Winter Driving and Gas Mileage

I rolled over in bed this morning, looked out the window, and saw an army of snowflakes descending upon my house and yard. On 20 degree days like this, my joints ache, and it’s hard to move. I’m probably running at about 80 percent efficiency. Should I expect more from my hybrid?

All vehicles, machines, and people—not just hybrid cars—get less mileage to the gallon on cold winter days. By most accounts, the drop-off in efficiency is somewhere between 10 and 20 percent. If you’re driving a 15 mpg SUV, you might not notice the drop to 13 mpg. But, if you’ve come to expect 50 mpg from your Prius, and you paid the premium to reach that level, then the drop to the low-40s will seem much more dramatic.

What causes the decrease in fuel economy during the winter?

  • Engines take longer to warm up. During this time, they are running heavy at high RPMs. Even after you get going, all the car’s systems have to work harder to maintain a normal operating temperature.
  • Nobody likes to step into a cold car. Do you ever start the car up and leave it running for a few minutes while you go inside and slug down the second or third cup of coffee? Is the car running while you’re chipping away at the ice on the windshield? All of this burns gas and reduces your overall fuel economy numbers.
  • The air is denser when it’s cold. It’s likely to be windy in the winter. The roads can be covered in snow and ice. This all adds up to more resistance.
  • Tires are stiffer. Until they warm up on the highway, they roll less easily. And the tire pressure is likely to fall below the desired range.
  • In the winter, you use your headlights, defrosters, and heaters more. To make matters worse for Honda hybrids, the use of the defroster and heater will reduce how often the idle-stop feature kicks in. (The Honda Civic Hybrid manual says that auto-stop will not function below 32 degrees Fahrenheit.) The ability for hybrids to go all-electric during idle is essential to its fuel parsimony strategy.
  • Winter-blend gasoline is cut with various additives, such as anti-gel agents. As a result, there’s less tiger in the tank.

Can you do anything to steal back a few mpgs from Old Man Winter? Yes. The same things you should be doing all year round. Combine shorter trips into longer ones. Keep your car maintained and your tire pressure up. Don’t speed. If you can, don’t drive until the road is clear and the day warms up a bit.

Also, try to drive less. Tell your boss it’s too cold and stay inside where it’s warm and toasty. Who wants to go outside in the cold anyhow?