Your Older Vehicle Isn’t Getting The Mileage You Think It Should – What To Check First

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Do you think your older vehicle should be getting better gas mileage? Here’s a checklist to help before you head to the mechanic.

Are you worried that your older vehicle isn’t getting the mileage it was designed to? Before you head to the dealer or your trusted local mechanic for help, there are some things you should do. We will assume that your vehicle is maintained according to the owner’s manual. Also, before we go any further, we suggest you have checked that your tire pressure is properly set (here’s how to do that) and that there are no obvious signs of major problems like a cloud of blue smoke following you around town, or a sound like a can of shaken marbles when your car accelerates.

If your vehicle’s mileage is making you question if something is wrong, the first thing to do is to verify what, exactly,  you are presently getting. Do that by filling up your vehicle at a pump on a flat surface, not an incline, and stop filling when the nozzle clicks. Don’t overfill. Now, reset your trip odometer. Drive the vehicle on your normal routine until it is below half a tank and then refill the same way. Record your driven miles from the trip odometer and the fuel you put in and divide miles by gallons. Then repeat this a couple of times. The MPG you record should be similar if you drove for more than half a tank on your normal schedule each time. This tells you what your mileage is.

 – Looking for a vehicle that won’t drain your wallet at the pump? Start your search at, go to and use the tool to select your specific vehicle with its specific drivetrain (AWD or not, which engine, which transmission etc). The tool walks you through that and it will then tell you what the EPA estimates your exact vehicle should be getting for mileage based on the group’s most current data. One thing to take note of is that the mileage that was on your window sticker ten years ago may not have been the best estimate. The EPA has revised its methods for estimating fuel economy multiple times in the past couple of decades and it is now more conservative, meaning its estimates have gone down a bit for most vehicles. If you want to compare the EPA’s original estimate to what they guess your vehicle’s MPG will be now, they have a tool for that too. 

The EPA will give you three numbers, City MPG, Highway MPG, and Combined. Don’t overthink these. Don’t try to take a 20 mile Highway trip and then try to calculate your mileage. That is not how these numbers work. These are estimates and averages and they assume you drove for a couple of hundred miles before you calculated your particular mileage to compare. If you are in the city and drive almost exclusively in the city and suburbs, then the low-end City mileage is the best number for you to compare to. If you primarily drive on a highway without heavy traffic, then the Highway estimate may be a good predictor for you. For most of us, the Combined estimate works best and it is always in the middle of the other two estimates EPA publishes.


Next up, be aware that if you are trying to calculate your mileage and it is above 90F or below 40F when you do it, the EPA estimates are going to be a bit higher than you will see in actual driving. The EPA estimates are for long-duration multi-season mileage. Not the mileage you will get with winter blend fuel in a cold snap or when your AC is working overtime during a heat wave.

Now that you have a good comparison, how is your vehicle doing? Is it within 10% of the EPA estimated fuel efficiency for your exact model? If it is, you should stop now and put your mind at ease. The EPA offers estimates, not minimums. If your vehicle is rated at 18 MPG Combined and your records show you are getting 16.9, it doesn’t mean you have a problem with your engine. It means your driving route, driving style, and your particular vehicle fall on the lower side of the estimates.

If you are below by more than 10%, there are two things to verify that are the most common reasons why your mileage might be a bit low. First up is tires. Are you using the correct size and style for the vehicle? If you bought a truck or SUV used and the prior owner up-sized the wheels and added different tires from those the vehicle was delivered with that could be the reason for your lower than expected mileage. Also look to be sure that any prior owners didn’t modify the engine in any way. No special air intakes, no “upgrades” of any kind. Last, are you using the specified fuel grade? If your car maker suggests 91 octane and you are sneaking in cheaper 89 or 87, you are wasting your time trying to find other problems that would cause lower than expected fuel economy.


John Goreham

John Goreham

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