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).

I've always kept my windows cracked while my car is in the open sun and I plan to drive it again that day. I haven't measured temperatures, but it does seem to keep it a bit cooler. The inside of a closed car can me much hotter than the ambient temp. thanks to the sun.

I can't tell you how many times I wish I had left the windows cracked. My drivers side A-pillar has plenty of battle scars from me breaking into my own car with a wire hanger because I locked the keys inside. It's so easy to break into my car I don't even lock it anymore.

from 11-2:30pm in 80F+ heat the UG reads itself in the 160F+ operating temps imagine what the inside car temp would be :p

Do you put the shade inside the car ?
It'll work far better when on the outside.

Would it get stolen if you put it on the outside ?
I can't recall anyone saying theirs were stolen
(here we use them in winter to keep the frost / snow off the windows)

I now have a car with fold-out rear windows again - old Jap style , even though it's a 4 door (VW being cheap) - and I like having them open for ventilation unless it's so hot the A/C has to be on.

Yes, it would work better on the outside and create less of a mess, I just do not know how to keep it there! :)

I only recently got my ac fixed, last year was over 100 for over a week, I wasn't doing that again.

What I noticed about the heat from leaving the windows up is that not only did it get hotter, but the interior itself gets heat soaked and continues to radiate heat until it is cooled down.

Is it a bit oversized where you could stick just the edges inside, and then roll the windows up to lock it in place?

Heh. No, but I guess that I can use a cargo strap! :)

In a car with sunroof, it can be left popped-up to leave hot air to get untrapped.

It is a bit oversized so it can fold round the A pillar and be locked by the doors, rather than the windows.
I will add a photo soon. I'm on my tablet now.
(zap)
So here it is:
http://imageshack.us/a/img855/9753/lpty.jpg
As you can see it has 2 flaps, but is just wide enough to get clasped between the door and the A pillar anyway. Makes it more wind resilient.

Front is alu foil, back is thin plastic foam. It is a bit worn from frequent use.
http://imageshack.us/a/img822/4545/l5wv.jpg

Rolls easily, weighs just a couple of ounces.
http://imageshack.us/a/img839/4658/5bjq.jpg
They sell these for a couple of euros in general auto parts stores.

Had it on today, full sun, ambient 25C, windows closed. Temp inside on return was 36 Celsius. Beats cracking the windows imho. :)

Well, ours certainly do not have those flaps, at least I have not seen any, but that certainly would do the job.

Mine will do the job, but it looks a bit funny, which does not stop an Ecomodder, right? :)

https://sphotos-b-dfw.xx.fbcdn.net/h...87716777_n.jpg

https://fbcdn-sphotos-e-a.akamaihd.n...51543727_n.jpg

Curious thing is, the doors do not have frames, the windows roll into the body, so it is a bit of an either-or thing, eh? :)

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

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.

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.

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:

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.

Seriously?!?

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.

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...

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.

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.

I do live in Oregon, and not Hades. If it gets so hot inside a car that it starts to degrade the interior and dashboard, then it would certainly be worth cracking windows or putting up a sun shade. My thought is that it isn't worth the effort if the heat doesn't cause premature failure of these things.

I walked out to my car this afternoon to pop the hood and take a picture of a part. The car had been sitting in the sun all day. It's about 95 degrees. When I opened the door it was similar to opening a hot oven. I could feel the heat difference. The interesting part was when I began to see the heat escape the car as I stood there with the door open. It was like looking at the top of a hot asphalt road. I could see the heat rising out of the interior.

It just made me think of this thread, so I decided to share.

Effort?

I thought the concern was wearing out the power window.

Where in the world is your ECU located where it'll get wet it you leave the window open? Every one I've ever seen is under the hood.

Or you could buy this.

Amazon.com: Solar Powered Car Auto Cool Air Vent Cooler Cooling Fan: Electronics

But customer reviews are not good, and then there's this:

Does it work? Solar Powered Ventilation System - YouTube

My ECU is located in the passenger side kick panel. It's right in front of the door, and only protected by a piece of plastic. If water found a way to drip off the dash, it could easily get to the ECU. I think most car ECU's are located in the passenger compartment. I've never seen one under the hood.

I honestly do not know where my ECU is, but it is good to know that I can never ever ever leave the windows cracked in a Civic if there is the slightest chance of rain.

I wouldn't go that far. I've owned Civics for 7 years and never had any problem. Actually, I've never heard of it being an issue on the Honda forums either. While it sounds vulnerable (and I guess it is) the chances of anything happening are slim. You probably wouldn't want to leave the windows down in a hurricane or anything though.

My SE-R's & xB's ECUs are definitely inside the passenger compartment, Diesel Dave.