Foggy windshield problem on a sunny day when no one else has a foggy one


I got off work at 4:30 pm the other day, and came out to my new (for me) 2009 car, and the front windshield was foggy. No other windows were foggy in my car, and no windows were foggy on any one of the 50 cars in the parking lot, b/c I checked every one as a slowly cruised around the parking lot before I left for home.

I’m 55 yrs old, and have never had a car do this on a sunny, warm day, in late afternoon, with relatively low humidity in the outside air. The windows were rolled up, yet that should not have been the main source of the problem. The windshield was not a little foggy, it was completely fogged up.

It had also been foggy that morning, but so were the other windows, b/c it was a cool, clear morning, and at 7:00 am on a morning like that, it is expected to have some window fog…but not at 4:30 pm after it’s been sunny all day, and become warm!

What could cause this?..a windshield that is not sealed properly, or what? I did use the defroster that morning, and it worked fine, btw.

Did you turn the heater on?  If so did you get a sweet smell?  Could be your heater core has a leak.  Do you have damp carpet and or sunroof, or is the heater turned on to recirculate?  

One time I had parked over a damp spot in a parking garage.

You have some type of moisture trapped in your vehicle. See if you can locate the source or have a good mechanic find it for you.

In winter months, there is lots of humidity from the passengers in a car. Make sure you run your car with the AC on before it’s parked.

“Make sure you run your car with the AC on before it’s parked.” While it may seem counter intuitive, it is good advice.

Missileman, I think ur answer is the most practical so far, b/c I didn’t do anything different than I’ve done with any car I’ve owned in the last 40 yrs, and this is the first time I’ve had this problem, with only the windshield foggy, after sitting for hrs in the sun on a sunny, low humidty day (high of about 58 or so outside, that afternoon).
There was no sweet smell, no signs of any leaks on the carpet (or around sunroof), the ground was dry under the car where I parked, there were no passengers in the car at any time that day, and there have been thousands of times I have used a car w/o running the AC before I parked it, and this has never happened before, so I don’t think that is the main cause either.
I think there may be moisture trapped in the vicinity of the windshield, b/c of something being wrong, or I doubt if this would be happening. Again, the only fog is on the windshield (and it was completely fogged up), none of the other windows had any fog, and no other car in the entire crowded parking lot had any fog on any window or windshield. Something is wrong with my car, in the windshield area, this is not operator error or a coincidence.
Can a poorly sealed windshield cause this problem; any windshield “experts” out there?
Thanks to all who responded!

If, when you turn on the defroster, the problem quickly gets worse, it’s the heater core leaking or the air conditioner drain is plugged up, allowing water to collect in the heater box… This saturated air then condenses on the windshield…