Cold Weather Driving: the Windshield

One of the challenges we winter drivers face in keeping fuel economy from dropping too much is dealing with windshield ice and fog. It is easy to defrost and pre-heat the car for 10-20 minutes before driving, but fuel economy will take a major hit unless the drive is quite long.

I describe below my recipe for a clear windshield using minimal energy. Keep in mind that this is for a cold, high desert climate. High humidity requires a different approach. First things first, have excellent windshield wipers. I have learned to put on a new set every winter season. Next requirement is to use the winter formulation of windshield wiper fluid. It has to flow!

• I start the defrost about 1 minute before I drive off. Depending how much time I expect to spend scraping the windows may mean I start the car and hit the defrost button before I start scraping, or I scrape the windows first.
• I scrape the windshield well, and try to remove the loose ice. I also gently clean the wiper blades.
• Back in the car, I run the wipers with a generous amount of fluid and clean the glass. The wiper fluid does not fog up because the glass is warm enough from the defroster. Good blades remove almost all the fluid, and the small amount that remains quickly evaporates.
• Now I can turn off the defroster, and the glass stays clear. All told, it has been on some 2-3 minutes.
• Five - 10 minutes into driving I turn on the cabin heat.

I'm not sure how much power the front windshield defroster draws, but even at 2 kW the use for three minutes amounts to 100 Wh. Over a 10 mile drive that takes 20 minutes, the winter fuel economy hit unrelated to ICE warm-up is reduced to under 5%.

 

Yep, car lives outside. During the winter AM temps are 0 - 30F, and most often in the low 20s F.
We do not get a lot of snow; mostly I have to deal with frost.

 

Absolutely. We have micro-climates every 15 miles around here. An hour drive away, the ski resort Telluride might as well be in the Swiss Alps.