspirating water on the way out. Interesting dilemma, I wonder if anyone has every actually removed a membrane or examined it for dirt or desiccant?
Either way, great fix!
The membrane would have to work in both directions, absorbing water on the way in and aspirating water on the way out. Interesting dilemma, I wonder if anyone has every actually removed a membrane or examined it for dirt or desiccant?
Either way, great fix!
12-20-2020, 09:33 AM
#21
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Thank you for the write-up. I just started experiencing this issue and your solution seems like it could work.
Do you happen to have a link to the product page of "proper membrane-type headlight vents from retrofitsource.com"?
I searched around the website and couldn't locate it.
Do you happen to have a link to the product page of "proper membrane-type headlight vents from retrofitsource.com"?
I searched around the website and couldn't locate it.
12-20-2020, 11:27 AM
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https://www.theretrofitsource.com/bo...r-B?quantity=1
For the low cost I think these are worth a try. I can't guarantee that they will fix anybody else's problem but in my case they resolved the issue.
For the low cost I think these are worth a try. I can't guarantee that they will fix anybody else's problem but in my case they resolved the issue.
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