Frozen windscreens happen because as the temperature falls the windscreen releases heat faster than the plastic or metal body part of the car, because of the rapid cooling from the glass condensation and eventually water from rain will freeze creating its own layer.
Over the last few weeks we have tested a variety of methods and ranked them in terms of how easy they are, expensive, how quickly and effective each method is to completely clear the car. Each area was ranked out of 10 with an average score given. The tests were conducted on personal lease and business lease cars.
Least effective of our tested methods was the cars own fan and air conditioning. With the weather at just 0 Celsius, we started the car, turned the fan to full heat, pointed it at the windscreen and used full power with the air con on. After about 5 minutes of the engine running the car began to warm up gently and eventually the window inside was clear and the glass warm enough to use the wipers to clear the melting frost. This created a slush on the edge of the wiper range that thanks to the windows protective layer applied days before ran down and cleared without problems.
Overall score: 3
One of the most popular methods in winter is the use of de-icer or similar products, averaging £3 a can or bottle, some choose to make their own with rubbing alcohol and water in a two parts alcohol to one part water. De-icer, as seen in the video, took a few minutes, turning the snow and frost to slush, it also left the inside of the window misty as well as a streaky finish that obstructed the view slightly. De-icer certainly has its place and is vital when other methods aren't available.
Overall score: 4
Winter requires most to dig out the ice scraper or use the store card that has never left their purse or wallet. A risk when using a scraper is pushing a stone or part of the tool rubbing against the glass surface and causing damage. Other winter car care tools include a soft bristle brush, perfect for pushing snow off the roof, bonnet and windows of a car. Although the scraper allows you to keep the car locked and secure as well as clearing all windows it does risk damage and doesn't clear the mist of the inside of the windows or warm up the car.
Overall score: 6
Standard technology for rear windows for many years, heated glass takes some time and doesn't clear the exterior alone, once the glass is heated windscreen wipers are required to fully clear the window. Heated windscreens are available from manufacturers such as Ford, Land Rover, Vauxhall and Volvo. Thin wires run through the glass to not restrict view. When tested on a Ford Fiesta, at -4 degrees Celsius both front and rear windows were defrosting in just 2 minutes and fully cleared with help from the wipers in an additional 30 seconds. For the car to draw the most power the engine must be running which requires the driver to attend the vehicle at all times.
Overall score: 8
The fastest, cheapest and most effective way to remove morning or evening frost from all of your car is warm water, it is important to note that boiling water from a pan or kettle is ill-advised as well as using water at scalding temperatures. We found that recycling an old 5-litre windscreen wash bottle or 2-litre drink bottle was best, containing enough water to clear a car. Pouring the water firstly on the roof or body panels allowing it to run down the windows quickly defrosted the glass as well as gently warming it preventing condensation on the inside, the water was warm enough to clear the ice from the lights as it ran down, pouring over the windscreen jets can also unblock the nozzles. In temperatures seen in the UK warm or hot water is suitable for up to about minus fifteen. Although puddles can freeze beneath the car, most will clear before the driver parks again. Windscreen wipers or a microfiber cloth can be used to dry any standing water. See our evidence in our video below.
Overall score: 9
There is a popular myth that suggests using a half onion and rubbing it on the surface of the glass will leave a film on the window that will prevent moisture and frost from forming on the window and prevent freezing.
Result - We tried the onion trick and we didn't notice any prevention of frost. Whether it is the chemical used that causes rain to bead up on the windscreen but the onion left a residue that proved stubborn at -3 degrees to remove even with some soap and water.
Another odd suggestion for our list is using toothpaste, although enamel protection and mint fresh flavours do nothing for a car's wing mirrors or windows we did notice that apart from a cool mint scent windows didn't seem as frozen as other parts of the car. Although frost still formed the defrosting seemed faster and although there was some blurring from the treated area the majority was clear and easy to remove.
Now the theory is sound with this one, put something warm either on or near the frozen panel or glass pane and let the radiating heat melt the ice and remove condensation, a sealed freezer bag with warm water was reasonably quick at clearing the windows leaving no mess or water to freeze on the ground. Similarly hot water bottles release less heat but maintain their warm for longer and so we only needed one to defrost the hatchback, however, it wasnâ€™t time efficient. Using a hot water bottle or a securely sealed bag of warm water takes some time but is handy if you have a busy morning routine and can be left to defrost the car with the doors locked.
As covered in our how to prepare your car for winter blog, using a towel or other material stretched across the windscreen can simply serve to reduce freezing, this doesn't help with the rest of the car windows. Specifically designed windscreen cover can prevent significant freezing or light frost on the glass, while full body car covers can be a godsend in heavy snow drifts to speed up the clearing of a car, they typically don't offer much protection from freezing temperatures and can cause more harm than good to paintwork in high winds if not properly secured.