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Spots on windshield which show up only if glass fogged or misted

It’s hot and humid here in Illinois. Yesterday my wife was driving early in the morning with the AC on, and the windshield was fogging up on the outside. A pattern of spots showed up, and they persist after the wipers pass over the glass. They don’t show up when the glass is dry, but on washing with windex they show up as the surface approaches dry.

Are these waterspots? Are they something else, like wax or oil? This is a 2010 matrix which we bought used about a month ago, so I don’t know its car-washing-history, but it resided in Florida as a rental, I believe.

Or is there something else possible? Can the glass have gotten “de-laminated” enough to have some internal fogging?

I had the same problem on a 1988 Ford Taurus that I had purchased. The dealer had put the price with some sort of wax on the windshield. Every time the windshield became damp, the price showed up. I think I finally washed the windshield with a vineagar solution to get rid of the problem.

I would agree with Triedaq’s suggestion. Wash half the windshield with vinegar and see if there’s a difference. Let us know the results.

If the vinegar is not strong enough you can try household ammonia. Use it full strength on a soft cloth and avoid any trim or paintwork. Be sure to do this outdoors because the smell is super strong.

I’ve seen this phenomenon too. I suspect it’s from acid rain, but I cannot back that up. I wish I had a SEM in my garage…then I could get to the bottom of the ghost water spots.