Why is My Gas Mileage so Bad?

Why is My Gas Mileage so Bad?

Is your vehicle not living up to the promises made on its window sticker? Do your real-world miles per gallon look like the prices on a fast-food value menu? If fuel economy is falling short here are some possible culprits and a few solutions to maximize your MPG.

Speed Kills … Efficiency

Slow Down

If your mileage is off, one of the easiest things you can do to remedy this situation is modify your behavior. Going full-throttle at every green light or driving 20 MPH faster than the highway speed limit can have a devastating impact on your fuel consumption. Slow down, take a breath and watch your efficiency improve.

SEE ALSO: 10 Car Noises to be Concerned About

The national speed limit used to be 55 miles an hour for a reason, even if most people hated the legislation and everyone ignored it. This restriction, on paper at least, saved fuel by allowing vehicles to operate in their most efficient speed range. If you’re not in a rush it’s something you can still do today.


Cruise Control

And if you’re zipping down the interstate, taking advantage of cruise control can also improve your vehicle’s efficiency. These computer-operated systems adjust throttle inputs more finely and accurately than a human ever can, keeping you right at the set speed. And when you’re running at a constant velocity you’re far less likely to exceed the limit, something that also improves economy.

Weight Watcher

Weight Loss

Obviously another way of upping the MPG is to reduce weight. But before you bust out a hack saw or plasma torch there’s an easier way.

Automakers fight to trim fractions of a gram from their cars and trucks, so why do you have 250 pounds of stuff in the back of your vehicle? Removing superfluous junk can improve economy, especially if you’re a pack rat, hoarder or have been living in your car. By all means keep an emergency kit with a flashlight, jumper cables and other essentials, but try to ditch the bags of sidewalk salt and dumbbells you’ve kept back there for the last two presidential-election cycles.

Pay Attention

Pay Attention

If you see that a traffic light is about to change up ahead don’t charge at it and the slam on the brakes at the last possible moment. If you back off the accelerator early your vehicle will gradually slow down, minimizing any fuel being burned. And who knows; if you’re particularly observant – or lucky – the light might even turn green right as you arrive at the intersection. Preserving momentum is a key to reducing fuel consumption.

Avoid Idling

Avoid Idling

It should go without saying, when a vehicle’s engine is running it’s also consuming fuel. Just because you’re cold or your favorite Taylor Swift song is playing on the radio is no excuse for keeping those cylinders blazing away. If you can muster the courage, switch the ignition into accessory mode. This kills the engine but still allows you to listen to music or receive a limited amount of heat in frigid weather before the cooling system reaches ambient temperature. Shutting things down when not needed can save you big money. Why is My Gas Mileage so Bad?

Regular Maintenance

Vehicle Maintenance

Modern cars and trucks are marvels of engineering. They’re capable of racking up hundreds of thousands of miles over decades of faithful service, all while delivering impressive efficiency and the creature comforts of a living room.

But maintenance is critical to keeping your vehicle running its best and minimizing fuel consumption. It may not seem like that big a deal but stay on top of oil changes, replace the air filter when necessary and throw some fuel-system cleaner in the tank every now and then. These little tricks will go a long way to boosting your mileage, though as always it’s best to follow the manufacturer’s recommendations.

Under Pressure

Tire Pressure

Tires are perhaps the most overlooked parts on a car, though they’re certainly one the most important. Remember, they’re the only components that ever touch the road, or at least they should be. Running over- or as is more likely the case, under-inflated rubbers is not just bad for fuel economy and the tires themselves but it’s also a safety issue.

SEE ALSO: What Kind of Tires Should I Buy?

Not having enough air in them increases rolling resistance, friction and causes excess heat to build up, which can have a detrimental effect on their longevity. Keep a gauge handy and try to check your vehicle’s tire pressure at least once a month.

Octane Angst

Octane Angst

It’s a myth that running premium fuel will improve your car or truck’s performance or mileage. Octane is merely a measure of gasoline’s resistance to igniting under pressure. If you vehicle calls for regular-grade fuel putting race gas in the tank isn’t going to do anything other than cost you more.

If the manufacturer recommends or requires premium, by all means fill it up with high-test stuff. These powerplants are designed to take advantage of the extra octane. Running insufficient fuel can impact performance, economy and could even cause pricey internal damage. In short, follow the manufacturer’s fuel recommendation but don’t exceed it unnecessarily.

Check out the rest of our Tips and Advice section!

  • BruceHTaylor


  • smartacus

    My personal tips include 10-20mm skinnier tires, inflating tires to 40psi, 0W30 engine oil, hardly ever use brakes, carry enough speed to chirp the tires when you are making turns at intersections, avoid all tire scrub by keeping that steering wheel dead center and only turn it using your index and thumb, draft everybody, avoid moving your foot on the gas pedal by even a millimeter, and time the lights turning green like your life depends on it, aaand make sure your wheels are balanced and all in alignment.

  • smartacus

    Hey Craig, I want to take a guess and say your picture of the cruise control is from a Hyundai…perhaps an Elantra?

  • Mike

    In our small, turbo boosted engines, higher octane has been shown to improve fuel economy. The problem is turbos generate higher compression, which leads to more engine knock. There are two ways to combat this – first, program the engine control unit (ECU) to throw away power and fuel to de-tune the engine from its optimum performance, or second, use higher octane. Octane is a measure of knock resistance with higher octane gas more resistant. The second method needs to be balanced against the increase gas cost to find the best octane for your car and driving environment.

  • The Equalizer

    “Running insufficient fuel can…and could even cause pricey internal damage.” Really? I used to own a 1997 Infiniti J30 that had “Premium Unleaded Fuel Only” plastered everywhere. I ran 87 octane in it most of the time and never suffered any engine damage. Sold it at 135K mi and the buyer now has over 200K running regular fuel. Knock sensor retards timing. I observed a slight loss in mpg but not enough to justify added cost of premium fuel.

  • Christopher Marshall

    This is why forced induction engines have a lower compression ratio than naturally aspirated units. This can be as low as 6:1 Racing non turbo engines have a compression ratio of 10:1. I agree with you on this.

  • Christopher Marshall

    A few other things you can do to increase fuel economy, is to remove the roof bars/racks/ or storage units, if you have them there. Next is when you have the oil filter, & oil in your car changed, ask them to look at the air filter also. If the filter element is even partially blocked, the engine will starve for air, resulting in high fuel consumption. I agree on the tyres needing to be checked. If your tyres are not at proper pressure, meaning less than specified by 10 psi, or more, your car will use more fuel, & the life of the tyre will be drastically shorter. The front tyres are also a good indication of wheel alignment issues. If the wheel alignment is not correct, the car will use more fuel. Starting in the mornings during winter, there is no need to “warm up” your car before driving it, as this just wastes fuel, & by the time your car has warmed up, you could have driven close to 7 kilometres, & your car will be at running temperature by then.

  • SSXT


    I agree w/this all except a partially clogged air filter, technically speaking. Modern engines won’t starve for air as they will modify the calibrated air / fuel ratio (AFR) to maintain the same Stoichiometric desired AFR. A clogged air filter WILL impact optimum power output – HP and Lb-Ft. – as less air is available to mix w/the proper fuel to maximize power. I’m not arguing that the air filter should be overlooked, just that it’s not the 1st thing to worry about. Also – and this will cause grief – stay away from the ‘oiled’ aftermarket air filters. One of the most popular brands in the US actually increases airflow @ the cost of a dangerous increase in particulates reaching the engine….Search for confirmation.


  • SSXT

    Look @ Ford and Hyundai’s turbo engines. The EcoBoosts run on Regular – 87 octane – fuel AND they have relatively high CRs. As do the Hyundais.

    …Direct Injection has mitigated many of the issues related to turbocharged engines. Reduced lag, Premium fuel requirements, higher CR for increased MPG and better off-boost drivability w/the majority of the torque available beLOW 2K RPM.

    Ford’s: Cylinders/size/CR

    -V6 3.5: 10.0:1

    – I4 2.0: 10.0:1
    – I4 1.6: 10.0:1


    – I4 1.6 9.5:1
    – I4 2.0 9.5:1
    Torque: 260 @ 1350 – 4000 rpm

    Not a fanboy, just impressed w/the new tech, as someone that has driven low CR, turbo’d Subarus for years.

  • guest

    My car gets better mileage at 65 than 55 because the rpm at 55 is just barely over idle, not the optimum efficient rpm range for any vehicle.

  • guest

    Good one LMAO

  • Jim Farnsworth

    EPA fuel mileage numbers are not promises. Calling them that perpetuates the myth that this is the fuel mileage I should expect. The numbers are for comparison between vehicles so that consumers can make and informed choice between engine options, vehicle types or brands by being informed that for example vehicle A with engine #1 will consume more fuel than that vehicle with engine #2. Or that the family sedan of brand Z is more fuel efficient that family sedan of brand Q.

    The test is meant to replicate common driving conditions but they cannot replicate all factors that effect fuel consumption. Your results will most likely vary from the test results but most likely brand Z in the example above will overall deliver better gas mileage than brand Q for you and your driving environment.

    Just my rant

  • Benito Lucena

    I’ve found that using non-ethonal gas helps n gassing up late nite or early morning helps alot too.

  • narg

    …plus helps the life of the engine.

  • narg

    The temp/warmup thing is not quite that simple. Metals expand and contract due to temps, and warming up, at least just a little bit, will help keep the engine cleaner and newer. Especially if it’s sub-freezing outside, this can cause an engine to break down faster if you bring it above idle before it gets warm. Which also can lead to lower MPGs in the future. The car companies today tell you that you can just crank and go, simply because they want to sell you a new car sooner….

  • narg

    Wrong on the oiled filters. They work much better if maintained. The oil attracts the particles so that allows larger spaces to increase airflow. There is no science behind what you get on those “searches” Not everyone out there is an expert, but a lot of folks like to gripe about nothing.

  • narg

    So… you’re one of those idiots who can’t keep speed on hills that ticks everyone off? Plus taking turns too fast risking accidents and possible injury to others? Safety and common sense is worth every gallon of wasted fuel. Don’t be stupid behind the wheel.

  • smartacus

    slutty women like you are so hungry for attention that you antagonize people on the subway till you get knocked out.

  • Christopher Marshall

    The first thing I do when I get in my car, is allow it to run long enough for me to fasten my seat belt, set my phone up for Bluetooth hands free, check the mirrors etc. By then, the cold start injector will have switched off, & the car engine will be warm enough to start. What I actually meant by “warming up” the engine is letting it run for about 1/2 hour before driving, which is pointless, but about 5 minutes before driving should be fine. I also agree with your other comments that I have read. You may agree with me on this: Some workshops, & car makers will tell you that you only need to change your oil filter every other oil change. I do not agree with this. Best policy is to change the oil filter every time the oil is changed, as there is no point putting new oil through a dirty filter!! One guy I know had a BMW 528i, & his regular mechanic was on holidays. The apprentice changed the oil in this car. 6 months later, the car came to where I was working at the time for a major service. Upon removing the oil filter cover, I found there was no filter element in it!!!

  • Christopher Marshall

    The reason is due to the “gearing” of the drive line in the car. A number of modern cars have transmissions with 6 speeds, or more, mated with a differential with a high gear ratio, somewhere in the figure of 2.5:1, or higher!! This means theoretically, but not true in reality, that the closer the engine rpm can be to idle, the less fuel it will use. Some cars configured in this manner, will change down several speeds to utilise the power of the engine for acceleration, then changing up to top afterwards.

  • Christopher Marshall

    P.S. The lower the number, the HIGHER the diff ratio, & the higher the number, the LOWER the diff ratio, NOT the other way around, like people might think.

  • guest

    I know all that having worked on my own vehicles for over 45 years. I was just stating the fact that the government doesn’t think about when setting speed limits. With a 3.42 ratio and a 6th gear of .5 I am just barely turning 1600 rpm at 70 mph, 50 mph comes at 1000 rpm.

  • Christopher Marshall

    I agree with you on this. An engine working at 1600 rpm with a speed of 70 mph means the engine isn’t working in it’s best range. Where I live in Australia, we have speed limits as low as 31 mph (close to 50 km/h). A vehicle such as this will be using a lower ratio in the transmission to be driven at that speed. I know where you’re coming from with the government lacking any thought on this. I don’t know where you’re from, and I’m thinking the USA, in which case there’s lots of open stretches of road, from pics I’ve seen, where you can drive at high speed, & not dawdle. The engine in my car is doing 3100 rpm at 70 mph. My car has a 4.5 litre V8 under her bonnet, & it’s lazy up to around 60 mph, then it starts to wake up.

  • guest

    Yes I live in Michigan just north of Detroit. There aren’t many places left here to run fast. A few places out west have higher limits and there are a couple of closed course runs for competition that are almost 90 miles long full out:o) I’m running a mild 2000 Camaro LS1 Z28 with 6 speed and 325 rwhp. Don’t know it’s top speed but it will run low 13s and coming out of 3rd gear I’m past 110 mph then I have to slow down and hope the cops didn’t see me getting on to the expressway LOL. Still gets 25+ mpg with over 142,000 miles on it.

  • Tony D

    It would be simple to replicate normal driving conditions. USE NUMBERS FROM THE ACTUAL TES DRIVING THEY DO BEFORE PUTTING INTO PRODUCTION

  • Jim Farnsworth

    Testing vehicles before production has very little to do with “normal” driving. The purpose of vehicle testing is to see how the vehicle stands up to harsh conditions and abnormal usage.

    Your “normal” driving certainly varies from mine. Same vehicle, same route, same weather, I can always get better mileage than my wife because her “normal” driving is hard on the gas, hard on the brakes, minimal following distance.

    The point of the EPA testing is that every vehicle runs the same test routine under the same conditions producing scientifically sound and repeatable data that can be used to compare vehicles.

  • mchan1

    Generally agreement except…

    1. In New England, the speed limit is generally ~60-65mph but noticed some locations ~70mph.

    2. Paying attention… on the Other drivers. Lots of crazy drivers. See many still yapping on their phones or even looking down.. how the f— can someone drive and read text at the same time? You DON’T!

    3. Octane… regular gas is fine but I noticed that my car’s engine runs smoother and quieter with premium. That was also the case with my older, 10 year old car before it was traded in for the newer one. Regular gas usage generally but treat with premium ~once/month.

    4. Idling… Good to warm up the car for ~5-10 minutes in the cold mornings during the winter. Otherwise, the engine doesn’t run well. Lots of people I know over the years do that as well esp. those that live in cold weather locations like New England.

    5. Regular maintenance… take care of your car and the car will take care of you! ‘Nuf said!

  • whatgop

    My 2015 Subaru Outback does not come close to the milage shown on the sticker. I suspect just another lie from a car manufacturer.

  • Cobranut

    Direct injection is great, UNTIL you realize the intake valves get horribly clogged with sludge every 50,000 miles, because there’s no fuel spraying over them to keep them clean.
    Most manufacturers actually require cylinder head replacement because the labor to clean and rebuild the head is more than the new head.

    Enjoy your $1,500 repair bill every year or two, and I’ll stick with my indirect injection, which still works fine even at 300,000+ miles.

  • freedomman

    Hey folks most of the information is correct. now the real scoop on why cars are not getting good mileage on the road in the USA. is because of the main cause is the EPA mandate of Ethanol in all grades of gas. It drops the by 10% or more?

  • mchan1

    Most auto makers use laboratory settings for their results which is much different than in reality (i.e. constant temperatures and steady acceleration/braking). Those laboratory variables do affect the actual mileage on vehicles.

  • whatgop

    Most auto makers use a dyno to determine MPG, but they COULD compensate for air resistance, temperature, altitude and other variables and come close to perfect, they simply refuse to. My car before Subaru was a Volvo, it averaged one MPG above the listed MPG, Subaru averages 3 to 5 below listed MPG.

  • whatgop

    The listed MPG is determined WITH ethanol.

  • Dan Mattingly

    Strange that the Toyota FJ cruiser is meant to run middle or premium grade fuel. It can run regular but, YOUR MILEAGE GOES DOWN. Toyota even states this, From as much as 22 MPG( non-ethanol premium) to as low as(Regular ethanol) 19 MPG. We drive the speed limits and don’t drag race at every light and have found this to be true. Explain that one you rocket scientist, Speed does affect mileage per gallon due to the duration of time to burn efficiently. Faster you go the less time to burn the fuel completely.

  • Quizicat

    Yes the EPA mileage is listed with Ethanol. But gas without Ethanol will get you better gas mileage. So you can potentially beat the EPA rated mileage.