# If you leave your car windows up on a hot day.... **URL:** \ **Category:** Factual Questions\ **Created:** [July 31, 2008, 6:26pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386 "2008-07-31T18:26:03Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [July 31, 2008, 6:26pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/1 "2008-07-31T18:26:03Z")
…can the heat cause the window(s) to blow out? It’s just about to start raining here so there’s a mass exodus of people going outside to close the windows on their cars. Everyone seems to be in agreeance that the reason they do it is because if it gets hot enough the windows can be blown out. On it’s face it sounds a bit silly, but heated air will expand, so what say we? I’ve never heard of such a thing before right now. ---
**Author:** ![brewha](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@brewha](https://boards.straightdope.com/u/brewha)\ **Post date:** [July 31, 2008, 6:32pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/2 "2008-07-31T18:32:46Z")
While air does expand when it heats, it is compressible. So, even if your car were air tight, the air inside couldn’t expand enough to blow out your windows. And, since your car is not air tight, any expansion that does occur happily exits through the nearest crack. ---
**Author:** ![brewha](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@brewha](https://boards.straightdope.com/u/brewha)\ **Post date:** [July 31, 2008, 6:32pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/3 "2008-07-31T18:32:20Z")
While air does expand when it heats, it is compressible. So, even if your car were air tight, the air inside couldn’t expand enough to blow out your windows. And, since your car is not air tight, and expansion that does occur happily exits through the nearest crack. ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [July 31, 2008, 6:32pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/4 "2008-07-31T18:32:31Z")
The cabin of a car is hardly air tight. If it was, people would suffocate on long car rides. Also, the amount of expansion from, say, 20 C to 40 C isn’t very much. In absolute temperatures, that’s 293 K to 313 K. That would cause less than a 1% increase in pressure given constant volume. The real reason is to keep the car cooler by letting the hot air escape. ---
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [July 31, 2008, 6:38pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/5 "2008-07-31T18:38:42Z")
Awesome triple post. I didn’t think so, it sounds like a story someone made up to cover up the fact that they did something really stupid and didn’t want everyone to know. Thanks! ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 31, 2008, 6:41pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/6 "2008-07-31T18:41:51Z")
[QUOTE=Cluricaun] Everyone seems to be in agreeance that the reason they do it is because if it gets hot enough the windows can be blown out. . [/QUOTE] :smack: It seems pretty clear that the Straight Dope’s mission is going to take much longer than was previously thought… ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [July 31, 2008, 6:42pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/7 "2008-07-31T18:42:45Z")
If your car was air tight and the air expanded you’d get a cool “Pshhhh!” sound when you opened your car door like opening a 2-liter of pop. ---
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [July 31, 2008, 6:46pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/8 "2008-07-31T18:46:15Z")
[QUOTE=beowulff] :smack: It seems pretty clear that the Straight Dope’s mission is going to take much longer than was previously thought… [/QUOTE] True, but we got a three day extension on our subscriptions, so maybe that will help. 😉 And if this were only the dumbest thing I’ve ever heard from a coworker… ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [July 31, 2008, 6:52pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/9 "2008-07-31T18:52:07Z")
[QUOTE=Hampshire] If your car was air tight and the air expanded you’d get a cool “Pshhhh!” sound when you opened your car door like opening a 2-liter of pop. [/QUOTE] I’ve heard this when opening my gas cap. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [July 31, 2008, 6:52pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/10 "2008-07-31T18:52:08Z")
Not only is it not airtight, there are vents in the back, usually under the rear bumper so you can run your AC/Heater without pressurizing the cabin. ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [July 31, 2008, 7:13pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/11 "2008-07-31T19:13:27Z")
[QUOTE=Hampshire] If your car was air tight and the air expanded you’d get a cool “Pshhhh!” sound when you opened your car door like opening a 2-liter of pop. [/QUOTE] Plus, the door would fly open forcefully and hit you in the junk. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [July 31, 2008, 7:20pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/12 "2008-07-31T19:20:22Z")
[QUOTE=Cluricaun] It’s just about to start raining here so there’s a mass exodus of people going outside to close the windows on their cars. Everyone seems to be in agreeance that the reason they do it is because if it gets hot enough the windows can be blown out. [/QUOTE] I assume you’re saying this is the reason they leave the windows down in the first place (the obvious reason for their running out to close them being they don’t their cars wet inside). Jillions of cars have been parked for jillions of hours with the windows up in hot temperatures without the windows being blown out. Furthermore, car windows are notorious for their strength. Special tools are made to break them to allow exiting a submerged car, because even strong people can’t kick them into breaking. That notion that air pressure could break them doesn’t have any evidence to support it. What can happen sometimes is that car window glass will spontaneously shatter. It’s rare, but not unheard of. It happened on one of my cars, and it was parked with the windows shut on a hot day. There’s no way it blew out - it was an old convertible that leaked (air) like a sieve. And interestingly, most of the broken glass was on the inside of the car. ---
**Author:** ![FlyingCowOfDoom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/flyingcowofdoom/32/21776_2.png) [@FlyingCowOfDoom](https://boards.straightdope.com/u/FlyingCowOfDoom)\ **Post date:** [July 31, 2008, 8:35pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/13 "2008-07-31T20:35:38Z")
[QUOTE=Tom Tildrum] Plus, the door would fly open forcefully and hit you in the junk. [/QUOTE] This comment FTW! –FCOD ---
**Author:** ![lizardling](https://avatars.discourse-cdn.com/v4/letter/l/f4b2a3/32.png) [@lizardling](https://boards.straightdope.com/u/lizardling)\ **Post date:** [July 31, 2008, 8:42pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/14 "2008-07-31T20:42:20Z")
No. Otherwise the car glass industry in the South and other parts where summer gets to triple degrees, easy, would have a field day every summer. ---
**Author:** ![Flander](https://avatars.discourse-cdn.com/v4/letter/f/8c91f0/32.png) [@Flander](https://boards.straightdope.com/u/Flander)\ **Post date:** [July 31, 2008, 8:55pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/15 "2008-07-31T20:55:04Z")
[QUOTE=Tom Tildrum] Plus, the door would fly open forcefully and hit you in the junk. [/QUOTE] I’m cracking up thinking of this! Living in south Florida, I’m glad this isn’t true. I’d have to wear a cup every day in the summer! 😃 ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 31, 2008, 9:27pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/16 "2008-07-31T21:27:18Z")
I’ll tell you what **is** true, however: It’s possible to crack your windshield by squirting washer fluid on it during a very hot day. I know, because I watched it happen to my Jeep. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [July 31, 2008, 10:07pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/17 "2008-07-31T22:07:14Z")
[QUOTE=Gary T] It happened on one of my cars, and it was parked with the windows shut on a hot day. There’s no way it blew out - it was an old convertible that leaked (air) like a sieve. And interestingly, most of the broken glass was on the inside of the car. [/QUOTE] Was this phenomenon accompanied by a missing radio, maybe? :dubious: ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [July 31, 2008, 10:12pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/18 "2008-07-31T22:12:02Z")
If you’re in doubt as to how non-airtight your car is … drive it into a body of water with the windows closed, and see how long it takes to sink. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [July 31, 2008, 10:39pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/19 "2008-07-31T22:39:05Z")
[QUOTE=CookingWithGas] Was this phenomenon accompanied by a missing radio, maybe? :dubious: [/QUOTE] No, though at first I thought maybe a ball or rock had done it. The car was in my driveway, I was in the house and heard a loud pop/glass breaking noise. I went right out and saw the broken window. No one else was around, some of the glass was inside the car and some was outside, and I never found any object inside the car that might have caused it. In talking to the glass company, I was informed that this type of spontaneous breakage has been known to occur. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 31, 2008, 10:50pm UTC](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386/20 "2008-07-31T22:50:12Z")
[QUOTE=Gary T] No, though at first I thought maybe a ball or rock had done it. The car was in my driveway, I was in the house and heard a loud pop/glass breaking noise. I went right out and saw the broken window. No one else was around, some of the glass was inside the car and some was outside, and I never found any object inside the car that might have caused it. In talking to the glass company, I was informed that this type of spontaneous breakage has been known to occur. [/QUOTE] I’d say a BB or .177 pellet is much more likely than some sort of mysterious spontaneous glass shattering. [Next page](https://boards.straightdope.com/t/if-you-leave-your-car-windows-up-on-a-hot-day/458386.md?page=2)