7 Reasons Why Your Car’s Gas Mileage is Getting Worse

As your car ages, you may notice a decline in its gas mileage. While it’s true that poorly maintained vehicles are more likely to experience worsening fuel efficiency, there are specific factors that can contribute to this issue. In this article, we will explore seven common reasons why your car’s gas mileage may be getting worse and discuss the importance of routine maintenance to ensure optimal fuel efficiency.

Clogged or Damaged Fuel Injectors

Fuel injectors play a crucial role in delivering fuel into the engine cylinders. When these injectors become dirty or clogged, they spray fuel inefficiently, leading to reduced engine efficiency and lower fuel economy. Think of it as a poorly pressurized shower head that hampers water flow. Cleaning the fuel injector nozzles can often resolve the issue, but in some cases, replacement may be necessary if internal damage is causing a bad spray pattern.

Old Engine Air Filter

The engine relies on a steady flow of air to generate power for your vehicle. However, if the engine air filter is dirty or clogged, it restricts the airflow, causing the engine to burn more fuel to maintain the desired speed. Older cars that rely on carburetors are particularly susceptible to this problem. It is recommended to replace the engine air filter every 15,000 to 30,000 miles or as per your owner’s manual guidelines.

Dirty Oxygen Sensor

Modern cars, since around 1996, utilize oxygen sensors instead of carburetors to maintain the ideal air-to-fuel ratio for combustion. An oxygen sensor measures the exhaust gases’ richness or leanness and sends signals to the car’s computer to adjust fuel injection accordingly. A dirty oxygen sensor can lead to incorrect measurements, causing the engine to burn excessive fuel and decreasing fuel efficiency by up to 40%. If your check engine light is on, a faulty oxygen sensor could be one of the culprits.

Clogged Fuel Filter

Fuel filters prevent contaminants from reaching the engine and causing damage to important components like fuel injectors. A clogged fuel filter restricts fuel flow, lowers fuel pressure, and adversely affects engine performance. It is essential to change the fuel filter every two years or every 30,000 miles, especially for older vehicles.

Bad Ignition System Parts

The ignition system, consisting of coils, spark plugs, and wires, is responsible for igniting the air-fuel mixture in the engine cylinders. If any of these components malfunction, it can lead to misfires, where the fuel in a cylinder fails to combust. Unburned fuel not only wastes gas but also decreases fuel economy. Symptoms of a faulty ignition system may include rough idling, stumbling, or a general decrease in engine power.

Old or Incorrect Engine Oil

There is a common misconception that older cars should use thicker engine oil to prevent leaks. However, thicker oil creates more resistance between engine parts, resulting in lower fuel efficiency. It is crucial to use the right motor oil as specified in your owner’s manual. Regular oil changes with the recommended oil type help keep your engine lubricated and protected, ultimately preserving fuel efficiency.

Dirty Mass Airflow Sensor

Mass airflow sensors measure the amount of air entering the engine and communicate this data to the car’s computer to determine the correct air-to-fuel ratio. A dirty airflow sensor causes the computer to miscalculate the mixture, leading to decreased fuel efficiency or even engine stall. It is important to clean the mass airflow sensor with a specialized cleaning spray to ensure accurate readings and optimal fuel economy.


Maintaining good gas mileage is essential for both your wallet and the environment. By addressing the seven common issues mentioned above, such as clogged fuel injectors, dirty air filters, faulty oxygen sensors, and more, you can improve your car’s fuel efficiency. Regular maintenance and timely replacement of parts are key to keeping your vehicle running smoothly and ensuring optimal gas mileage. Take care of your car, and it will reward you with improved fuel economy and a longer lifespan.