Common Signs of a Dirty Air Filter

A car air filter cleans the air entering the engine. Signs of a dirty air filter include a misfiring engine, unusual noises, and reduced fuel economy.

A car engine combines air and gasoline in the combustion chamber to create power. This air reaches the engine through an air filter that works to keep out road debris, dirt, bugs, and other contaminants that can damage the engine. At the same time, the air filter must allow enough air to reach the engine so that it can perform effectively. Over time, the air filter can become dirty and clogged, and the lack of air can affect the overall performance of your car.

Most auto companies recommend that you change the air filter every 10,000 to 15,000 miles, or every 12 months. However, if you typically drive in dusty or rural areas like Scottsdale, Arizona, or San Antonio, Texas, you might want to have your mechanic check and change it more frequently, such as every 6,000 miles. Driving in crowded areas where there is heavy traffic – including Los Angeles and Washington D.C. – and you need to stop and start more often also requires you to replace the air filter more frequently.

Make note of these symptoms that indicate your air filter needs replacing:

Reduced fuel economy

Your engine compensates for lower amounts of oxygen by consuming more fuel to produce sufficient power. Thus, if you notice that your fuel economy is going down, it could be an indication that the air filter needs replacing. However, this is true only for carbureted cars, most of which were made before 1980. Newer cars with fuel-injected engines have onboard computers which calculate the amount of air taken into the engine, and adjusts the fuel flow accordingly. Therefore, the cleanliness of the air filter on newer cars shouldn't significantly affect fuel economy.

Misfiring engine

Restricted air supply from a dirty air filter results in unburnt fuel exiting the engine in the form of soot residue. This soot accumulates on the spark plug, which in turn cannot deliver the necessary spark to combust the air-fuel mixture. You’ll notice that the engine does not start up easily, misfires, or jerks roughly.

Unusual engine sounds

In normal circumstances, when your car is stationary with the engine turned on, you should sense the smooth rotation of the engine in the form of subtle vibrations. If you notice your car vibrating excessively or hear a coughing or popping sound, it is often due to a dirty or damaged spark plug resulting from a clogged air filter.

Check Engine Light comes on

Many modern engines suck up about 10,000 gallons of air for every single gallon of fuel burned in the combustion cycle. Inadequate air supply can result in carbon deposits accumulating in the engine which may set off the Check Engine Light. If that happens, have your mechanic check the air filter among other diagnostics.

Air filter appears dirty

A clean air filter appears white or off white in color, but as it accumulates dust and dirt, it will look darker in color. However, very often, the inner layers of filter paper inside the air filter might have dust and debris that is not visible even in bright light. Therefore, it is essential that you have your mechanic check the air filter when you take the car for maintenance. Make sure to follow the manufacturer’s instructions regarding replacement.

Reduced horsepower

If your car does not respond adequately or if you notice jerking movements when you press the accelerator, this could indicate that your engine is not receiving all the air it needs to perform. Replacing your air filter can improve acceleration or horsepower by up to 11%.

Black sooty smoke or flames exiting the exhaust

An inadequate air supply can result in some of the fuel not burning completely in the combustion cycle. This unburnt fuel then exits the car through the exhaust pipe. If you see black smoke coming from your exhaust pipe, have your mechanic replace or clean the air filter. You might also hear popping sounds or see a flame at the end of the exhaust. This happens when the heat in the exhaust system ignites unburnt fuel near the tailpipe. This is a potentially hazardous condition and needs to be diagnosed right away.

Smell of gasoline when starting the car

If there isn’t enough oxygen entering the carburetor or fuel ejection system when you start the car, the excess unburnt fuel exits the car through the exhaust pipe. That’s when you’ll smell the gasoline and know that it’s time to replace the air filter.