What is the easiest and safest way to defrost your windscreen?

Thursday, 24 June 2021

What's the best way to get that ice off your windscreen on a cold winter's morning? Here's the best way.

As the cold blast creeps further up the country, with temperatures near Auckland dipping to zero or below, a lot of people will dealing with that old winter curse – clearing your car’s windscreen, both of ice on the outside and condensation on the inside.

Defrosting the outside

The obvious way to get rid of ice on the outside of your windscreen is to start the car, wind the heat right up and wander back inside for another coffee.

Pouring luke warm or room temperature water on an icy windscreen is the best and safest way to melt ice on a windscreen.

But that takes time and wastes fuel – a free and far more eco-friendly option is luke warm or room temperature water. Pouring this over the windscreen will quickly melt off a light frost, while a heavier one may require a bit of scraping with a plastic scraper, just never use a metal one, as it can scratch the glass.

**READ MORE:

Always use a plastic scraper to remove ice – a metal one could easily scratch your windscreen.

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Don’t just clear a small area of the windscreen – that’s called ‘port-holing’ and it is very dangerous.

* Winter motoring: is it OK to warm up your car before driving?

What about when your windscreen fogs up on the inside? Get the air moving – cold at first, then slowly increase the temperature.

Also, never use hot water - while it will melt the ice quickly, the drastic temperature change could cause your windscreen to crack, making a cold morning even more unpleasant.

After you have done this, be sure to turn your windscreen wipers on to clear the excess water so that it doesn't simply refreeze.

While commercial de-icer products are available, a homemade blend can do just as good a job – a mixture of 2/3 isopropyl alcohol or methylated spirits and 1/3 water (some say with a few drops of dishwashing detergent) sprayed on a frozen windscreen will do the trick, followed, again, by some easy scraping and wiper-use.

Air conditioning is the beat way to clear a fogged up windscreen, but again, start cold and increase the heat.

If all this seems like far too much effort on a cold day, then a bit of simple and easy preparation the night before is the easiest idea of all - putting an old sack, sheet or piece of cardboard over the windscreen the night before can save a heap of time and effort the next morning. Some people will recommend newspaper, but if it rains you will have a soggy mess to deal with in the morning.

One old remedy that surfaces every year is the theory that a mix of water and vinegar will defrost a windscreen. It doesn't, but it will stop frost forming if sprayed on the night before.

Defogging the inside

Why does the inside of your windscreen fog up? It's actually down to the amount of moisture the air can hold – warm, high pressure air can hold more water vapour, which is why it gets humid in summer, while cold, low pressure air doesn't hold as much.

So when you hop in your car on a cold morning, your breath is full of water vapour, but the cold air inside the car can't hold it all, so it ends up as condensation on the cold glass surfaces

So what is the best way to get rid of it?

Simply wiping the inside of the windscreen is an instant fix, but your breath simply pumps more moisture straight back into the air, so it is only a short-term fix at best.

If you have an older car without air conditioning (or it doesn't work), then starting the fan blowing on cold and slowly increasing the temperature as the air dries out is the best way - starting it on hot straight away just loads the car's cabin with more warm, moist air, making it actually slower to demist the windscreen.

Of course, if you have air conditioning, then that is the obvious and fast way to clear it.

If your car has a demist function, use that, but don't wind the temperature up if it starts off by blasting cold air into the cabin - it is working on the same principle mentioned earlier of drying the air out, then warming it up.

Prevention is possible as well, with a number of sprays and treatments available that do a very good job, if condensation is a big problem for you.

Then there are those old-time remedies - rubbing half a potato on the inside of the windscreen or cleaning it with shaving foam. Depending on who you talk to these either work brilliantly, or not at all. Probably worth a try, if you don't mind you car smelling of potatoes.