Winter weather brings a variety of driving challenges, but one that most people don’t think about is a drop in fuel economy for their gasoline-powered car and a reduction of range for their electric vehicle (EV). Tests by the US Department of Transportation (DOT) have shown that cars with gasoline engines can expect a reduction of fuel economy of 15% when the temperature drops from 77°F to 20°F. It can drop as much as 24% for short (3- to 4-mile) trips.
For EVs, the effects are larger. Range can drop roughly 40% in mixed city and highway driving with about two-thirds of the extra energy consumed being used to heat the cabin. For hybrids, including plug-in hybrids, cold weather fuel economy typically decreases by 20% to 40% in city driving and 25% to 45% on short trips.
Why the Drop?
According to the DOT, cold weather affects your vehicle in more ways than you might expect:
- Engine and transmission friction increase in cold temperatures due to cold engine oil and other drive-line fluids.
- It takes longer for your engine to reach its most fuel-efficient temperature. This affects shorter trips more since your car spends more of your trip at less-than-optimal temperatures.
- Heated seats, window defrosters, and heater fans use additional power.
- Warming up your vehicle before you start your trip lowers your fuel economy—idling gets 0 miles per gallon.
- Colder air is denser, increasing aerodynamic drag on your vehicle, especially at highway speeds.
- Tire pressure decreases in colder temperatures, increasing rolling resistance.
- Winter grades of gasoline can have slightly less energy per gallon than summer blends.
- Battery performance decreases in cold weather, making it harder for your alternator to keep your battery charged. This also affects the performance of the regenerative braking system on hybrids, plug-in hybrids, and electric vehicles.
- In severe winter weather, your mpg can drop even further.
- Icy or snow-covered roads decrease your tires' grip on the road, wasting energy.
- Safe driving speeds on slick roads can be much lower than normal, further reducing fuel economy, especially at speeds below 30 to 40 mph.
- Using four-wheel drive uses more fuel.
What Can You Do?
There are some simple things that you can do to reduce the effect of cold weather on fuel economy and EV range. According to the DOT:
- Park your car in a warmer place, such as your garage, to increase the initial temperature of your engine and cabin.
- Combine trips when possible so that you drive less often with a cold engine.
- Minimize idling your car to warm it up. Most manufacturers recommend driving off gently after about 30 seconds. The engine will warm up faster being driven, which will allow the heat to turn on sooner, decrease your fuel costs, and reduce emissions.
- Don't use seat warmers or defrosters more than necessary (Especially in an EV)
- Check your tire pressure regularly.
- Use the type of oil recommended by your manufacturer for cold weather driving.
- Remove accessories that increase wind resistance, like roof racks, when not in use.
- If you drive a plug-in hybrid or electric vehicle, preheating the cabin while plugged into the charger can extend your vehicle's range.
- If you drive a plug-in hybrid or electric vehicle, using the seat warmers instead of the cabin heater can save energy and extend range.
Longer Charging Time
Cold batteries don’t accept electrical energy as quickly as warm batteries do. This means that your EV will take longer to charge, especially if it is charging outdoors at sub-freezing temperatures. A few EVs have thermal management systems that warm the battery during charging, but because some of the charging energy goes not this warming process, it can also increase charging time over what you might expect on a warm day.
Kevin Clemens is an engineering consultant who has worked on automotive and environmental projects for more than 40 years.