What this means in practical terms is that if the antifreeze in your car's radiator is good to 10 degrees Fahrenheit and the temperature drops to 20 Fahrenheit you don't have to worry, even if your car is out in a 20 mph wind that drops the wind chill to minus 10 degrees. As long as the actual temperature is 10 degrees, the fluid in your car's radiator and engine block will not cool below 10 degrees no matter how hard the wind blows. You could leave the car's hood open and it wouldn't make any difference. The only difference is that the fluid in you car's cooling system will cool to the 10-degree air temperature quicker on the windy night than on a calm night. But it won't drop below the actual temperature.
Some scientists have doubts about the ways in which wind chill is used.