Quick googling, I found forums saying to put the headlight in the oven at around 250 until condensation evaporates, and the glue around the edge will reform. Is this safe? Is there a better way to remove condensation and prevent it in the future?
For reference, I have a 2dr '08 civic coupe.
You can remove the bulb and put a couple desiccants into the assembly until it dries out. You will want to inspect the housing for cracks and any breaks in the seal. You can use silicone sealant to fix the leak.
If it is still under warranty, I would try having them replace it first.
I guess the biggest (and most helpful) part of removing the headlight assembly to bake it would be the fact that you can inspect the breather/venting ports at the same time.
I think baking the assembly at 250 is a little aggressive since that's the temperature most of us run the assembly at for 10-15 minutes when we are softening the glue for housing disassembly.
Here's what I would do if it were my car:
Remove the headlight assembly per service manual instructions.
Remove the bulbs and any harness parts/brackets that are easy to take off of the housing. Put the headlight bulbs in something that will keep them from getting dirty/smudged/greasy.
Inspect the housing. If there are no obvious cracks or breaches move on to the breathing/venting ports... they will have rubber tubes attached to them. You can easily remove the tubes for inspection and clearing. Used compressed air to blow out the rubber tubes OFF OF THE HOUSING. Do not blow air into the housing as you stand a good chance of getting debris inside the chamber that you may never get back out without completely baking and disassembling the housing. If you can see an obstruction in the housing port for any vent then try to carefully suck it out of the port with a small vacuum, solder sucker or similar device.
Bake the moisture out of the housing. With the bulbs out and the vent tubes removed you have a good setup for water vapor to escape during baking. Now place your headlight assembly into a preheated oven at somewhere between 120 and 180 degrees. This is warm enough that the housing will get hot and evaporate the moisture without making the lens sealer too soft. Probably (and this is a guess) no more than 25 minutes at this temperature... keep an eye on the points where it contacts your oven grill just to make sure. I don't think those temperatures are high enough to jeopardize the housing integrity at all though.
Reassemble the housing to the state it was (though cleaner I'm sure) with all tubes and bulbs re-installed.
Re-install on the vehicle and take notice of any areas where water could have flooded your housing... this is where you will be watching in coming weeks.
Hold your breath and hope it was just a one time thing.
NOTE: This happened several times in my Odyssey tails and I actually found tiny cracks in the front housing that would have not looked very good with sealer in them so I replaced the tail lenses.
I bought a second hand car in Jan this year and noticed weeks later a build up of condensation in just the front driver side headlight. Quite heavy droplets had formed so i asked around and was told to try removing the bulb access caps and with a hair dryer blow warm air into the headlight unit until it dried out. Yes it did the trick and i thought that would be the end of it but low and behold a week later and the condensation was back. Anyway im now thinking of taking the car to a dealers to have the whole unit removed to check for cracks or a broken seal somewhere. BUT today i solved the problem with results in just a few hours. I simply removed a couple of the large bulb access caps to allow air to access and moisture to escape. Maybe there wasnt enough ventilation for that unit and with the heat created by the lights moisture would start to build because it could not escape quick enough. What im saying is try it for yourself as it may solve your condensation problem too.
