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Condensation in Forester Headlights

I have a Subaru Forester 2006. This year, noticed condensation in driver’s side headlight after a heavy rain. Not too long after, the headlight blew. (My headlights have been blowing at a frightening rate, but that might be a different thread for another time.). We changed the light and did our best to dry out the inside of the housing. We also checked for leaks by blowing air into the housing, with no luck at finding anything obvious. We put a little flashing on the inside, thinking there might be a problem with the rubber gasket.

Next rain, same problem. We also noticed in a parking lot another Forester, similar vintage, with condensation in both of its headlights.

Is this a known problem…and is there a suggested solution? Thank you!

You need a new headlight assy, one that doesn’t leak. This is not a problem unique to Foresters or Subarus.

Look on the headlight pod for a small bent rubber hose. Moisture is suppose to escape from the pod thru that hose.

Remove the hose and check it for a restriction. Sometimes spiders will lay egg sacs in those hoses preventing the moisture from escaping.


Two well placed holes drilled in the opaque rear shell have solved the problem of moisture on many cars for me. One at the bottom to allow for draining and one at the top for vapor to escape. I am not familiar with the light housings on that car but on quite a few that crossed my path a 1/8" bit and a few minutes time took care of the problem.

Good ideas above. I’ll add that a friend of mine with the same problem takes her hand-held electric hair dryer out to the car and gently heats the headlight ass’y to drive the moisture out. She says once she gets it out, it takes quite a while before it becomes a problem again.

If you decide to change the lighting units yourself, post back and we’ll offer some suggestions. I’ve changed headlight units on modern cars, and some tips might make it easier.

If you decide to have it done, try a reputable body shop rather than a dealer. A dealer will charge you a fortune for this. Aftermarket units will be perhaps half the price of dealer units (or less), and dealer labor rates are often far higher as well.

I’ve had some luck drilling holes as well. One small one at the bottom and a small one at the top of the lense - which enables the moisture to rise and escape when a hair dryer was used. Use a small drill and drill at an upward angle (to prevent rain from seeping in).

Although, as others have noted, look for vent blockage (as Tester suggested) or look for a replacement unit. has them for reasonable prices.

Any moisture on the bulbs will cause them to fail. Also, when installing them don’t touch the bulbs with your skin. The oils from your skin will cause the bulb to fail. Either use rubber gloves or paper towel to install the new bulbs.

Good point by @knfenimore Modern halogen headlight bulbs are not glass - they are quartz which will rapidly fail when heated if contaminated with hand oils. If you accidentally touch them just clean them off with alcohol on a paper towel.

Both glass and fused quartz are silicone dioxide (SiO2). Fused quartz contains far fewer impurities and is thus much stronger than glass, and is actually able to withstand much higher temperatures, which is why it’s used in quartz-halogen bulbs… to allow the filament to be burned hotter without bulb failure and produce a brighter, whiter light. The filaments in both are tungsten fibers.

The bulb can, however, devitrify (become crystalline) when contaminated with certain contaminants.

Those of a more technical bent might be interested to read the attached technical paper from Sylvania on quartz halogen bulbs.

I do, however, have one minor clarification. Their technical paper lists fused quartz as being the “strongest of the glasses”, but there is another that’s even purer and stronger called “fused silica”. I suspect they’re not categorizing it as a “glass” because it’s not generally blown and worked like a glass, but it is used as a lens in extreme applications. It also is virtually transparent to UV, which regular glass is not. Said differently, it’s transmission curve is different than glass.

Enjoy the technical paper.

“Both glass and fused quartz are silicone dioxide (SiO2).”

Since you are obviously technically literate, I assume you know the difference between silicone and silicon.

LOL, I do. Nice catch. I make that mistak often.

Using a term like “glass” is akin to saying something is made of “metal”.

Even something like “Fused silica” has various grades associated with it much like something said to be made from “aluminum”.

People tend to lump all sorts of materials under the term “glass”. For example- borosilicate, 8337, fused silica, sapphire and MgF2 are often all referred to as “glass” windows/envelopes…

Well, yeah. if you want to get technical about it, but I think for the purposes of this discussion the term glass will suffice for a typical, ordinary, non halogen light bulb.

It does, as long as one understands that fused quartz bulbs are susceptible to damage from surface contamination, whereas the old sealed-beam lamps were not.

@insightful Yes, San Francisco had Silicon Valley while Los Angeles (Hollywood) has Silicone Valley.

The best way to remember…thanks, Doc.

I agree, it’s a great way to remember. Thanks doc. {:smiley: