gar074 said:

But if there's an existing weakness in the screen (eg from a stone chip), putting hot water on a frozen screen may well propagate a crack. It's happened to me twice, and my other half (who is a materials scientist and an expert on fracture mechanics) gave me a right ticking off, especially the second time it happened.

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Yep; so with a few more tests you'll be able to advise on the critical flaw size?

Have you had the talk re tearing energy and crack growth rates in rubber bushes yet?!

It's shout also be easy to test the windscreen heating with a infrared thermometer as it should should show up such a large them difference easy especially if it's like you show on your pictures

chris3234 said:

It's shout also be easy to test the windscreen heating with a infrared thermometer as it should should show up such a large them difference easy especially if it's like you show on your pictures

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Thank you. My perception is that actually the elements don’t get very hot. Like the rear screen, they only need to be a few degrees above ambient to be effective. Dealer now have the photos...

Panda IIs said:

Have you had the talk re tearing energy and crack growth rates in rubber bushes yet?!

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At the dinner table, we talk of little else

As promised, an update after talking with the dealer. Initially they wanted to have the car to see this for themselves, but I instead I sent my photos and time-lapse video to them. They looked, showed it to the warranty team, and agreed that yes, it was faulty. They approved the ordering of a new heated screen, and it is being fitted on Monday. Result. thank you to those who suggested sending the photos. I think the Tier 4 and Lockdown has helped here a bit too... maybe one small good thing to have come from it. The car will be used for the first time in eight days when I drive to the dealer on Monday!

Yay. Glad to hear the warranty claim was approved.

We won’t be having these issues in 10-20 years time when we’ve all got EVs with pre-heating. Can’t beat getting into a 24C cabin and just driving right off

Most Easterly Pandas said:

Yay. Glad to hear the warranty claim was approved.

We won’t be having these issues in 10-20 years time when we’ve all got EVs with pre-heating. Can’t beat getting into a 24C cabin and just driving right off

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A wonderful benefit, for those with off-street parking. Or suffer a reduced range, which might be important for some.

murphyv310 said:

Hi.
The temperature shock and unequal expansion effects different types of glass in different ways. Pour boiling water into a milk bottle and it'll shatter, do that with Pyrex and it won't. Car glass won't crack even with boiling water as car glass can have uneven heating, on occasions when the sun is at certain positions its rays can pass through side windows at an angle that'll pinpoint light at another window giving spot heating. From what I've been told in the past glass used in motor vehicles is thermal shock resistant and has been from the 60s. The thin wires in a heated screen get very hot and if this was the case the screen would suffer with thermal shock far worse than hot water as the water is not spot heating the glass and is cooled on contact, plus its over a much larger area.
I've cleaned all my windows on all my cars since 1971 this way with no issues.
Again each to their own on how to clear iced or snow covered windows.
Take mind many just seem to clear a small part in front of them and not clearing all windows is a road traffic offence.

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In the late eighties, I watched the toughened screen on an Austin Maxi gently craze across, then expand and blow outwards. It had been parked against the showroom wall, and the sun on a frosty morning heated half the screen. As that half defrosted, and the internal temp increased, the screen cracked, and the warmth inside caused enough pressure to push the screen out.
Great bit of science in action.

Christmas '88, it happened to my car. Fiat 131, toughened screen, parked opposite my mother-in-law's cottage in Bognor. Looked out the window around 8am, all covered in frost. Two hours later, screen popped, due to shadow across half as the sun rose. Same situation as the Maxi a year or two earlier.
This was Christmas Eve, early afternoon a nice man arrived and fitted a new screen, laminated this time.

chris3234 said:

It should also be easy to test the windscreen heating with a infrared thermometer

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These screens are very effective in doing what they do.

It's easy to test the windscreen heating by switching it on when there's some condensation or frost on the screen. Any continuity breaks in the heating elements will be apparent almost immediately.

Worth doing if contemplating a secondhand purchase of a vehicle with a heated screen, as many used car warranties won't cover a minor defect like this, and these screens aren't cheap.

murphyv310 said:

Car glass won't crack even with boiling water

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This is dangerously wrong and bad advice; I've seen several screens cracked as a result of pouring boiling water on them. Just because you've done this on your car without issues doesn't make it safe.

As has been said, it only takes one existing hairline crack and the additional thermal shock could turn it into a major fault. Almost all screens have small imperfections due to stone impacts; this is just about impossible to avoid.

Interestingly the instructions for Pyrex bakeware contain a warning never to use it if cracked or chipped, as it may fail catastrophically if placed in a hot oven.

portland_bill said:

A wonderful benefit, for those with off-street parking. Or suffer a reduced range, which might be important for some.

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You don’t need off street parking to precondition most EVs as they don’t need to be plugged in

Ah, the same reduced range that most vehicles suffer with in the winter due to reduced efficiencies in the cold

jrkitching said:

Interestingly the instructions for Pyrex bakeware contain a warning never to use it if cracked or chipped, as it may fail catastrophically if placed in a hot oven.

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They create a lot of very tiny pieces if they break when dropped, so an 'explosion' in a hot oven would be quite frightening. Likely to break the oven door too.

A neighbour used to pour hot water over his screens every morning. Made a lovely loud 'crack' one day.

Only time I've used warm/hot water for a defrost was with the BSM learner cars. The roof sign is held by magnets, and they don't stick well to frost. Hot water across the part of the roof with the protective vinyl melts the frost, and all the water ran off without touching glass. Then a quick wipe dry and on with the sign.

jrkitching said:

This is dangerously wrong and bad advice; I've seen several screens cracked as a result of pouring boiling water on them. Just because you've done this on your car without issues doesn't make it safe.

As has been said, it only takes one existing hairline crack and the additional thermal shock could turn it into a major fault. Almost all screens have small imperfections due to stone impacts; this is just about impossible to avoid.

Interestingly the instructions for Pyrex bakeware contain a warning never to use it if cracked or chipped, as it may fail catastrophically if placed in a hot oven.

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Hi.
Sorry I don't agree.
I've been working with glass for many years. In my trade as a TV engineer I have seen some horrendous things.
When I worked with Sony the service manager was trying to get a fault to show up on a Trinitron CRT. The tube was hot and had been running for hours, he then decided to spray the gun assembly with a can of freezer which in my opinion was madness but it didn't crack. Milk bottles of course will shatter with sudden changes. Having had the vast majority of cars with AS1 Laminated glass I was told by authority they do not get damaged or crack with spot heating. The thing is when you pour hot water on a screen, you don't do the little bit in front of you, you do it all and the water cools very fast as it's not a constant stream of hot water in one area at a time. I'd not be so keen on doing this on toughened glass. Side windows are toughened and thinner so I only use water that is around 40 to 60c.
I've discussed this with a friend who is a retired glass blower and he assured me it's perfectly safe. Putting boiling water in a bottle will explode as there is a large pool of hot water in the bottom of the bottle and the rest is cold so the expansion is uneven thus the bang.

As I said in my previous post each to their own, I'm not telling them what to do, it's their choice, just like everything in life.

Most Easterly Pandas said:

Ah, the same reduced range that most vehicles suffer with in the winter due to reduced efficiencies in the cold

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But I can top mine up in minutes, in lots of convenient places. It will take a long time to get used to frequent waits to recharge.

Most Easterly Pandas said:

You don’t need off street parking to precondition most EVs as they don’t need to be plugged in

Ah, the same reduced range that most vehicles suffer with in the winter due to reduced efficiencies in the cold

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Fossil fuel powered cars suffer far less of a drop in range and efficiency to battery's powered car's they sufft a double whammy effect of heating drawing a lot of power and the cooler temps reducing the efficiency of the battery's

portland_bill said:

But I can top mine up in minutes, in lots of convenient places. It will take a long time to get used to frequent waits to recharge.

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Why waste minutes waiting about when you can spend seconds and go off and do something productive while it recharges.

How often do you plug your mobile in and stand by it just waiting while it charges

chris3234 said:

Fossil fuel powered cars suffer far less of a drop in range and efficiency to battery's powered car's they sufft a double whammy effect of heating drawing a lot of power and the cooler temps reducing the efficiency of the battery's

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Agree, but they still suffer a loss. Ask many and they’ll deny it

murphyv310 said:

I've discussed this with a friend who is a retired glass blower and he assured me it's perfectly safe.

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In an ideal world yes, without any pre-existing flaws. On a windscreen with stone chip damage (possibly smaller than you can resolve by eye) then hot water on a cold screen is asking for trouble. My wife didn't believe me until she had to get a Volvo screen replaced.

There's a scraper by the front door now.

My heated window of my November 2012 Panda 85TA did not work as good as it use to be.
There where some single lanes not working as fast as the rest, but ad the end a clear window.

Miss it in de 595 Turismo.

For all the boiling water evangelists I have a very simple question.

Why take the risk?