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Fuel Economy

Posted on February 10, 2022.

AAA recently evaluated thousands of vehicles by comparing their Environmental Protection Agency fuel economy ratings with actual owner-reported gas mileage as listed on the EPA’s website. Interestingly, 81.8 percent of drivers reported getting better fuel economy than the EPA estimates, although 16 percent of motorists reported their fuel economy was lower than the EPA ratings.

AAA also identified certain types of vehicles that were reported to have fuel economy that was consistently better or worse than the EPA ratings. For example, drivers of vehicles with diesel engines averaged 20 percent better mileage than the EPA ratings. But while minivan owners reported gas mileage at or above the EPA ratings, real-world numbers were at the lower end of the fuel efficiency scale compared to other vehicle categories.

Understanding Fuel-economy Labels

Getting the best possible driving mileage is one way drivers combat high fuel costs. When prices near the $4 per gallon mark, the number of miles covered per gallon of fuel has taken on new importance with consumers. A clear understanding of how the ratings are established and what you can learn from the window sticker will help you make educated driving decisions.

The Testing Procedure

The Environmental Protection Agency governs the fuel-economy ratings that are listed on a vehicle window sticker. Well-defined tests are used to establish fuel mileage, using a computer-controlled chassis dynamometer to replicate the driving experience.

The basis for EPA ratings were the “city” and “highway’ driving cycles. These tests are intended to mimic the basic commute drivers experience daily. The EPA testing results in an average speed of 21 mph for the city test and 48 mph for the highway test.

Based in large part on scientific input from the Auto Club of Southern California’s Automotive Research Center, the EPA adopted new, more accurate methods for estimating the fuel economy ratings that were implemented in 2008. Three additional tests were added to the EPA’s protocol to add a more real-world scenario into these tests:

  • A “high-speed” test includes more rapid acceleration and a top speed of 80 mph. This is closer to a modern day drive on an interstate highway.
  • The “air conditioning” test is performed in a climate-controlled chamber with the temperature kept at a steady 95°F. The vehicle’s air conditioning system is on during the test.
  • The “cold” test is run in a climate-controlled chamber at 20°F.

The results of these tests are used to populate the information you see on the fuel-economy window label.

The Testing Team

The information on the window sticker likely came from the automaker’s tests of the vehicle. Every manufacturer supplies mileage rating information to the EPA, and they are expected to follow the Federal Test Protocol detailed in the Code of Federal Regulations.

The EPA conducts original tests on about 250 vehicles a year. About 75 percent of the EPA’s tests are random checks of the manufacturer’s results. The EPA also conducts tests that address consumer reports of fuel economy inconsistent with the stated ratings.

Check the Window Sticker

The fuel-economy labels on new vehicles are regulated by the EPA and the National Highway Traffic Safety Administration (NHTSA). Estimated mileage ratings are powerful tools to help motorists make educated decisions that reduce the cost of vehicle ownership. The labels provide important information about the vehicle’s fuel economy, including:

  • Estimates on how much consumers will save or spend on fuel over the next five years compared to the average new vehicle.
  • Comparing energy use and costs between vehicles that use alternative fuels and conventional gasoline-powered vehicles.
  • An estimate of how much fuel or electricity it takes to drive 100 miles.
  • A QR Code® that directs you to online information comparing various models on fuel economy and other environmental and energy factors.

The information allows consumers to compare vehicles in all classes and can help shoppers find the most efficient vehicle that fit their needs.

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Keeping Your Vehicle in Shape

Posted on February 10, 2022.

Keep Your Engine Properly Tuned

Fixing a car that is noticeably out of tune or has failed an emissions test can improve its gas mileage by an average of 4%, though results vary based on the kind of repair and how well it is done.

Fixing a serious maintenance problem, such as a faulty oxygen sensor, can improve your mileage by as much as 40%.

Fuel Economy Benefit: 4%
Equivalent Gasoline Savings: $0.13/gallon

Keep Tires Properly Inflated

You can improve your gas mileage by 0.6% on average—up to 3% in some cases—by keeping your tires inflated to the proper pressure. Under-inflated tires can lower gas mileage by about 0.2% for every 1 psi drop in the average pressure of all tires. Properly inflated tires are safer and last longer.

The proper tire pressure for your vehicle is usually found on a sticker in the driver's side door jamb or the glove box and in your owner's manual. Do not use the maximum pressure printed on the tire's sidewall.

Fuel Economy Benefit: 0.6%
Equivalent Gasoline Savings: $0.02/gallon

Use the Recommended Grade of Motor Oil

You can improve your gas mileage by 1%–2% by using the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1%–2%. Using 5W-30 in an engine designed for 5W-20 can lower your gas mileage by 1%–1.5%. Also, look for motor oil that says "Energy Conserving" on the API performance symbol to be sure it contains friction-reducing additives.

Fuel Economy Benefit: 1%–2%
Equivalent Gasoline Savings: $0.03–$0.07/gallon

Replacing a Clogged Air Filter on Modern Cars Improves Performance but Not MPG

Replacing a clogged air filter on vehicles with fuel-injected, computer-controlled gasoline engines—such as those manufactured from the early 1980s to the present—or diesel engines does not improve fuel economy, but it can improve acceleration.

Replacing a clogged air filter on an older vehicle with a carbureted engine can improve both fuel economy and acceleration by a few percent under normal replacement conditions.

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