Misted Headlight

[old son]

On of my headlights is misted up. Is there any particular reason this happens and how do I resolve it please?

[Tomcat3]

You have moisture getting into the headlight so first step is to find out why, could be a crack or possibly bulb cover not fitted properly letting moisture in. Once you have fixed that dry the headlight out with a hairdryer then refit bulbs and bulb cover.

[old son]

Thanks, I've checked the bulb covers and they are in place. There are no signs of any cracks in the casing. If it the seal between the casing can I repair with some silicon smeared around the edge of the casing?

Replacements are from £80 and they might have the same problem so it is worth trying to repair.

[Gadgetman]

I had that on some H4 lights I bought for my GS way back in the mists of time.
(It came with non-H lights, so when I came across a pair at a wrecking yard, I bought them, even with defect)

I cut the old sealant away, all around the light, then replaced it with regular white bathroom sealant.
They held together for years, until the car was scrapped for unrelated issues.

[Tomcat3]

If there are no obvious signs then I would do as you suggest and run sealent around the shell and glass join and go from there.

[cancunia]

I had a similar problem on my M59, there were no cracks or leaks in the unit. It turned out to be bad air circulation due to the vents at the back of the unit. I fixed it by taking the internal filter out of the vent. I've no real idea why it only happened on one side, but allowing air to flow freely in through the vent fixed the problem.