9 Reasons Your Car Is Guzzling Gas

Nicole Arata
March 29, 2018

reasons for bad gas mileage

Your car can only go so far on a single tank of fuel — but there are ways to squeeze out the best results. 

Making sure your car is getting efficient fuel economy can save you money at the gas station and sizably cut down on your car’s air pollution. To get the best gas mileage, you’ll want to ensure your car is in top shape and your using smart driving habits. 

Here are nine issues that can keep you from getting the most miles per gallon.

1. Spark plug problems

The National Institute for Automotive Service Excellence says misfiring due to bad spark plugs can decrease fuel economy by 30%. If your car isn’t getting the proper combustion-generating spark at the right time, your engine power is wasted, and your gas mileage plummets. Spark plugs typically last 100,000 miles, and often start misfiring when they’re down to their last 20,000. 

2. Clogged engine air filter

Your engine sucks in air to power itself. If that airflow is restricted by a dirty air filter, it’ll use more fuel to compensate. This is more true of older vehicles, as newer cars have computer systems that detect poorer air quality and adjust the air-fuel combination in your engine accordingly. Still, newer vehicles pay for this with decreased acceleration power. 

Check your owner’s manual for the expected air filter lifespan (usually between 15,000 and 30,000 miles), and have your mechanic swap it during the closest oil change.

3.  You’re skipping oil changes

Changing your oil at the recommended intervals is arguably the single best thing you can do to keep your car running smoothly. If you go too long without fresh oil, it’ll cause all sorts of problems, including worse gas mileage. When oil ages and thickens, it works harder to get to and through the engine. The engine is then more likely to heat up and run slower, requiring more fuel to get where it needs to go.  

The distance you can go between oil changes varies by the type of car you have, but often it’s at least 5,000 miles.

4. Clogged fuel injectors

Fuel injectors are responsible for putting gas into your engine, so if they’re not working well, you’re car’s not going to work efficiently. Fuel injectors can clog when carbon deposits build up over thousands of miles of driving. 

Talk to a trusted mechanic if you notice rocky idling, problems accelerating, stalling and increasing emission levels — it could be a sign the injectors are the problem. And you don’t need to bother with fuel injector cleaners you see at the store. They’re not guaranteed to correct the problem.

Get it diagnosed by a professional

5. Not enough air in the tires

Properly inflated tires take less energy — and thus fuel — to push. The U.S. Department of Energy says you can improve your fuel economy by 0.6% on average — and sometimes up to 3% — by keeping your tires inflated to the ideal pressure. 

Having your tires at the right pressure can help avoid other issues, too, such as blowouts or bad alignment (the latter of which can also affect your gas mileage). You can find the recommended pressure on the side of your tire, and you can check your tire pressure and inflate them yourself.

» MORE: What should I do when tire pressure warning light comes on?

6. Idling too much

Leaving your engine idling means needlessly burning fuel. Different types of cars and other factors make it difficult to pinpoint the exact amount of gas you burn, but AAA has stated a good rule of thumb is that you use a quarter-gallon of gas for every 15 minutes you idle. 

So, if you’re waiting in the car while a friend grabs something from the store, consider turning off the car. And if it’s cold, you likely only need to warm up your car for 30 seconds or so — not minutes at a time.

7. Driving too fast

Aggressive driving, including speeding and accelerating suddenly, gobbles up gas. While each vehicle reaches its optimal gas mileage at a different speed, efficiency usually decreases rapidly above 50 mph, according to, the U.S. government source for information on energy efficiency. It also estimates that each 5 mph you drive over 50 mph is like paying an additional 18 cents per gallon for gas.

Sticking to the speed limit will help increase your miles per gallon, as will smooth, even braking and easing into the gas after a stop.

8. Blasting the air conditioning 

Most vehicles use power from the engine to run the air conditioning. How much fuel gets used depends on the car’s size, the outdoor temperature and other operating conditions. But government sources have estimated that using air conditioning can reduce an average vehicle’s fuel economy by a hefty 20% to 25%. 

To keep your car cool during hot weather, try parking in the shade whenever possible, using window screens and keeping the windows cracked open. You can help your fuel mileage by driving with the windows down at lower speeds and saving the A/C for the highway.

9. It’s winter

Sometimes, it's just seasonal. Cold weather increases engine and transmission friction, and causes your engine to take longer to warm up to its most fuel-efficient temperature. Heated seats, letting your car warm up long enough to defrost the windshield, even denser air outside dragging on your vehicle can all also play a role.


Nicole Arata

About the Author

Nicole has written about car ownership for multiple media outlets, and her work has been featured in USA Today, Yahoo Finance and the Los Angeles Times.