Repairing a "milky" plastic headlight cover

[NomoneyNohoney]

My car is away having its MOT at the moment. One of the headlamp lenses had gone 'milky' and was cloudy compared to the other.

I'd read online that you could polish it up or suchlike, but there was another tip I tried : I used a small tube of toothpaste and some paper towels. Put a smear of toothpaste over the lens, let it dry and then polished it off with the paper towels.

Honest to God, absolutely transformative: the lens is as clear as the day it came out of the factory, and I am stunned at how good the results were. Just a little tip in case any of you might have similar problems. Gobsmacked me! (Makes me wonder about using toothpaste on my teeth though...)

[XFool]

...Just to point out - assuming it is not already well understood - that the problem is caused by automatic car washers (and plastic rather than glass lenses, on today's cars).

[bungeejumper]

Whatever you use, you will most likely grind off the UV protection coating on the lens. If there's any left, that is, because it's probably the loss of the UV coating that caused the lamps to cloud up in the first place. Fortunately the lacquer isn't expensive to buy.

For tougher scratches, the trade tends to use cerium oxide, which is usually sold as a glass polishing medium - dammit, it's even used for cutting gemstones! Cost me £9 for a 50 gram tub (like a shoe polish tin), and it went through some deep scratches on SWMBO's headlamp lens in record time. If you're using an electric drill and buffer wheel, they advise you to keep the drill speed low in case the friction overheats the lens.

BJ

[DeepSporran]

It may well be that automatic car washes often cause this problem. However I know from personal experience with a van that never ever went through a car wash that there are other causes. Possibly just the long term effect of UV degradation of the plastic outer surface of the headlamp. lens. My van failed the MOT at 15 years old with this issue. The toothpaste trick helped a bit but I resorted to buying a kit that included an abrasive fluid (which was no more effective than toothpaste) plus a set of 4 wet-and-dry abrasive pads of progressively finer grades of grit. These latter did the trick although it’s a scary process - after using the roughest grade pad the headlamp became completely opaque. After progressing to the finest grade however, there was a transformation. A final going over with the abrasive fluid and things were great.

One caveat though - as Bungeejumper points out, this process removes all traces of the toughened outer surface of the lens and it will turn milky again after some months. The lacquer that came with the kit didn’t seem to be very effective for me. However you normally just need to have a go with toothpaste or the kit’s abrasive fluid this time.

That was my experience anyway. Certainly cheaper than fitting new headlamps.

[redsturgeon]

I did my old Honda headlights well over a year ago with a kit and used the UV lacquer included. They are still clear.

John

[Dicky99]

Ed China did this multi stage process on one of the Wheeler Dealer cars though my memory fails me on which one. Maybe the Porsche Boxter??

[DrFfybes]

Halfords, Eurospares, etc sell headlight renovation kits for about a tenner.

Paul

[NomoneyNohoney]

I'm still happy with kitchen tissues and 50p ASDA value toothpaste! Car passed its MOT so if it needs it, I can do it again next year.