defrosting windscreen

All you need is a bigger bucket.

I've been using tepid water for years. When the water has got a bit warmer from the hot tap, the worst I have heard is a creek from the seals.

HTH

Dave

windscreen breaking from the application of water. Might the old wive's tale have originated in much earlier times, when glass technology was not what it is today, and screens were more easily shattered? I've used the water method for thirty-odd years with no problems.

Tempered glass windscreens were created by heat treating the glass, so I would say that they were even less likely to shatter than modern laminated screens. I suspect it is that people knew that you should not plunge thick glass into boiling hot washing up water and assumed that the same would apply to any glass with any volume of heated water, whatever the temperature. I used water from the hot tap for many years, before getting a garage, and, like you, never had a problem.

Colin Bignell

So the RAC isn't above perpetuating old wive's tales then?

I find on a pool car at work that if I look down at the speedo then back up at the road my eyes briefly focus on the wires. I wouldn't buy one.

Chris

I had a similar experience, but now I own a Mondeo, don't notice the wires at all, and certainly would not swap for an unheated screen.

Chris

I use boilng kettles sometimes.

chief danger is it may freeze again.

Physics is more complex than you seem to think. Google for "Mpemba effect".

Douglas de Lacey

Interesting benefit I hadn't expected when I gravelled my drive - gravel is completely immune to icy patches that make you fall on your arse unexpectedly.

Dave

Following up to david lang

I have found my blocks over concrete are quite good, I assume because it takes an age for them to get cold. SWMBO-Mums crazy pazing only needs damp to make it an ice rink. On gravel, we have it at the back and had to bring range cooker in that way, try moving a heavy cooker on a delivery mans "skateboard" over gravel :-(

Best scraper about, nice an flexable follows the curve of the glass well.

Quite. Those using even warm water obviously don't have decent frosts. I've had the aerosol squirty stuff freeze on the windscreen before now and frequently go very thick. Scraping cars with -10C air temp and probably another 5 or 10 lower on the glass is not my idea of fun even with gloves on.

Naw, out a few minutes early start the engine press demist button, note change in engine note as the front and rear heated screens come on. Couple of minutes later just wipe the melted frost off with the wipers. B-)

erm, no it won't - think about the chemistry first.

Ice is a lattice structure (like a diamond), and it takes energy for the molecules to move into the lattice. In hot water, the molecules are moving rapidly, and can therefore form the lattice quicker than cold molecules which have very little energy.

That's why I said go and try it if you don't believe me - 2 containers of water in a freezer (one hot, one cold), the hot one will freeze faster than the cold one.

I've done it many times.

Hey - that's physics, not chemistry. Another explanation is that the hot container melts any frost and is in much better contact with the freezer's cooling tubes. The cold container is sitting on a nice insulating blanket so can't lose heat as quickly. It's also been suggested that the hot container has convection currents and is more turbulent by the time it's cooled down to the same temperature as the cold one was, and from there freezes more quickly.

-- LSR

The message from "Alan" contains these words:

Are you suggesting that ice forms at temperatures above zero degrees Centigrade?

I don't think he is, but water at zero degrees does not have to be ice, it can still be liquid. In fact super cooled water is liquid at negative degrees. Put a solid into the liquid and the resulting current provides enough energy for the molecules to lattice up and form ice.

Also water does strange things between zero and four degrees centigrade, explains why my fish pond doesn't freeze solid.

Dave

The message from "someone here" contains these words:

But if the water is hot first it has to cool. Once cooled its molecules have lost that rapidity of motion the previous poster refers to above.

AIUI water is at its most dense at 4C so ice forms on the surface. However given a severe enough frost you fish pond would freeze solid.

It would have to be a pretty hard and long frost to freeze a decent fish pond solid in this country.

As you say water is most dense at 4C, so it sinks to the bottom of the pond. As the surface of the pond gets colder it gets *less* dense and floats on the 4C water below. Convection stops and the only way the lower water is going to freeze is by conduction, ice is a pretty poor conductor of heat and the lower levels are in the relatively warm ground as well.