Boiling water onto cold windscreen?

The windsreens slopes more?

The message from WM contains these words:

The windscreen is angled towards the sky, which on a clear night radiates hardly any IR - so the balance of heat radiation is strongly in favour of leaving the screen.

The side windows are more vertical and more than likely face at least partly towards a wall or vegetation, which though cold are still well above the temperature of the sky. Thus, the balance of heat flow is less stronly away from the window.

You can acheive the same effect for the screen by parking it facing a building.

Or on a really, really steep slope.

A credible explanation, not to mention the materials/composition of the windscreen and those of the side windows are different. :)

??

I use tap-hot water. It works pretty much instantly even after a -5C night with thick clear ice on the screen.

Why would you need more than that?

Probably terrified of cracking the screen, and just waiting to gloat when yours finally goes...

The message from "Lin Chung" contains these words:

Ah, but it happens with sloping rear screens too - and they're more similar to side windows than to front screens.

Cracked from side to side - needed a new screen, only heated along the bottom

No this heats up the whole window

I know this is going back a bit, but I was talking with my Dad about this yesterday, and he's an engineer type. He was saying that the boiling water affects the laminate between the glass, which causes the tiny cracks in the laminate, and because they're underneath the surface of the glass, they can't be removed / polished out etc.