Fuel Economy Myths

Remember when you were a kid and your parents took you shopping for back-to-school clothes? Included on the list was probably a new pair of sneakers. The best way to tell if the shoes were any good was for you to run around the store to see if they made you faster.

Of course the shoes that made you run the fastest were the ones you wanted. However, it’s a myth that one sneaker will make you faster than another.

The same is true for cars. We’re raised with some crazy myths. Many of them have been handed down from previous generations, and have dubious accuracy. Others are doled out in casual conversation, but are accepted as facts.

Below are some fuel economy myths that may burst your bubble:

Topping off your car

At one time or another we’ve all stood at the gas pump as the nozzle turns itself off. You grab the handle to try and squeeze every last drop into your tank. Filling your tank to its maximum capacity is a good thing, right? Nope.

The gas pump nozzle is designed to stop when the tank is full. By trying to pump more gas into your car after it’s full, you’re actually pushing gas back into the evaporation system - mainly the evaporation canister - which can ruin it and the evaporation system. Topping off fuel is the number one cause of the failure of the canister, and can be costly to repair.

Clean air filters

Most people think that a dirty air filter will kill gas mileage. The reality, however, is that’s not true. According to FuelEconomy.gov, a dirty air filter has minimal effect on gas mileage in late model cars. A well-maintained fuel-injected engine will still deliver expected fuel economy regardless of how dirty the air filter is.

Late model cars with fuel-injection engines have onboard computers which calculate the amount of air taken into the engine, and adjusts the fuel flow accordingly. The cleanliness of the air filter isn’t part of the equation. That doesn’t mean that you shouldn’t swap out your dirty filter for a new one. It’s a good habit to replace your air filter when it’s dirty.

Older cars, those made before 1980, are an exception to this rule. In those cars, a dirty air filter adversely affected the performance and gas milage.


It’s logical to think that maintaining a consistent speed will save fuel, and there’s no better way to maintain a steady speed than with cruise control. If you’re driving on a flat stretch of highway this is true, but highways are rarely flat. When your cruise control system senses an incline it accelerates to maintain your desired speed. The rate of acceleration could be more rapid than how you would accelerate on your own.

Quick acceleration kills your mileage, so take control of your vehicle when you see undulations in the road, accelerate gradually, and then turn the cruise control back on when the road flattens out.

The sensors will tell you when to check your tires

When was the last time you checked your tire pressure? Possibly the last time the low pressure sensor went off? Maybe you can’t even remember. According to the National Highway Traffic Safety Administration, one-third of all car tires are underinflated. If tire pressure is too low, tires can overheat, cause excess friction with the road, wear prematurely, and worse, lead to blowouts. Check your tire pressure once a month. The recommended tire pressure is either inside your gas filler door or in the glove compartment. It’s important to remember that you have to check the pressure for five tires, not four: don’t forget your spare.

Don’t drag behind

Anyone who has watched the Tour de France knows that pedaling behind another rider cuts wind drag. It stands to reason that if you drive behind a truck (or a car that’s bigger than yours) it will shield you from the wind, thus improving your gas mileage. Based on pure physics, this theory is true. However, tailing a truck to improve your gas mileage is a really bad idea. The extra efficiency you might gain isn’t worth the risk of an accident.

Premium gas will help boost mileage

Your car is tuned to run on a specific octane of gas. If you’re using premium grade in an engine that is meant to run on regular, you could be pouring money down the drain. If you’re unsure, Edmunds suggests running your own test. Fill your tank completely with regular gas twice. Then fill your car completely twice with premium. Record your mileage, and gallons used. Pay attention to your fuel economy and performance. If regular gas is recommended for your car and you fill it with premium, the chances are you won’t see much improvement.

However, if your car is rated for premium, and you fill it with regular you could see a drop off in performance from anywhere between 6 to 10 percent according to a test by Car and Driver.

Go small or stay home

Common sense would dictate that small cars, such as a Mini Cooper, would rock the world when it comes to miles per gallon. Edmunds tested the car under both city and highway conditions, and the five-seat Mini (who knew it could seat five?) earned 29 mpg in city driving and 40 mpg on the open road. Respectable numbers to be sure.

But not all fuel efficient cars need to be miniature size. The Toyota Prius V, a larger 5-seat hybrid station wagon, gets an even better 44 mpg city/40 mpg highway.

As the Mini and Prius V show, it’s not the size of the car that matters – it’s what’s under the hood. It used to be that only smallish cars came with fuel efficient hybrid engines. More and more standard-size vehicles, SUVs, and high performance sports cars utilize technology with hybrid drivetrains, diesel engines, turbochargers, and low-rolling resistance tires. These advancements allow many new medium and large cars to have better fuel economy than ever before.

Manual transmissions get better mileage

A 2013 report by Edmunds busted another mileage myth. For years it was believed that manual transmission cars got better mileage than their automatic counterparts. "Not true," says Edmunds.

The number of manual transmission cars sold each year varies between 3.9 percent (Edmunds) and 10 percent (Fox News). Regardless of which automatic you pick for a head-to-head test, both the manual and automatic cars will get about the same mileage.

Edmunds compared both manual and automatic transmission versions of the Chevy Cruze Eco and Ford Focus. The Chevy manual transmission clocked in at a combined (the average between city and highway driving) 33 mpg, and 31 for the automatic. The Focus six-speed got 30 mpg combined compared with the automatic version at 31 mpg.

The improvement in gas mileage for automatic cars is due to advancements in technology, and a gain in additional transmission gears – some new automatic transmissions have as many as 10 gears!

The fuel efficiency performance gap between automatic and manual transmission vehicles is now virtually non-existent.

High performance means bad mileage

Baby boomers were raised to believe that if you wanted to drive a high performance sports car, you’d have to live with lousy gas mileage. In their experience, this was true. The classic 1965 Ford Mustang Fastback, for example, topped out at about 14 mpg.

Remember the Firebird from the Rockford files? It got between 10 and 14 mpg. Both cars had performance, but at a price.

Tesla shattered the myth that super high performance cars could also be economical. The company builds an all-electric car that can go from zero to 60 in under four seconds, and gets 265 miles on a single charge. The downside of the Tesla is its price.

Fortunately for consumers, there’s now a middle ground. Most major car manufacturers offer cars that look sporty, offer superior performance, have plenty of cargo room, and get nearly 30 mpg combined gas mileage, all at modest prices.

Cars are fuel efficient forever

A car’s engine is at peak efficiency a few thousand miles into its lifespan. Over the years a car’s efficiency, through increased friction, internal engine wear, seals, aging components, bearings wearing out etc. take its toll and the engine doesn’t run as well. You can do your best to maintain your car with regular tune-ups, but it will never be brand new again. Generally, when you get a new car your miles per gallon will be consistent for a time, and then begin to trend down slowly. This is normal and to be expected.

What does the future hold?

In 2012 the Obama Administration announced new standards for fuel efficiency. The administration called for cars and light duty trucks reach the equivalent of 54.5 mpg by 2025. The increase in gas efficiency is expected to save motorists more than $1.7 trillion in fuel prices, and oil consumption will be reduced by 12 billion barrels annually.

Thirteen major car manufacturers and the United Auto Workers Union pledged to work together to build more efficient autos that reduce greenhouse gas emissions.

Within the next decade, electric vehicles, hybrids, and clean cars will be the norm, and we may all be driving cars that get 50 miles per gallon (or hundreds of miles per charge). Who wouldn't want to use less fuel?

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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