Icy windscreen - warm water safe to use?

[jep]

I tend to use luke warm water to clear an icy windscreen. In 35 years, no issues. I occasionally use a scraper but I won't use de-icer as I see that as lazy and an unnecessary expense.

I was admonished by a vehicle recovery driver last week, he claimed it could crack the windscreen. 

Is that true? I doubt if luke warm would, I don't use boiling water but could that shatter a windscreen?

The only car I have with a heated screen is the 340R which ain't often icy........

Justin

 

[Bibs]

It could crack the windscreen, especially if it has stone damage. Warm water in a plastic bag is a good idea if you're not keen on de-icer.

 

[Bravo73]

Personally, I find that water out of the cold tap is more than enough. Unless the ambient temperature is really low (ie -5 or below), then the temperature differential is more than enough to melt the ice.

[jep]

I do wonder what a scientific answer would be....not expecting one but I'd like to understand the genuine science of hot water on laminated or toughened cold glass. 

Justin

[C8RKH]

Not scientific but Autoglass know a thing or two about windscreens I suppose!

How to Defrost your Windscreen and Rear Window

With Water:

Firstly, to avoid damaging your windscreen, you should only apply lukewarm water when you defrost your windscreen. You will find that the amount of water required will depend on the size of the windshield or rear window that needs defrosting. Apply the warmed water to the frozen area by pouring or splashing it directly onto your windscreen. The ice should quickly soften and melt to the point where it can be wiped away with a cloth, glove or your windscreen wiper.

Top Tip:

Applying boiling water to your windscreen not only risks damaging the glass. Believe it or not, in extremely cold conditions, hot water can freeze faster than cooler water. So, if you apply hot water to a frozen windshield, you may find it refreezing again soon.

[andydclements]

I do the same as @Bravo73, I have even cracked a screen that was seemingly undamaged before and that was just by pressure-washing the car on a hot day.

[mg4lotus]

@C8RKH Known as Mpemba effect. Some experiments were done on the telly a few years ago that showed hot water freezing faster than cold but the mass of the water had to be large enough to allow convection currents to form (they used buckets of water). So although it may be interesting it may not be relevant to water being poured on screens

[eclat22]

When at home, I have an electric blow heater that I put in van for 5 minutes to heat the cab up and de ice it before leaving for work.

[Bibs]

Pats electric car with phone enabled defrost

[exeterjeep]

Wife's car has heated front screen. But does not get too much use down here in Devon. 

Certainly would not pour hot water on an icy screen or cold water from a hose or similar on a baking hot screen in full sun.

[LotusLeftLotusRight]

What’s wrong with leaving a piece of cardboard box under the wiper overnight?