Menu

1A Auto Video Library
Our how-to videos have helped repair over 100 million vehicles

Why is There Condensation in My Truck or Car's Headlight?

Share on:
  1. step : No instructions needed (Nov 8 2019 9:52AM)
    • No instructions needed

Condensation in my headlights? Come on. Why is there condensation in my headlights? All right, so earlier technology in automobiles, they had steel beam headlights. Generally speaking, they were sealed glass beams, they had a nice either circle or rectangle beam, and the whole inside of it and everything was completely sealed. It was a halogen bulb of course, and yeah, it generated heat, but that's okay because it was glass. What was going to happen? As technology evolved and styles of vehicles changed, people wanted something more sleek, aerodynamic, better fuel economy, whatever the case may be. Manufacturers began to realize that they needed to create different style headlamps and there's plenty of different style headlamps. And every vehicle has something a little different. Different length, different shape, whatever. To make those out of a sealed beam of glass, something this size, first of all, would be super heavy, where they decided to make it out of plastic, something super light. It's also, of course, much easier for somebody to make out of plastic than it is out of glass. So, the benefits of plastic over glass, generally speaking, would be the fact that it's much lighter, you can make it different shapes, so it can be aerodynamic, it can fit with the shape of your vehicle, but, that of course, led to problems. When you're running halogen bulbs inside of a plastic assembly, the halogen bulb gets very hot, especially if you're running something like a Xenon bulb. Those get much hotter. But anyway, you create heat inside of your plastic lamp assembly. When you have that heat inside your lamp assembly, it was a little bit different when it was glass, the glass didn't want to expand and you didn't have as many chances of it wanting to crack along the seams or get dry and brittle. Plastic, on the other hand, it doesn't like the heat that much. It doesn't like to have a whole bunch of heat on the inside, on one side, and cold on the other. So they had to do something else to try to correct that. They needed to evacuate that heat or vent the heat. So, that's when we get on the backside of these headlamp assemblies, and I'm going to show you where the vents are.

Plastic assemblies need to have some sort of venting. They need a way to let that heat out, right? So they created something like this, a lot of them have this little tube, you pull that off, and it'll generally speaking have a hole that goes into the inside portion of the headlamp. These are not completely sealed, they're vented. The reason for that is because air needs to circulate in and out of there. As the hot air accumulates inside here, it needs to start pushing out. It needs someplace to go. If you start plugging up all these vent holes, you're going to have cracked lenses. Sealing it doesn't make any sense. Then you don't have any way of the heat coming out of the lens. You need to have these vents. Almost every plastic assembly is going to have a vent, and that's to let the heat out. And that leads us to condensation.

So, when you have condensation inside of your lens, whether it's because your vent's clogged, or just because the temperature inside the lens didn't match the exterior temperature, maybe it was a little bit warmer out during the day, you were parked in the sun, you had your headlights on for quite a while, it heated up the air inside of this lens, you park your car, go do whatever it is you're doing, you have some dinner and go get some ice cream, whatever it is you do, you come back out and it got a little bit colder out. The ambient air temperature is a little bit chillier. But the air inside of this lens is still nice and warm. And it's humid and everything like that because maybe there was moisture in the air, you went through a carwash, you ran through a puddle, it was just raining outside, whatever the case may be. You have moist, humid, warm air inside this lens. Right? Now, the cold air is just pushing up against this exterior portion of the plastic. Once this plastic starts getting cold from the exterior air, or the ambient air temperature, it's going to start trying to cool down the temperature inside of the lens. When that starts happening, the thin line of air that's along the inside of this lens is going to start cooling down. And as that happens, all those little air molecules or water molecules that are floating around inside the air start getting cold and they want to try to come together. They're like, "Ohh." They get close to whatever it is that's trying to make them cold. And they're going to attach themselves to along this portion of the plastic lens because that's what's trying to make the interior temperature of the air colder. I don't know if you've ever been sitting inside your vehicle on, like, a winter night or winter day. You're in there and you're breathing, you can see your breath, you're fogging up your windows. It's kind of the same thing. The outside portion of the windows is cold, and the inside portion is getting humid from your body, you know, I'm letting off steam probably right now, actually. It's all accumulating inside the cabin of your vehicle. So then you get the steam inside of your vehicle. Same thing happens here. You crack your windows a little bit, you put on your defroster, same thing. You have a vent, it's going to vent out that air, it's going to circulate it, the temperature is going to be able to match what's going on outside much quicker, and you're going to be able to get rid of that condensation that's inside the lens.

Okay, so here's a prime example of what a headlamp would look like with some condensation inside of it. We've all seen it, we've all gotten a little bit worried about it, and maybe even freaked out, but it's nothing to worry about. This is condensation. Next, I'd like to talk to you about a puddle of water inside your lens. That's something you might want to worry about, and I want to show you a couple things to check out on that.

So let's talk about the backside of these lenses and where they could possibly leak a little bit of water. Of course, you have your vent areas. That's one thing to think about, super important. Generally speaking, you should have something over it, maybe like one of those vented caps that will keep water from splashing right up in there. One of those little tubes as you saw on one of the other lenses, that goes down, it's going to help keep water from splashing in. This right here is a kind of poor design and it could be a great cause of why there would be so much water inside this lens. Another thing you need to think about is you have the areas where your bulbs are supposed to go in, these caps, generally speaking, should have a rubber seal of some sort. And this is super important. This one looks really good, right, while it's on the cap. Let's talk about it though. You take that, you give it a little stretch, and if you can see right here where my finger is, this is not in great condition at all. Moisture can work its way right inside here, and it's going to fill up that lens, easy-peasy.

All right, so let's say you're driving down the road, and a rock comes flying up and bonks your headlight. Bonk. Well, that's going to cause an issue. You're driving down the road continuing on, it starts to rain or somehow water's splashing around, where's the water going to get in? Right about here.

If you have a little bit of condensation inside your headlamp like this, it's all natural. This is what's bound to happen once in a while. There isn't anything that you can do about it. Seal everything as much as you want, you're still going to have issues. If you have an issue that looks like this, well, then you've got real problems. This is not normal. And in which case you either want to try to seal this or in my case, I would just go to 1aauuto.com, get myself a brand new headlamp assembly, and down the road we go.

Tools needed for replacement:

    1A - No Tools Needed

  • No Tools Needed


How To Check Your Brakes & Perform Brake Job

How To Check Your Brakes & Perform Brake Job

Welcome to brakes 101! Learn how disc style brakes work, how to check yours for problems, and how to replace rotors and pads if they need it!

Search Videos
Go To Top


Same Day Shipping

Orders ship same day when ordered by 2pm ET. Need your part faster? Choose expedited shipping at checkout.


Guaranteed To Fit

Providing you the highest quality, direct fit replacement auto parts enforced to the strictest product standards.


USA Customer Support

Exceeding customers' expectations every day, our team of passionate auto enthusiasts are here to help.


Instructional Video Library

Thousands of how-to auto repair videos specific to year, make and model guide you step-by-step through your repair.

Loading...