Cracking the windows in the summer, which lasts six months in Arizona.

[Frank Lee]

Yeeeaaaahhhhh, that's not going to do much in the shade.

[vskid3]

I crack my windows an inch or two when I park at work, leaves it noticeably cooler than leaving them up. My sunshade doesn't fit very well in the super long Prius windshield, so I usually park with the rear facing south as the rear window is smaller and tinted.

[NeilBlanchard]

If it is hotter on the inside than it is outside, then it is better to let some of the hotter air out of the car. In my experience, the inside of the car gets hot even in the winter. In the summer, it gets downright scorching inside any vehicle.

White vehicles are significantly cooler in direct sunlight, than are most other colors. Dark colors are significantly hotter inside, in direct sunlight; because of their lower albedo. White has the highest albedo, so it reflects more of the visible light; similar to the reflective shields for the windshield.

Visible light passes through the glass and warms materials inside the car, and it becomes infrared light, which cannot easily pass back out through the glass.

[Xist]

I do not use my shade much.

Silver is a color, right? How reflective is that?

Also, I recently tinted the windows, which is supposed to be a radiant barrier or something, bits of metal or something:

Our premium product is SunTek HP, this is a metalized film with 99% UV rejection and carries a lifetime guarantee.

[redpoint5]

I have working AC on my cars, so blocking the sun isn't worth the time and effort to me. My guess is the extra energy required of my AC to cool the cabin down from being a few degrees warmer would never be measurable.

Normally I crack the windows open when it's hot out, but now that I think about it, the extra wear and tear on the window actuators might not be worth the effort. I do have a moon roof and often leave that cracked. Perhaps that is enough. If anything wore out due to my effort to cool the car a few degrees, it wouldn't be worth it to me.

[Frank Lee]

the extra wear and tear on the window actuators might not be worth the effort.

Seriously?!?

[Xist]

Well, a car in Arizona with closed windows is a solar oven. I do not know that cracking the windows does much, but people talk about cars reaching 180° in the sun.

[RedDevil]

Left it off this morning as rain was forecast.
Guess what, blue skies and 'the weather will improve during the day'. Improve on what? Additional conga girls?
Gotta put the shade on or I won't be able to sit in my chair without charring my back when I go home...

[Cd]

Texas here.
My sister had a window repair guy tell her that her window shattered due to the trapped heat in the car.

Personal experience has been that I now leave my windows up since my cars ECU gets wet even if i crack the windows just a bit.I had to replace this very expensive part after much frustration trying to find the source of the problems with the car.

[RedDevil]

I wonder about having a small solar panel feed the ventilator so that it cools the car and the in-dash vantilation channels while the key is out. It only needs to do that in the full sun.
Needs a diode in the normal feed line to prevent feedback on the other systems.