Bad Gas Mileage: Top 9 Major Reasons You Should Look Out

Have you been experiencing bad gas mileage of late? What causes a car to burn a lot of gas?  Well, a sudden drop in fuel efficiency of your car can be blamed on a number of factors. 

There are several reasons including poor driving habits that lead to this specific problem. The alarming thing is leaving these problems as they are can result in bigger issues and expensive repair.

There are dozens of problems that can lead to a drop in gas mileage, some of them are serious and some can be easily corrected. Here are some of the more common issues that can affect the fuel efficiency of most cars.

Top 9 Bad Gas Mileage Reasons: Get Into Details

When the fuel system does not work as designed, the efficiency level is likely to reduce. However, if the drop is sudden and serious, you should find out the reason and fix it. 

Fortunately, some problems are not serious and can be fixed by changing some of your driving habits. However, others may warrant a visit to a servicing shop and some repairs.

Bad Driving Style

Whether you believe it or not, one of the causes of poor gas mileage causes is careless driving. Some of the things that affect too much are

why is my gas going down so fast
Bad driving habits burn more fuel. (Photo:

Impulsive Driving – Engaging the brake and gas pedals frequently and without any reason causes excessive oil loss. If you can’t compromise with the thrill of rapid acceleration and revving, be prepared to spend some money on the fuel.

Over Speeding – Fuel efficiency depends on driving the vehicle within a certain speed limit. Speeding up, especially pushing the speedometer more than 120 km/h will result in bad gas mileage.

Idling Too Much – Some drivers keep the engine running when waiting somewhere. Well, it’s not good for your wallet since a running engine means money (aka fuel) is oozing down the car’s system.

Issues with Tires

Issues with tires are another common one among bad gas mileage causes. Tire problems can cause the fuel to burn at an excessive rate. 

Misaligned, uneven, and low-pressure tires make the car harder to move. As a result, the engine has to work harder and it burns more fuel.

Checking the tire’s alignment and pressure on a regular basis will prevent this problem. However, be careful not to overinflate the car for it will make the car unstable and difficult to control.

Low-Level of Oil

why is my gas mileage dropping
Low oil level decreases engine power and fuel-efficiency. (Photo: Shutterstock)

Low-level of oil is a possible culprit behind what makes a car burn gas fast. Why? Adequate fuel ensures the required lubrication and lowering the friction among various components. 

When there is not enough oil in the system, friction and heat increase and deteriorate the engine parts. The engine has to work harder and burns more fuel than needed. 

Check the owner’s manual to know the right time to change the oil in your car. It could be anything between 6,000 miles and 12,000 miles. It could be even more depending on the make and model of the vehicle.

Dirty Oxygen Sensor

Another reason for bad gas mileage is the filthy oxygen sensor. It measures the level of exhaust gasses when they leave the combustion chamber. 

The electronic control unit (ECU) uses the sensor’s data to determine the amount of fuel to send to the engine. An unclean sensor is likely to err in measurement, leading to drop in mileage.

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Fault in the Fuel Pump

It’s a no-brainer to assume that fuel efficiency also depends on the fuel delivery issues. The function of a fuel pump is to pump oil from the gas tank to the fuel injectors. 

causes of bad gas mileage
The function of a fuel pump is to pump oil from the gas tank to the fuel injectors. (Photo: Mechanic Base)

A damaged or dirty pump won’t be able to supply an adequate amount of oil to the engine, resulting in less fuel efficiency. Not replacing the pump will lead to the engine’s idling, making explosive sounds, and stalling.

Clogged Fuel Injectors and Air Filters

Clogged fuel injectors and air filters are one of the reasons for bad gas mileage. The injectors do the job of supplying oil to the engine. 

When they become dirty, the engine loses power and starts stalling now and then, leading to eating up more fuel than necessary. Similarly, air filters help with combustion by letting an adequate amount of air into the engine. 

A dirty air filter will hamper the combustion process and increase the burning of fuel. The solutions to these problems are to replace or clean these components.

Spark Plug Issues

The function of spark plugs is to ignite the air/fuel mixture in the combustion chamber, which creates the ignition needed to start a vehicle. 

Damaged or dirty plugs will lead to an engine misfire. The engine will show poor performance and there will be a big drop in the gas mileage.

what causes bad gas mileage
Defective spark plugs are another reason. (Photo: Getty Images/iStockphoto)

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Defective Mass Air Flow Sensor

It measures the amount of air supplied to the fuel injection system. The ECU collects that information and adjusts the right amount of air to be delivered to the engine. A malfunctioning sensor will lead to decreased gas mileage.

Stuck Caliper or Shoe

The disc brake caliper or drum brake shoe can get stuck for various reasons. In this case, the car will pull to one side when driving. Any problem with the brake not only declines the fuel efficiency but also makes it extremely dangerous to drive.

FAQs on Bad Gas Mileage

  1. How often should I get my car’s engine tuned for better fuel efficiency?

It’s generally recommended to get your car’s engine tuned and serviced every 30,000 to 50,000 miles or as specified in the manufacturer’s maintenance schedule.

  1. Can low tire pressure affect gas mileage?

Yes, underinflated tires can lead to increased rolling resistance, which negatively impacts fuel efficiency. Regularly check and maintain the correct tire pressure.

  1. Are there specific driving habits that can improve gas mileage?

Adopting fuel-efficient driving habits like smooth acceleration, avoiding aggressive braking, and maintaining a steady speed can help improve gas mileage.

  1. How does excessive idling affect fuel consumption?

Excessive idling wastes fuel and reduces gas mileage. Turn off your engine if you expect to be parked for more than a minute or two.

  1. Can a clogged air filter lead to poor gas mileage?

A dirty or clogged air filter can restrict airflow to the engine, affecting fuel efficiency. Regularly replace the air filter as recommended.

dirty air filter
A dirty or clogged air filter can restrict airflow to the engine. (Photo: YourMechanic)
  1. Does using the air conditioning impact gas mileage?

Using the air conditioning puts an extra load on the engine, which can decrease fuel efficiency. Use the A/C sparingly, especially at high speeds.

  1. How important is regular maintenance in improving gas mileage?

Regular maintenance, such as oil changes, spark plug replacements, and filter checks, plays a significant role in maintaining optimal fuel efficiency.

  1. Can bad fuel quality affect gas mileage?

Poor-quality fuel with impurities or a lower octane rating may negatively affect fuel efficiency and engine performance.

  1. Is driving at higher speeds less fuel-efficient?

Yes, driving at higher speeds increases air resistance and fuel consumption, leading to losing gas mileage. Driving at moderate speeds is more fuel-efficient.

  1. What impact can a malfunctioning oxygen sensor have on gas mileage?

A faulty oxygen sensor can disrupt the air-fuel mixture, leading to decreased fuel efficiency. Get it checked and replaced if necessary.

  1. Are there any benefits to using fuel additives for better gas mileage?

Some fuel additives claim to improve fuel efficiency, but their effectiveness may vary. It’s best to choose reputable products and follow the manufacturer’s guidelines.

Check the video below to see why your car gets bad gas mileage and how to fix it:

Final Words

Hopefully the information above can help you answer the questions: “Why is my car burning gas so fast?” or “Why is my car getting bad gas mileage all of a sudden?”. 

If you have any questions relevant to bad gas mileage, please feel free to leave us in our comment box then we will discuss further.