Fuel Economy in Cold Weather &Hot Weather

Fuel Economy in Cold Weather
Cold weather and winter driving conditions can

reduce your fuel economy significantly.
Fuel economy tests show that, in short-trip city 
driving, a conventional gasoline car's gas mileage is 
about 12% lower at 20°F than it would be at 77°F. It 
can drop as much as 22% for very short trips (3 to 4 
miles).
The effect on hybrids is worse. Their fuel economy can
drop about 31% to 34% under these conditions.

Why is winter fuel economy lower?

Cold weather affects your vehicle in more ways than you might expect:

• Engine and transmission friction increases 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.

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 I do to improve my fuel economy in cold weather?

You may not be able to completely mitigate cold weather's effect on your fuel economy, but you can do some simple things to help your gas mileage:

• 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.
• 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.

Fuel Economy in Hot Weather

Hot weather can actually increase your fuel economy.

Your engine warms up to an efficient temperature

faster; summer grades of gasoline can have slightly

more energy; and warm air causes less aerodynamic 

drag than cold air.

However, keeping passengers comfortable in hot

weather by rolling down the windows or using the air

conditioning (AC) can reduce fuel economy.

Running your car's air conditioning is the main 

contributor to reduced fuel economy in hot 

weather. Its effect depends on a number of factors,

such as the outside temperature, humidity, and intensity of the sun. Under very hot conditions, AC use can reduce a conventional vehicle's fuel economy by more than 25%.1,2 The AC's effect on hybrids, plug-in hybrids, and electric vehicles (EVs) can be even larger on a percentage basis.2

Driving with your windows down can also reduce fuel economy. Open windows increase aerodynamic drag (wind resistance), making your vehicle use more energy to push through the air. This effect is quite small at low speeds but increases at highway speeds.1,3

What can I do to improve my fuel economy in hot weather?

• Roll the windows down at lower speeds; use the 
  

        AC at highway speeds.

• Don't use the AC more than needed or set thetemperature lower than needed.

• Park in the shade or use a sunshade so that the cabin doesn't get as hot.

• Drive with the windows open for a short time before using the AC. Letting hot air out of the cabin first will put less demand on the AC and help your vehicle cool faster.

• Don't idle with the AC running before driving. Turn the AC on after you begin to drive or after airing out the cabin briefly. Most AC systems will cool the vehicle faster while driving.

• Read your owner's manual. Most manuals explain how the AC system controls work and how to best use and maintain the AC system.4
• For plug-in hybrids and electric vehicles, pre-cooling the cabin while plugged into the charger can extend your vehicle's range. Also, using a warmer temperature setting for the AC will use less battery power.

From Data Sources.....http://www.fueleconomy.gov/feg/coldweather.shtml