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

My sister parks in her driveway and never cracks her windows. I once asked why and she said that you needed an opening as big as your fist to do any good, which did not make any sense to me, and the other day she told me that cracking the windows actually makes it hotter, so I asked if leaving the oven door open a crack made it hotter and she said that it was different.

Good point.

This does not have anything to do with theft prevention, even though her vehicle is pretty new, many times she has told me that her vehicle is unlocked, and her children leave their bikes in front of the garage overnight, and for months on end.

What do you guys say? I did a quick search and one argument is that cracking the windows would enable temperatures inside and outside to equalize faster, but AC does not do any good unless it is running!

This is the only thing that I found of any use and I would not ever use this or anything else to argue with my sister... or any other woman.

When Should You Open Your Car Windows? An Experiment – Uncertain Principles

The important part: http://scienceblogs.com/principles/w...p_with_fit.jpg

They parked two almost identical cars in the sun and recorded those results.

First we need to know if she is one of those rare individuals that responds to facts. Otherwise, you need to figure out which- if any- emotional buttons to push to effect change.

After the car getting parket for a while in an open space during hot days, my dad always says that it's better to leave it open for a while to the trapped hotter air to escape before getting in.

I wish they had let that experiment run for another 30 minutes.

As for theft: it's darn near impossible unlock a car door with a coat hanger these days with the new lock operator shapes. They use one of those slimmy jimmy bars to break in, which slide into the door between the window and the seal. Thieves could care less whether the window is down or up, unless it is down far enough to stick an arm through.

I have an in/out digital thermometer to measure air intake temp, but by location it also measures the temperature on top of my dash.
It can run off the scale (over 70C) with the windows closed.

When I leave the windows on the tiniest of crack it never runs so high. On the downwind side you can feel the heat escape through the crack.

I have a foam backed silver sunshade that I put over the windscreen when it is sunny. That's even more effective than (just) cracking the window.
I really wonder why so few people use them.
In the winter it keeps the window clean from snow and ice, and maybe just 1 degree warmer than without it; just enough to make it noticeably fog up less on start.

I've actually had an older SGII's plastic warp on top from getting too hot with the windows rolled up (it sat on the top of the dash). With windows open it has never been a problem. I leave them cracked whenever its not going to rain in summer.

Heh. I just want data. I do not plan on discussing this with her.

I have a sunshade and on a previous car, I used one on the back window, too, although I recently had my windows tinted, and that seems to make a huge difference. I have not really used the shade since, but part of that is that Pep Boys grabbed the shade and shoved it in front of the passenger seat and then I asked a girl to fold my shade and she folded it ways that it was never designed to fold, so I should purchase a new one.

My car tends to get dusty here in Arizona, but I think that most of the dust on the dash is actually from the shade.

I've found that leaving windows open is very good at keeping cabin temps down, but that's mainly because it causes it to rain.

What's the functional difference between a parked car and a greenhouse?

A greenhouse allows energy transfer in via radiation (which is absorbed by the contents), but prohibits convective heat loses--the main source of outward enegy transfer.

As if to prove a point, I forgot to put the windshield cover on, windows closed.
It was a stove. 60 Celsius while it was just 22 outside.

To make matters worse the inside of the dash, where the ventilation channels are, gets seeringly hot too; it takes minutes before it cools down to normal levels even at full blast. So my first miles are with the windows full open and the vent at max. After that, entering the highway; close all, ventilator low. A/C on with recirculation if needed (not today).