Are there any studies on how much cracking the car windows can help keep the temperature down in a car on a hot day?
That’s so funny, I was just thinking of posting this question.
I kind of answered it myself - I think the minimum temperature you could hope your car to reach is the ambient temperature outside. So, the best scenario for keeping your interior cool is to have the windows all the way down. Simply cracking them will still allow heat transfer but the ambient temperature in the car will surely be greater.
I’m not sure anyone has the gumption to do a scientific study evaluating how many inches your windows have to be lowered to achieve “acceptable” temperature. If so, there would have to be a corrollary study showing how many inches they have to be RAISED to avoid car theft!
My impression was that cracking the windows was not so much to keep the temperature lower, but to prevent a window or windshield from popping out due to increased pressure from the heat buildup. I may be completely wrong, but somewhere back in the dim dark days of long ago, I think I read that.
From personal experience, it makes a significant difference. If I’m required to park in the sun, I’ll leave all four windows cracked 2 to 3 inches, and also pop the sun roof a bit (if the car has one). The car will still be hot, but won’t have that just opened the 500 degree oven feel.
All cars have pressure relief vents, usually a port in the door with a rubber flap over it.
Whew! That would be scary. 
But no, it’s just for heat.
I saw an ad on TV for a little fan to be attached to a cracked-open window. The “test” showed the fan car around 30 degrees cooler, (no word on the outside temp, which is probably the trick.
Venting the windows definitely has some effect, but when it’s miserable outside, too, it’s not much.
I saw that too and was wondering about it. If I can find one at a wal-mart or Bed Bath and Beyond, I’ll get one (unless their really expensive). If I could get my car anywhere near ambient temp, I’d be happy. In fact, anything less then what it normally get’s to would make me quite happy.
I used to have one. They work.
I gotta get another one.
Ask any vet (or doctor) and they’ll tell you cracking the windows doesn’t make THAT much difference. A pet (or child) left in a car on a hot day will die just as quickly with or without the windows cracked. The temps inside a car will reach deadly temperatures amazingly fast. It’s the greenhouse effect at work.
I’d say it greatly depends on how much breeze there is and how far the windows are rolled down, eh?
My MG Midget convertable didn’t.
While I completely agree that it is a horrible idea to leave pets and children in the car on a hot day, this is the SDMB and I would like to see evidence of this. Are you saying that a baby or a poodle will die at exactly the same time in one car as opposed to the other test car right beside it with the windows cracked 5 inches? There has to be some increase in longevity to the point of surviving quite a while with the windows rolled down all the way. I need to see this tested scientifically.
Is that needed. I don’t know about the cars you guys have but non of mine have been airtight.
The temperature increase in a car out in the sun, while it can be significant, is nowhere near enough to cause a pressure increase sufficient to pop out a window. Even assuming a rise from an ambient temperature of 80 degrees F to 200 degrees F, we’re talking about a deltaT of 66 Kelvins. A quick-and-dirty calculation using Gay-Lussac’s Law (P[sub]1[/sub]/T[sub]1[/sub] = P[sub]2[/sub]/T[sub]1[/sub]) and assuming an ambient pressure of 1 bar (a bit low, so we’ll round up to 15 lbs/sq. inch), we get a pressure, at 200 degrees, of 1.22 bar, or a touch over 18 lbs/sq. inch. That’s a reasonably impressive 20% increase in pressure, but hardly enough to pop out a window, I shouldn’t reckon. And as another poster mentioned, cars aren’t airtight. This dog won’t hunt.
I’m not sure about that pressure valve, but most (all?) cars have a valve type ‘thing’ somewhere so the AC/Heat/Vent can work properly. They’re usually located on the side of the car towards the rear hidden by the bumper. You can see them in cars that have been rear-ended.
Bullshit, they call it the hood (convertible top to us colonials) 
Leaks like a sieve, water, air whatever.
The “dim dark days of long ago” are the key words here, I think. I remember when I was a child in the 1960s, my Dad always insisted that the windows be cracked a bit when the car was parked on a hot day, just so they wouldn’t pop out.
There may have been vents in those old cars to equalize pressure, and even if there weren’t, there may not have been enough pressure to pop a window. But at least to Klondike Geoff and my father, the belief was there. Who knows how many others believed the same thing?
Now, on a somewhat related question, how did this belief come to be? Have there been actual cases of windows popping out of a hot car? Or is it a “well, I heard that it happened to a friend of a friend” kind of urban legend?
I just saw that commercial. The outside temp was 107 F, while the inside was 70-something. It was this product (WARNING: annoying audio website). This site: Omaha News, Weather and Sports - Nebraska News - KETV NewsWatch 7 seems to suggest it sucks, although it’s hardly a scientific study.
I always understood that it wasn’t to relieve pressure, but to enable some kind of air circulation through the car.
I’ve noticed that it makes a difference, but not a huge one - I still wouldn’t leave a person or pet in the cart with the windows merely cracked.