The Main Causes Of Bad Gas Mileage

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Figuring out what is ruining your monthly gas bill and what you can do about it.

Read in this article:

What Gas Mileage or MPG Means

Bad gas mileage is seen as a negative for obvious reasons, and those that have higher mpg figures are preferred: but what is MPG? MPG means "miles per gallon" and is the standard way to measure gas mileage for cars and trucks in the USA, stating how many miles a vehicle can drive on a gallon of gas.

The EPA publishes three MPG figures to indicate the average gas mileage of a car - its fuel consumption in the city, on the highway, and a combination of the two. EPA testing is complicated, and you can read more about the EPA test procedures here. For now, let's look at what gas mileage figures is considered bad for your type of car and which problems cause very poor gas mileage.

MPG Meaning CarBuzz

How Much Mileage is Bad Mileage?

The EPA's city/highway/combined MPG figures vary according to vehicle type. A gas-powered SUV will be far heavier on fuel than a compact car, hybrid, or diesel. What is considered poor fuel economy for a compact car might be excellent for an SUV. Large, heavy gas-powered trucks and SUVs are generally considered cars with 'bad' MPG figures due to their large, heavy structures and large displacement engines that offer high outputs. The same is true for muscle cars or supercars that prioritize performance over frugality.

Here is an example of how much city/highway/combined mileage figures can vary:

Make and ModelBody styleEngineDrivetraiMPG
Cadillac EscaladeSUV6.2L V8 gas4WD13/19/16
Ford F-150Truck2.7L Turbo V6 gas2WD20/26/22
Acura MDXSUV3.5L V6 gasFWD19/26/22
Nissan VersaSedan1.6L inline-4 gasFWD32/40/35
Mitsubishi MirageHatch1.2L inline-3 gasFWD36/43/39
Hyundai Elantra HybridSedan1.6L inline-4 hybridFWD53/56/54
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Gas Mileage for Cars CarBuzz

The Main Reasons for Bad Gas Mileage or Poor Fuel Economy

Here are the main causes of bad gas mileage/mpg figures:

  • The vehicle: As you can see from the list above, the type of car can be one of the main reasons for bad gas mileage ratings. Even the best trucks won't get 30 MPG combined. A big SUV or executive car will never be as economical as a small car - the best compact cars reach nearly 40 MPG combined and hybrids exceed 50 MPG.
  • Incorrect tire pressure: Low tire pressure causes increased rolling resistance and is one of the main causes of poor gas mileage. Frequently check your tire pressures.
  • Bad filters: A blocked or dirty air intake or air/fuel filter affects the air/fuel mixture that enters your engine, leading to poor economy.
  • Bad sensors: Malfunctioning oxygen sensors or other engine sensors can affect fuel consumption.
  • Fueling system: Bad fuel injectors or other fueling-system components can wreck your car's fuel economy.
  • Ignition system: Bad spark plugs, coils, or other ignition-system components can cause poor running and bad mileage figures.
  • Oil: The incorrect grade of oil can affect economy and even harm your engine.
  • Idling: Excessive idling uses a lot of fuel.
  • The air-conditioner: The A/C draws power from the engine, increasing fuel use. Switch it off when it's not needed and rather drive with your windows open in town. Read more here about the effect the air conditioner has on fuel economy compared to open windows.
  • Your driving habits: The way you drive has a big impact on fuel economy. Aggressive driving, harsh acceleration, and high-speed driving waste fuel. Read more on driving habits that can damage your car without you even knowing it.
Bad Gas Mileage Pexels.com

Conclusion

You can't do much to get good fuel economy out of a gas guzzler like the Cadillac Escalade and it's ilk, but you can optimize its fuel efficiency. Pay close attention to the list above - it can save you some gas money. A properly maintained car and sedate driving will reward you with better overall economy. Diesel and electric or hybrid vehicles like the Hyundai Elantra Hybrid are more economical than gas vehicles and might be an option, too, especially if you drive long distances.

Average Gas Mileage of a Car unsplash.com

FAQs

Why is my car getting bad gas mileage all of a sudden?

If your car suddenly starts using more fuel, there is probably a mechanical problem with the ignition or fueling system that should be checked out by a competent mechanic. Don't ignore the problem, as it could harm your engine. Keep in mind that sudden changes in usage patterns and the weather also affect fuel economy.

How can I determine a car’s fuel economy before I buy it?

Your new car's Monroney window sticker shows the EPA-estimated MPG figures. You can also compare fuel economy on the EPA's fueleconomy.gov website. For each car, your expected annual fuel costs will be shown, as well as how much more or less the car will cost to fuel compared to the average new vehicle.

Does idling my car to warm it up in the morning have a big effect on fuel economy?

An engine uses the most fuel and is at its most inefficient when it's cold. A properly maintained modern car with the correct coolant grade and oil for your state's weather should not need more than 30 seconds of idling before you can drive off, even on a cold morning. Don't work the engine hard while it's cold, but don't idle it for a long time either.

Why is my car heavier on fuel in cold weather?

A cold engine and transmission are inefficient and take longer to warm up in cold weather. This is exacerbated by frequent short trips, preventing them from ever warming up properly. Additionally, cold-climate equipment like interior and seat heaters and defrosters draw power that increases fuel use. In snowy conditions, winter tires with a higher rolling resistance, reduced tire grip, snow buildup, and the use of 4x4 reduce economy too.

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