The worst drop came from battery-based vehicles, which saw their typical mileage drop by between 31 percent and 34 percent. That means a 45 mpg model such as a Ford Fusion Hybrid might deliver only 30 mpg when the temperature plunges.
But even a gas-powered car that normally gets 30 mpg might struggle to deliver 24 mpg during short trips, when mileage drops the most, according to the Oak Ridge researchers.
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Lower temperatures are just one of the reasons for reduced fuel economy. The lab pointed to other factors, including:
- Icy or snow-covered roads, which can decrease traction. Fuel is wasted when the car is literally spinning its wheels.
- Slowing down on slick roads, as vehicles are typically designed to deliver their best mileage at highway speeds.
- Operating in four- or all-wheel-drive.
- Thicker oil and other vehicle fluids, which increase internal friction and the time it takes a car to reach optimum operating temperature.
- Using more energy to power blower fans, defrosters and seat heaters.
- Winter gasoline blends, which tend to have lower levels of energy per gallon than summer blends.
- Letting a vehicle idle—getting zero mpg—to warm it up.
Then there's the battery. Even in a conventional vehicle, it's likely to be less efficient when it gets cold, requiring the alternator to run more frequently. And in a hybrid, plug-in or electric vehicle, a cold battery will hold less energy, limiting both range and energy efficiency.
(Read more: Tesla cars are worth more used than new)
According to Oak Ridge research, drivers can take a number of steps to improve their mileage during the winter. For example, park the car where it can stay warm and combine trips rather than make a lot of short ones, so the engine and fluids are fully warmed up.
Other mileage-friendly suggestions include:
- Using the oil the manufacturer recommends for winter.
- Limiting the amount of time spent warming the vehicle up, as it will actually heat up faster while driving.
- Checking the tire pressure frequently. This falls as temperatures drop, tires aren't as energy efficient when they're low and may not get an adequate grip.
For a plug-based vehicle, such as a Chevrolet Volt or a Toyota RAV4 EV, preheat the cabin, Oak Ridge researchers said. That way the car warms up while it's plugged in rather than while it's being driven.
—By CNBC Contributor Paul A. Eisenstein. Follow him on Twitter @DetroitBureau or at thedetroitbureau.com.