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  #1  
Old 10-07-2009, 07:55 PM
mangeorge mangeorge is offline
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Hot water on a cold windshield?

I've heard that pouring hot water on a cold windshield will shatter it, but I've seen it happen or talked to anyone who actually experienced it. You know our disdain for anecdotal evidence, so I come here for the Straight Dope.
I, and a lot of people I've known, have carried pichers of hot tap water out and poured it on frosty windshields with zero ill effects. But I've never lived in a truly frozen part of the country.
I ask 'cause my lazy old (64 yrs) butt is looking at getting one of these babies.
Peace,
mangeorge
BTW; It heats the fluid to 125-135F
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  #2  
Old 10-07-2009, 07:58 PM
Johnny L.A. Johnny L.A. is offline
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One frigid desert morning I started the car and turned on the defroster. I went inside to do something, and I heard what sounded like a .22 shot. When I went outside there was a long crack along the bottom of my windshield. I surmised that the warm air was enough to cause a temperature differential sufficient to crack it. Pouring water on an icy windshield won't shatter it, as they're designed not to shatter. But it may well crack it.
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  #3  
Old 10-07-2009, 08:03 PM
ladyfoxfyre ladyfoxfyre is offline
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It's happened to me before, when I lived in Colorado. Didn't shatter it, but significantly cracked the windshield.
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  #4  
Old 10-07-2009, 08:09 PM
GreasyJack GreasyJack is offline
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I've also had windshields crack just from the defroster (after letting the car warm up without the defroster on and then as soon as I turned on the defroster full-hot: crrrrrack), but it was in subzero temperatures-- not like anything you're going to get in the Bay area.
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  #5  
Old 10-07-2009, 08:32 PM
sweetie pea sweetie pea is offline
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Story I was told by co-worker who was from Mexico and married into Chicago [I'm sure many of us can sympathize; I myself married into Chicago from the lower midwest]:

First winter in the states, he went out one morning to find the windshield of the car he and his wife shared all iced up. He had no idea what the normal procedure was in this situation, but there seemed a logical solution. His wife was still showering, oblivious, as he heated the pan of water. Wouldn't she be surprised that he figured out what to do! Wouldn't she be thrilled with his thoughtfulness!

...

Us, wincing, "So, did it crack the windshield?"
Him, shrugging, "No. It just made more ice."

Last edited by sweetie pea; 10-07-2009 at 08:32 PM.. Reason: can't spell
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  #6  
Old 10-07-2009, 09:03 PM
JayRx1981 JayRx1981 is offline
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Well, speaking from experience, the opposite (a summer hot interior to a car) plus cold water from a hose (meant to wash said car) led to a huge crack in my first car's windshield. I imagine the opposite conditions leading to a cracked windshield is equally true under at least some circumstance. But I've never heard of a windshield shattering.
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  #7  
Old 10-07-2009, 10:07 PM
Northern Piper Northern Piper is offline
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I had a windshield crack as Johnny L.A. and GreasyJack describe. I swept the snow off the windshield itself, but didn't clear it away from the base, where the windshield wipers are, because I could see well enough.

Then I turned the heater on high.

Cracked all along the snowline at the base of the windshield.

On the other hand, I've seen water poured on a frosted up windshield, and it didn't crack, but the surrounding temperature was only a bit below freezing (this was in South Australia in their winter).

So, I wouldn't be surprised if cold water could cause a windshield to crack, in the right circumstances. I certainly wouldn't use it in our winters up here in Saskatchewan. That's what scrapers are for.
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  #8  
Old 10-07-2009, 11:27 PM
beowulff beowulff is offline
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One typical Arizona summer day, I used my windshield "squirter" to clean the windshield. The result was an immediate crack from top to bottom. I don't do that any more...
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  #9  
Old 10-08-2009, 07:43 AM
mangeorge mangeorge is offline
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It seems that many luxury cars have heaters for their winshield washers.
Some GM vehicles did, but discontinued them because of shorts (electrical, not Hanes) in the wiring and not related to the water temp.
I'm thinking the problem might be in the volume of warm water.
Also, some windshields are improperly installed (not bedded?) and are under stress all the time.
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  #10  
Old 10-08-2009, 07:54 AM
Serenata67 Serenata67 is offline
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It's the same thing that happened to another SDMB poster. Except his was home cooking and not hot water that cracked the glass.
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  #11  
Old 10-08-2009, 09:05 AM
FoieGrasIsEvil FoieGrasIsEvil is offline
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I suspect the likelihood of this happening goes up orders of magnitude if you already have an imperfection in your windshield glass, like a rock chip. The cracks will usually emanate from there.
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  #12  
Old 10-08-2009, 09:06 AM
FluffyBob FluffyBob is offline
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As a Canadian I am surprised someone would use hot water to clear ice off a windshield. Seems a lot of bother, if no ice scraper is handy, a cd, or cassette case case or any thing with 2+ inches of edge (preferably plastic) will do the trick. Start the car, set it to defrost and crank the fan, scrape your window and go. If its truly cold start your car five minutes before you have to leave.

I have to assume people only would use hot water if they are really unfamiliar with the problem, because really all you need is five minutes or almost any somewhat rigid plastic object.
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  #13  
Old 10-08-2009, 12:27 PM
AuntiePam AuntiePam is offline
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Quote:
Originally Posted by FoieGrasIsEvil View Post
I suspect the likelihood of this happening goes up orders of magnitude if you already have an imperfection in your windshield glass, like a rock chip. The cracks will usually emanate from there.
That's been my experience. I've poured warm (not hot) water on iced-up windshields -- no cracks. But I had a chip in a windshield and the first cold day when I turned on the defroster, the chip became a crack.

Now I keep a respectable distance when I'm behind a truck loaded with gravel, and semis.
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  #14  
Old 10-08-2009, 12:51 PM
cantara cantara is offline
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In the dead of winter (probably -15C) I had taken the car to a car wash. It was filthy with salt and road grime and the windows (all of them) were difficult to see out of. The very small crack just above the rear view mirror turned into a foot long crack as the wash started. The film between the layers of glass kept the inside layer intact, but the crack was obvious and we had to replace the windshield.

They sell those heaters here as well, so the likelyhood of damage must be limited to glass that already has minor damage. Also the temperature difference will also determine the chance of cracking. I would doubt that the Bay area would require too much caution. By the same token, I'm not sure how much benefit would be realized over simple winter washer fluid (not water).
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  #15  
Old 10-08-2009, 01:13 PM
Swallowed My Cellphone Swallowed My Cellphone is offline
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I've had it happen more the other way: warm to cold. One of my first Canadian winters, there was a freak-day of mild weather with temperatures getting almost balmy. Overnight there was a very sudden cold snap that dropped temperatures very fast. My rear car window shattered. "Shattered" as in the full spider-web grid thing happened and most of the window had dropped into the backseat like translucent gravel.

My buddy and I looked at what was left still attached to the window frame, and it kind of looked like the glass was shaped in a bit of a wave. The top three inches that were left of my window in corss-section looked undulated, sort of like: ~~~~ when it should have looked like: ------.

Our best guess was that the metal strip that held the window in place had contracted way faster than the glass itself. If that'swhat happened, I can see how throwing hot water on the glass could have a similar effect, only by expanding the glass faster than the cold frame.

ETA: the "undulating" part is supposed to look like a bunch of squiggles. WHen I see it in the Dope font, it looks all straight.

Last edited by Swallowed My Cellphone; 10-08-2009 at 01:16 PM..
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  #16  
Old 10-08-2009, 01:24 PM
Johnny L.A. Johnny L.A. is offline
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Quote:
Originally Posted by Swallowed My Cellphone View Post
My rear car window shattered. "Shattered" as in the full spider-web grid thing happened and most of the window had dropped into the backseat like translucent gravel.
I suspect a neighbour's riding lawnmower kicked up a piece of gravel, which then his the lower-rear window of my Prius. It also shattered and fell apart. (Why this guy felt the need to ride his mower out of his yard, drive on the road the length of my property, and then turn around in some gravel across the street I'll never know.) I suspect that on many or most cars the rear glass is not laminated, as the laminated glass ('shatterproof glass') is intended to be a safety measure in a forward crash.
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  #17  
Old 10-08-2009, 01:50 PM
brossa brossa is offline
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I was a passenger in the back seat of my parent's Horizon one subzero night when the rear windshield shattered as a result of the electric defroster being turned on. Glass gravel ended up all over the back deck of the car, down my neck, etc. I suspect that there was a narrow spot in the wiring that heated up faster than the other sections and led to the break; once it started, though, it was catastrophic.
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  #18  
Old 10-08-2009, 02:30 PM
EmAnJ EmAnJ is offline
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Hm, well, here's one from the opposite experience.

My husband warmed water and poured it on the windshield of both the car and the truck a number of times last winter (Canada) with no problems at all. I'd say he did this around 50 or 60 times over the winter season.
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  #19  
Old 10-08-2009, 07:08 PM
mangeorge mangeorge is offline
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Quote:
Originally Posted by FluffyBob View Post
As a Canadian I am surprised someone would use hot water to clear ice off a windshield. Seems a lot of bother, if no ice scraper is handy, a cd, or cassette case case or any thing with 2+ inches of edge (preferably plastic) will do the trick. Start the car, set it to defrost and crank the fan, scrape your window and go. If its truly cold start your car five minutes before you have to leave.

I have to assume people only would use hot water if they are really unfamiliar with the problem, because really all you need is five minutes or almost any somewhat rigid plastic object.
Hi, neighbor.
Actually, as an USAian, it's not a lot of bother to turn on the windshield washer which sprays a mist of hot (warm by the time it hits the glass) water.
And I think that might be key to this discussion, that the volume of heated mist compared to the mass of the ice and glass is so small that it quickly gives up it's heat, melting the ice.
Warmed air from the defroster keeps coming at a high temperature, and is concentrated at a relatively small point on the glass. You can see that as it clears the frost on the inside of your windshield.
Make sense?
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  #20  
Old 10-09-2009, 12:56 AM
t-bonham@scc.net t-bonham@scc.net is online now
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Quote:
Originally Posted by FluffyBob View Post
As a Canadian I am surprised someone would use hot water to clear ice off a windshield. Seems a lot of bother, if no ice scraper is handy, a cd, or cassette case case or any thing with 2+ inches of edge (preferably plastic) will do the trick. Start the car, set it to defrost and crank the fan, scrape your window and go. If its truly cold start your car five minutes before you have to leave.
A few years back, a crew of us from Minnesota were on a business trip to Alabama, and at a convenience store, saw a miniature windshield scraper, with about a 1/4 inch blade! We were astonished, both that they ever had to scrape ice from their windshields in Alabama, and that they used such a tiny scraper to do it (but maybe they only got little patches of ice?).

Turned out those were for scraping off the covering on scratch-off lottery tickets. (Apparently lots of Alabamians have big nails, that they don't want to damage by actually scratching off the scratch-off lottery tickets.)

We persuaded the store clerk to give us several of them. They made neat gag Xmas gifts for relatives back in Minnesota!
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  #21  
Old 10-09-2009, 09:41 AM
bordelond bordelond is offline
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Quote:
Originally Posted by FluffyBob View Post
As a Canadian I am surprised someone would use hot water to clear ice off a windshield. Seems a lot of bother, if no ice scraper is handy, a cd, or cassette case case or any thing with 2+ inches of edge (preferably plastic) will do the trick. Start the car, set it to defrost and crank the fan, scrape your window and go. If its truly cold start your car five minutes before you have to leave.
There seem to be a lot dependencies to this. An iced windshield at 30 degrees F is a far, far cry from the same at 30 degrees F. From my experience, you can safely pour warmish hot (NOT boiling) water all over the 30 degree windshield with reckless abandon. I've got many dings and stars in my windshield, and never have come close to getting a crack from pouring the hot water to remove ice.

Now then -- I am in Louisiana, and it's uncommon to wake up to weather colder than the high twenties with ice on the windshield (the rare part is the temperature after sunrise being so low, not the presence of windshield ice). What happens much more often is that the overnight low will be something like 25-30 degrees F, but the morning drivetime temperature will have risen to about the mid thirties. Because of the humidity, ice commonly deposits on windshields in the dark of night, and is still there in the hour or two after sunrise. Perhaps if the ice is already slowly melting, it's ever so much safer to our the hot water on it ... maybe the ice isn't "gripping" the windshield so tightly.
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  #22  
Old 10-09-2009, 09:45 AM
Colophon Colophon is offline
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I use just slightly tepid water - not even really warm. I've never had any cracking problem, but we don't get really cold weather here in southern England (lowest overnight mins are usually around 20F a few times a year).

If using tepid water, you need to leave the wipers going once the frost has melted, otherwise it will refreeze.
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  #23  
Old 10-09-2009, 09:50 AM
bordelond bordelond is offline
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Quote:
Originally Posted by t-bonham@scc.net View Post
We were astonished ... that they ever had to scrape ice from their windshields in Alabama ...
If we have to get ice off our windshields in New Orleans, they certainly have to in Alabama, as well. I'd expect northern Alabama to get quite cold, actually. Not Minnesota cold, but probably getting down around 10-12 F at some point every winter.
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  #24  
Old 10-09-2009, 09:51 AM
bordelond bordelond is offline
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Missed the Edit window. In post #21 above:

An iced windshield at 30 degrees F is a far, far cry from the same at 30 degrees F.

is supposed to read:

An iced windshield at 30 degrees F is a far, far cry from the same at 0 degrees F.
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  #25  
Old 10-09-2009, 09:54 AM
bordelond bordelond is offline
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Originally Posted by Colophon View Post
I use just slightly tepid water - not even really warm. I've never had any cracking problem, but we don't get really cold weather here in southern England (lowest overnight mins are usually around 20F a few times a year).
I am betting that as long as whatever you're doing doesn't vaporize the ice instantly, the risk of cracking is minimal. Also, there seems to be a sweet spot temperature-wise (circa 25-35 F) where gentle melting is possible without rapid re-freezing.
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  #26  
Old 10-09-2009, 10:08 AM
mangeorge mangeorge is offline
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Okay, ahead and ordered the thing. I can't help it. My name is mangeorge, and I am a gizmo addict.
So, I'll install it and sound the alarm here if it cracks my windshield within the next couple years. If it works good, maybe I'l post my excitement in MPSIMS.
Bub Eye
mangeorge
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Neither Windshield nor Bug am I.
Give us br'er rabbits.
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  #27  
Old 10-09-2009, 10:22 AM
Colophon Colophon is offline
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Handy if you ever need a hot shower while out on the open road, I suppose.
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  #28  
Old 10-09-2009, 12:30 PM
mangeorge mangeorge is offline
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Originally Posted by Colophon View Post
Handy if you ever need a hot shower while out on the open road, I suppose.
Also handy if you just want to get in the car, start it up and clear some light icing from your windshield and not have to play Nanook of the North.
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