For most shoppers interested in buying a car, whether new or used, fuel economy is a concern. How much will it cost to fill up? How long will it travel between gas stops? Those are common questions asked by car shoppers who want to minimize their monthly fuel bills, but drivers interested in a used car also have to ask a different question: Will a used vehicle still get the same gas mileage as it did when it was new? After all, it's possible that years of use may take a toll on the engine, limiting gas mileage. How do used cars perform when it comes to fuel efficiency? We'll investigate.

Don't Expect EPA-Rated Mileage

Before we cover fuel efficiency in used cars, it's important to mention that shoppers shouldn't expect their vehicle to get Environmental Protection Agency (EPA)-rated mileage regardless of whether it's new or used. EPA ratings are, in many cases, a best-case scenario, especially before the 2008 model year. Prior to 2008, EPA's tests had little real-world relevance because they were based on slower-than-usual speeds and didn't consider the use of accessories such as air conditioning. Since 2008, tests have more real-world pertinence, but for many drivers, the figures are still a reach.

Our point is that your car probably won't get the new mileage if you're comparing its actual fuel economy to EPA tests, but that hardly means that the car is flawed. It's unlikely that the car ever met those numbers even when it was brand new.

Aging Issues?

In general, we believe that the idea of fuel economy getting worse with age is a myth. It's commonly discussed, but we don't think that most cars will return noticeably worse gas mileage as they get older.

With that said, it's not a hard-and-fast rule. Engine performance largely depends on maintenance, and if a car owner fails to keep up with maintenance, we could easily see fuel economy start to slip. In fact, if a car owner fails to keep up with maintenance, we imagine that other issues will also develop, including larger engine problems and a loss of horsepower or torque.

Getting the Best Mileage

As a result, we think the key to getting new-car gas mileage from a used car is simple: maintenance. Buy a used car that's been well maintained by previous owners, and you're likely to get about the same mileage as you would've if the car had just rolled off the showroom floor. Buy a used car that's been poorly maintained, and you're likely to see fuel economy issues -- among other problems with the car.

This is one argument in favor of certified pre-owned cars, which are often among the best used cars available. Since certified pre-owned vehicles -- which usually come with a warranty from the automaker -- are well maintained and reasonably recent, they're likely to return approximately the same fuel economy that they did when they were first sold.

If you're not sure whether the used car you're considering has been well maintained, we suggest getting a mechanical inspection from an impartial mechanic or dealership. While such an inspection can be costly, it may also save you big money if it helps you avoid a problematic car.

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Doug DeMuro has a wide range of automotive industry experience, from work at a Ferrari dealership to a manager for Porsche North America. A lifelong car enthusiast, Doug's eclectic vehicle purchases include a Porsche 911 Turbo, an E63 AMG wagon, an old Range Rover and a Mercedes Benz G-wagen.

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