Hello, I have started to experience this issue for the last 4-5 weeks. Around 6 pm when I’m sitting at traffic or car just sits my back window fogs up on the inside. What could it be? I have some stuff in the truck but it’s mostly just random things, boxes and so on. I do carry a duffle bag with t-shirts and so on. But I usually take it home with me..

 

Your back window fogs up for the same reason as your windshield fogs up - to much humidity inside the car. Two ways to combat this 1. Turn on the rear window defogger, 2. Regulate for HVAC system by having the air conditioner working a little harder. The auto setting does a good job regulating heat and humidity levels. You could also have something wrong with vent doors where they are not opening or closing when required.

 

Sounds basic, but have you tried to clean your windows on the inside? My windows were doing this a lot, and it only has 2500 miles on it, and I keep it super clean. However, I learned that a new car outgasses a lot from the glues and materials used in construction (which is what new car smell is). Once I cleaned the inside, it has been super clear, and almost never fogs except when I would expect it to do so.

 

Yes, it seems better now. I cleaned with Vinegar solution. The other thing that I thought of it might be tinting film.

 

You hit that one right on the head. Good diagnosis!