Key takeaways
- The US Department of Energy’s FuelEconomy.gov says aggressive driving can lower gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic.
- Using premium fuel in a car that doesn’t require it will “probably” give no benefit, according to the DOE. Warming your car up by idling isn’t needed either.
- Idling can use a quarter to a half gallon of fuel per hour, and restarting takes about 10 seconds’ worth of fuel.
- The government’s mpg estimates are for comparing vehicles, not a guarantee of what you’ll get.
This article is general information based on US Department of Energy and EPA material. Check your owner’s manual for advice specific to your vehicle.
Myth 1: “Premium gas improves fuel economy”
Fact (DOE): “Unless your vehicle was specifically designed for premium fuel or knocks severely with regular fuel, you will probably experience no benefit from using premium fuel over regular under normal conditions.” Under severe duty such as towing or hauling heavy loads, especially in hot weather, higher-octane fuel “might improve performance and gas mileage and reduce carbon dioxide emissions by a few percent.” The DOE says to check your owner’s manual to see whether premium is recommended and under what conditions.
Myth 2: “Your car needs to warm up before you drive”
Fact: “Modern vehicles can be driven within seconds of being started, though the engine should not be subjected to extreme loads until it has reached its normal operating temperature.” The DOE adds that “the quickest way to warm up a vehicle’s engine is to drive it.” In its cold-weather advice, it says most manufacturers recommend driving off gently after about 30 seconds, and that “warming up your vehicle before you start your trip lowers your fuel economy. Idling gets 0 miles per gallon.”
Myth 3: “It takes more fuel to restart a car than to let it idle”
Fact: “Modern fuel-injected engines start very efficiently, especially when warmed up.” Idling “can use a quarter to a half gallon of fuel per hour, depending on your vehicle’s engine size,” costing “about 1 to 2 cents per minute.” The DOE says it takes only about 10 seconds’ worth of fuel to restart a vehicle, and suggests turning your engine off when your vehicle is parked, except when you’re waiting in traffic or in a line where you would need to turn it on and off frequently. Its best practices: limit engine starts to about 10 a day on average (unless you have a start-stop system), and any shutdown longer than 1 minute will save money.
Myth 4: “Replacing your air filter will improve fuel economy”
Fact: This is true for older carbureted engines, but “modern fuel-injected engines have on-board computers that automatically adjust the fuel-air ratio to the proper level.” Changing a dirty air filter “won’t increase your fuel economy, but it might improve your engine’s performance.”
Myth 5: “Additives and gadgets can dramatically improve fuel economy”
Fact: Apart from full conversions that meet all EPA certification standards, “tests have shown that such devices and additives do not improve fuel economy and may damage your engine and/or increase your tailpipe emissions.”
Myth 6: “An older car always gets much worse mileage”
Fact: “A vehicle that is properly maintained will retain its efficiency for many years.” The DOE says vehicles that are 10 or even 15 years old “will experience little decrease in fuel economy if properly maintained.”
Myth 7: “You have to drive a small car for good mileage” and “manuals always beat automatics”
Fact: Advanced technologies “are allowing standard-sized vehicles to be very fuel efficient.” And automatic transmissions have improved so much that the automatic version “often gets the same or better fuel economy” than the manual. You can compare models on FuelEconomy.gov’s Find a Car tool.
Myth 8: “The EPA mpg number is a guarantee”
Fact: “The primary purpose of EPA fuel economy estimates is to provide consumers with a uniform, unbiased way of comparing the relative efficiency of vehicles.” No single test “can accurately model all driving styles and environments.” Different fuel blends also matter: gasoline with 10% ethanol “can decrease fuel economy by about 3%.”
What actually helps
The DOE’s “Driving More Efficiently” page lists:
- Drive sensibly. Aggressive driving (speeding, rapid acceleration and braking) “wastes gas.” It can lower mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic. Sensible driving is also safer.
- Observe the speed limit. Each vehicle has its own best speed, but “gas mileage usually decreases rapidly at speeds above 50 mph.” The DOE says each 5 mph you drive over 50 mph is like paying an additional $0.28 per gallon for gas (at its assumed fuel price).
- Remove excess weight. An extra 100 pounds could reduce mileage by about 1%, and the effect is bigger on smaller vehicles.
- Avoid excessive idling. See Myth 3.
- Use cruise control on the highway. It helps you keep a constant speed and, in most cases, saves gas.
- Consider a driver feedback device. A study cited by the DOE found they can help the average driver improve fuel economy by about 3%, and by about 10% for those using them to save fuel.
For winter, see our guide to why electric car range drops in cold weather, which also covers the DOE’s cold-weather figures for gas cars. And for tires, see our guide to tire pressure and the TPMS warning light.
Quick checklist
- Use the fuel grade your owner’s manual says. Premium only if required or recommended
- Drive off gently instead of idling to warm up
- Turn off the engine if you’ll be stopped for more than a minute (not in traffic)
- Ease off the throttle and brake smoothly
- Stay at or below the speed limit, and mind speeds over 50 mph
- Take heavy items out of the car
- Use cruise control on highways
Frequently asked questions
Does premium gas give better mileage? Probably not, unless your car is designed for it, according to the DOE.
Do I need to warm up my car? The DOE says modern cars can be driven within seconds, and driving is the quickest way to warm the engine.
Does turning the engine off save fuel? Yes. Idling can use a quarter to a half gallon an hour, and restarting takes about 10 seconds of fuel.
Why is my mpg lower than the sticker? EPA estimates are for comparing vehicles. Driving style, fuel blend and conditions all change your result.
Information checked on: November 13, 2026. DOE figures are updated periodically.
Sources
- US Department of Energy and EPA, FuelEconomy.gov, “Fuel Economy Myths and Misconceptions” (fueleconomy.gov/feg/myths.shtml)
- US Department of Energy and EPA, FuelEconomy.gov, “Gas Mileage Tips: Driving More Efficiently” (fueleconomy.gov/feg/driveHabits.jsp)
- US Department of Energy and EPA, FuelEconomy.gov, “Fuel Economy in Cold Weather” (fueleconomy.gov/feg/coldweather.shtml)
