Dear Car Talk:
Please settle yet another marital dispute. When cleaning the windshield at the filling station, one of us always likes to give the headlamps a scrubbing; the other thinks that doing so puts tiny scratches on the plastic lens, and over the years this will lead to light scattering and reduced visibility. Is it OK to routinely clean the lenses in this manner, or should they be cleaned only under running water, with the scrubbing saved for emergencies?
I'm having trouble figuring out which position each of you is taking. I'm guessing you're the headlight scrubber, Ronald. But I know if I showed an interest in cleaning anything, my wife would be thrilled.
Anyway, now most headlight covers are made of polycarbonate plastic and are covered with a clear-coat sealant of some kind. And over time, that sealer wears off, and the plastic gets yellowed and dulled. The biggest culprit is ultraviolet light from the sun, but road grit and the heat from the headlamps play a role, too.
Overly rough scrubbing of the plastic or using an abrasive cleanser certainly can scratch them up, too. But mostly, these lenses die of natural causes: sun and heat.
When the lenses get cloudy and yellow, your best bet is to take the car to a shop, where they'll use professional tools and special chemicals to buff out the yellowed plastic and -- in some cases -- seal it again. It won't last as long as the original coating on the lens, but it'll at least help for a while. There are do-it-yourself products, but those are even shorter-lasting, in our experience.
And in the meantime, you're free to clean the lenses to your heart's content. But I never would suggest scrubbing them; I'd clean them with a squeegee, like the one you use for your windshield at the gas station.
Wipe them with the wet sponge (with 50,000 windshields' worth of dirt, since the gas station hasn't changed that water since the Carter administration), and then gently clear them off with the rubber blade on the other side. Or wipe them with a clean, soft cloth. Or get your own squeegee and use mild soap and water -- and avoid the prehistoric mud and potentially abrasive grit in the water at the gas station.
And if this interest in cleaning things persists, Ronald, your wife wrote to me and asked me to suggest some dishes.