January 6, 2009
Contrary to common belief, wind chill does not affect cars the way it does humans. Click image to enlarge
By Paul Williams; photo by Chris Chase
Ottawa, Ontario – According to a recent Ottawa weather forecast, “Today the temperature will drop to minus 10 degrees, but with the wind chill factor, it will feel like minus 19.”
So, is it minus 10 or minus 19? Or are they just saying “minus 19″ to make it sound more dramatic? After all, in the summer we’re told the daytime high will be 27, for example, but with the relative humidity, it’ll “feel like” 35.
No, it turns out that the wind chill factor is a serious concern, and there’s a good reason for including it in the winter weather forecast, which I’ll get to shortly. But here’s a question: If it’s going to “feel like” minus 19 (or minus 37 for that matter), will this affect your car? In other words, is it harder for your car to start in weather that feels colder because of the wind chill factor?
To answer that, you need to understand that wind doesn’t actually affect the air temperature, but it does affect warm surfaces like exposed skin. The wind will make you feel colder by accelerating the pace that heat is removed from the skin surface (by convection). Most importantly for Canadians — and the reason the wind chill factor is broadcast during the winter months — is that wind chill will also accelerate the onset of frostbite.
For instance, Environment Canada indicates that with a wind chill between the freezing point (0 degrees Celsius) and minus 27, the risk of frostbite is low. But a wind chill factor between minus 28 and minus 39 will cause exposed skin to begin freezing in as little as 10 minutes. And at minus 40, you’re in a high risk situation, with exposed skin beginning to freeze in only five minutes. For a more detailed wind chill chart, go to Environment Canada’s page on wind chill and its effects.
But what about your car? Is it affected by the wind chill factor? Well, cars aren’t susceptible to frostbite, so in everyday driving, the answer is no. If you measure the temperature of the cold engine block or battery of a vehicle in your driveway, you’ll see they are the same as the ambient temperature, regardless of the wind.
However, there is a wrinkle to this observation. Wind chill will affect the pace at which an exposed engine cools. So, if you stop your car and open the hood, the engine will lose its heat more quickly if it’s windy. Similarly, if your radiator is exposed to the wind on a cold day, it could take a little longer for your car to reach its operating temperature.
But as far as starting your vehicle is concerned, the wind chill factor has no impact at all.