It was a long, cold winter for much of the U.S., and if you live in one of those Snowbelt states you might have noticed that your fuel bills rose whenever the mercury sank, as your car worked longer and harder to get both the engine and passenger compartment up to temperature. The good news is that hot weather actually can reduce your fuel consumption — at least if you follow some basic tips. And that's even more important with gas prices unexpectedly rising.
While your engine warms up faster — requiring less fuel — you need to think about ways to keep the passenger compartment cool without putting the air conditioning on full blast, cautions the Department of Energy and other automotive experts.
“Under very hot conditions, AC can reduce a conventional vehicle’s fuel economy by more than 25 percent,” according to new guidelines posted on Fueleconomy.gov. And the impact of running your air conditioning in a hybrid, plug-in or battery-electric vehicle “can be even larger on a percentage basis,” it notes.
In the days before AC became pretty much standard across the board, you’d likely keep your windows open while driving on a hot day. But that isn’t a good way to cut down on the cost of running your car’s AC, experts note. Today’s vehicles are designed to maximize aerodynamics — to minimize drag. This might not matter when you’re cruising around town at low speeds, but wind resistance increases exponentially when you get on the highway, and the added drag of leaving your window open is likely to use more fuel than running your AC.
That said, the DoE says opening your windows to let out excess heat when you start your car on a hot day is more efficient than trying to cool down what is essentially a greenhouse. Start the AC after you get the engine running and have aired out the cabin. Air conditioning usually is more effective and efficient when you are moving.
Other recommendations from the DoE and other sources:
- Get a summer service check to make sure your car is in tune. It uses less fuel when it’s running efficiently;
- Make sure the AC system is checked and has the proper level of coolant to run most efficiently. Also make sure your radiator has enough antifreeze which, in summer, helps prevent boilover;
- When you park, look for a spot in the shade, or get a sunshade that can reflect or block the sun’s rays.
- Drive at or under the speed limit to save as much as 33 percent of your fuel. Coasting to a stop and starting out smoothly also can reduce your bills.
- Make sure tires are at the recommended pressure. It's best to check in the morning before temperatures rise and pressures increase.
If you own a plug-based vehicle, such as a Nissan Leaf or Chevrolet Volt, chances are you can pre-cool the cabin (and pre-heat it during the winter) while it’s still connected to its charger. That not only means it will be pleasant to climb into but that you’ll also maximize range.
“Also, using a warmer temperature setting for the AC will use less battery power,” notes the Fueleconomy.gov page.
And, of course, it pays to compare fuel prices. Warehouse clubs and grocery stores often have some of the best prices.
One folk tale that apparently doesn’t make a difference concerns the time of day when you fill up. Like other liquids, gasoline expands as it warms, but service stations normally store their fuel underground, where temperatures vary only slightly, so you won’t get more gas for your money in the cool of the morning.
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