Winter driving - windscreen secrets

Visibility is a pretty vital thing when driving, so don’t take any shortcuts on those cold mornings this winter – make sure you can see, writes Damien O’Carroll.

While it is becoming increasingly common for new cars to have remote start and automatic defrost/defog features (particularly if they are made by manufacturers based in cold climates) new cars without these features and older cars still suffer from that dreaded lack of visibility on cold mornings – a foggy windscreen on the inside or an iced up one on the outside.

What to do about it? Here’s a few tips.

Demisting 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, you 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. It may even make things worse if you are badly out of shape and the sheer exertion of wiping the windscreen gets you breathing hard...

If you have an older car without air conditioning, 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.

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.

But that takes time and wastes fuel, plus would also make for an awkward conversation with your insurance company if someone decides to drive off in this conveniently warm car that is sitting there running.

A free and far more ecofriendly 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.

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.

And 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.

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.

Again though, prevention 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.

If you are lucky, your car will have a self-defrosting windscreen. Not many do though.

Don’t use metal scrapers and never use hot water to clear ice from your windscreen.

This is called ‘‘port holing’’ and it is very dangerous. A bit of prevention the night before can save effort in the morning.

The demister is the best way to clear your windscreen quickly.