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Sat Apr 19, 2025 11:00 pm

I’ve recently noticed an odd white residue in my Bosch H4 headlights; it isn’t fogging or moisture, but a layer almost like a powder electrostaticaly deposited. Streaks and lines. It takes some effort to scrape it off. These are from my 65 but the bay has it as well. Both sets bought from Bus Depot years ago, but residue showed up after recent use. 70 is stored outside, 65 in garage, so weather I no factor. Ideas?

Curvy lines of residue.

Zigzags from 6 to 7 o’clock where a long cotton swab scraped it off.

Hard to see I know.

Sat Apr 19, 2025 11:13 pm

I used to get it in the Cibie ones after a few years, and my Acura's and other cars get it too. All I can tell you is be careful how you go about trying to remove it.

Sun Apr 20, 2025 12:22 am

Ha. I avoid g@@gle so much I didnt think to look it up anywhere but here. Apparently a common problem; denture cleaner seems to to be favorite solution (no pun intended). No answers on what it is, however. I'd assume something baking off/out of the bulb?

For fun, well see if the Bosch, Toyota, Hella or LED units I have fog up fastest or worst. Might be a long experiment...

Sun Apr 20, 2025 4:35 am

I have had good luck with denture cleaner followed by a rinse of distilled water. It can take a while to get all the moisture out of the headlight when you are done. Warming the oven up to 200°F, turning it off, and then letting the residual heat dry them out works.

Sun Apr 20, 2025 7:34 am

It is a combination of oxidized sealant or adhesive from the joint between the glass and reflector....mixed with some oxidized metal from reflector. You can see this on the reflector as well. It usually has a very slight haze on the reflector.

A mixture of classic index with ammonia and about 50% water sloshed around and then rinse with distilled water. I dry with a plastic or metal stick with a lint free wiper on the end.

The ammonia in the index is key because it raises the PH and allows detaching the haze. An acidic produ t like vinegar would also suffice (ph change either way) but ai would not use vinegar with the plating on the reflector. Rinse well.

Ray

Sun Apr 20, 2025 10:17 am

Thanks, all; as this seems to have been happening for years, one hopes the manufacturers would have decided to find different adhesives. Another expense outsourced to consumers I guess. As it noticeably diminishes the bulb's efficacy, some lawyer should do one of those class-action suits I keep getting notices about, saying 'did you ever drive a car? YOU may be a class member!'

We'll all get a check for fifteen cents.

Sun Apr 20, 2025 10:48 am

70bus wrote: Thanks, all; as this seems to have been happening for years, one hopes the manufacturers would have decided to find different adhesives. Another expense outsourced to consumers I guess. As it noticeably diminishes the bulb's efficacy, some lawyer should do one of those class-action suits I keep getting notices about, saying 'did you ever drive a car? YOU may be a class member!'

We'll all get a check for fifteen cents.

All adhesive and sealants do it....modern or old.

The difference that keeps some....if not most.... modern headlamp assemblies from getting this fogging is that most use no adhesives. The headlight assemblies are usually either heat welded plastic or use plastic ultrasonic welding, or snap together and have the sealant/adhesive on an outside joint.

Our old school lamps are mostly metal joined fo glass. Some later builds I have seen are glass joined to glass but still require an adhesive.

Ray