defrosting windscreen

[Grumps]

I've always been told that you shouldn't use water as it could crack the glass. Is this true or one of those old wives' tales?

[Alan]

You shouldn't use hot water as this will re-freeze faster than cold water would(and for all of those people who don't believe me, go and try it).

Just buy some de-icer - or get a car with a heated windscreen

[Autolycus]

I used this method for years, on conventional and bonded windscreens, and had no problem using hot-tap-temperature water.

I now stand a 40 year old Ducal Aristocrat domestic fan heater (2.25kW) inside the car for a quarter of an hour or so on a frosty morning - thaws the windows, and makes the whole thing less unpleasant to get into. Costs about 2p on Economy 7.

[tarquinlinbin]

I always use warm to hot water (not boiling!) and it always does the trick. Sometimes you have to apply twice to remove all the frost if its really bad but it works well and you are not squirting horrible chemicals all over the place.

Remove antispam and add 670 after bra to email

[Dave Fawthrop]

| I've always been told that you shouldn't use water as it could crack = the=20 | glass. Is this true or one of those old wives' tales?=20

There is a standard way of breaking glass bottles cleanly to form a ?glass? using boiling water. So boiling water definitely breaks glass.

--=20 Dave Fawthrop

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[Lobster]

It's all about temperature differences surely, and changing temperatures quickly; the reason glass breaks is because it expands when it gets hot, and if that happens too quickly the glass won't warm up evenly, resulting in breakage.

Consider the following:

1. Take a wine glass out of the cupboard and fill with boiling water - it's unlikely to break.
2. Put it in a pan of cold water and bring to the boil on the cooker - again, not likely to break.
3. Put the empty glass in the freezer for a while, then remove and fill with boiling water - it'll almost certainly break, due to the rapidity of the large temperature change.

David

[Paul Andrews]

I wouldn't risk it. I've never seen why people just don't clear the windscreen as I do - with a credit card..

[Vass]

Yep jug of cold water, add a little hot till you can feel a change in the temp of the water (i.e. warm not hot) poor this over the screen - no probs in 20 years !!!

[David Hearn]

Have a think about the physics of that for a minute.

Hot water will never re-freeze faster than cold water. To freeze water much reach 0deg. Water which is 10 deg will freeze faster than water which is 40 deg given the same surface temperature of the windscreen etc.

When using warm/mildly hot water, you may get it re-freezing sometimes simply because the energy stored within the hot water applied isn't sufficient to raise the window temp above 0deg, but it will have raised it a little. Just keep putting more and more warm water on it until the temp has increased above 0deg and it stops freezing.

D

[Andy Burns]

some of the hot water will evaporate, the amount which is left will re-freeze in the same time as a similar amount of cold water.

[Dave Fawthrop]

| Dave Fawthrop wrote: | > On Thu, 12 Jan 2006 08:23:54 -0000, "Grumps" =

| > wrote: | >=20 | > | I've always been told that you shouldn't use water as it could = crack the=20 | > | glass. Is this true or one of those old wives' tales?=20 | >=20 | > There is a standard way of breaking glass bottles cleanly to form a | > ?glass? using boiling water. So boiling water definitely breaks = glass. |=20 | It's all about temperature differences surely, and changing = temperatures=20 | quickly; the reason glass breaks is because it expands when it gets = hot,=20 | and if that happens too quickly the glass won't warm up evenly,=20 | resulting in breakage. |=20 | Consider the following: |=20 | 1. Take a wine glass out of the cupboard and fill with boiling water -=20 | it's unlikely to break. |=20 | 2. Put it in a pan of cold water and bring to the boil on the cooker -=20 | again, not likely to break. |=20 | 3. Put the empty glass in the freezer for a while, then remove and fill= =20 | with boiling water - it'll almost certainly break, due to the rapidity=20 | of the large temperature change.

True but pouring boiling water onto a windscreen will produce a large temperature difference, and so may crack the windscreen. =20

--=20 Dave Fawthrop

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[The Reid]

Following up to Paul Andrews

or a £1.50 scraper you keep in the door pocket? That way you remove H20 from the car, rather than adding it,which surely isnt what you want. Especially on the opening windows, which should also be clear before you consider driving. IMHO in very cold weather its not safe to drive until the engine has warmed up enough to maintain clear unmisted windows. So out of bed 10 minutes early, start the engine and get scraping! YKIMS!

[sPoNiX]

Use warm water with a dash of dishwasher rise aid.

[Chris Bacon]

69p from Lidl.

The disadvantage with these scrapers is that they have straight edges, .: aren't so good for windscreens. Credit cards, and so on, are much better as long as the ice isn't too thick.

A pail of water from the cold tap is quick and efficient.

[Holly, in France]

Me too, never had a problem, water about 60 deg C here. Kids start the car, put on the heater and air-con for five minutes or so, do the hot water thing and put the wipers on, I go out at the last minute and drive to school. Easy peasy :-)

Incidentally I hired a Ford Focus in England recently with a heated windscreen, which I didn't need to use whilst I was there. Most of the time it was fine but once I started seeing the little lines I couldn't stop seeing them, if you know what I mean. Good idea but I wouldn't buy one unless they made the whole thing less visible.

-- Holly, in France Holiday Home in Dordogne, now with pool!

[david lang]

It's the thermal shock that breaks the glass, not the temperature. One part expands much faster than another.

Glass is made at something like 2000 centigrade after all.

Dave

[adder1969]

Windscreens aren't made out of the same glass as glasses are. I've used hot water for years and a friend uses boiled water out of a kettle. You're not immersing a frozen windscreen into a tub of boiling water - you're pouring a thin layer of hot water onto a cold windscreen so there's not huge energy transfers going on. If you put your hand into a bowl of very hot water you'll get scalded but if you splash a bit of that same water on you it probably won't do any damage at all. Some say that the water will freeze over almost immediately in which case you need to use more water. Some say to use rinse aid so the water rolls off before it can freeze but I've never needed to. I fill a jug up from the tap, go outside, pour it on the screen and other windows, jump in the car then I'm off. All while next door have the car with the engine running and are scraping away at the windows with a scraper.

[.]

agreed.

I've done this for years with several cars and never broke or cracked a screen.

[sPoNiX]

Yeah, I recon that the layer of ice takes most of the thermal shock away.

Anyhoo, if the hot water is prone to re-freezing it can't be heating the glass very rapidly, can it?

sponix

[Dave Fawthrop]

| Dave Fawthrop wrote: | > There is a standard way of breaking glass bottles cleanly to form a | > ?glass? using boiling water. So boiling water definitely breaks | > glass. |=20 | It's the thermal shock that breaks the glass, not the temperature. = One=20 | part expands much faster than another. |=20 | Glass is made at something like 2000 centigrade after all

Glass is brittle as everyone who has broken a glass doing the washing up knows. Expand one bit in relation to another and it goes ping.

--=20 Dave Fawthrop

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