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 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.
When To Replace the Engine Air Filter:
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. — causing you to stop and start more often also requires you to replace the air filter more frequently. Most vehicles also have a cabin air filter used to clean air entering the car’s interior, but it has a different maintenance schedule than an engine air filter.
Should you fail to replace your air filter at the suggested intervals, you may notice distinct signs of it needing replacement.
8 Signs Your Air Filter Needs Replacing
1. Reduced Fuel Economy. Your engine compensates for lower amounts of oxygen by consuming more fuel to produce sufficient power. Thus, if you notice your gas mileage lowering, it could indicate that the air filter needs replacing. However, this is true only for carbureted cars, most of which were made before 1980. Carburetors mix air and fuel at the ideal ratio for the internal combustion engine. Newer cars with fuel-injected engines use onboard computers to 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.
2. 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 the engine does not start up easily, misfires, or jerks roughly as a result.
3. 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 coughing or popping noises, it is often from a clogged air filter causing dirtying or damaging a spark plug.
4. 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. The inadequate air supply can result in carbon deposits — the byproduct of combustion — accumulating in the engine and setting off the Check Engine Light. If that happens, have your mechanic check the air filter among other diagnostics. The Check Engine light can illuminate for a variety of reasons. A mechanic will need to scan the onboard computer for the stored trouble code that triggered the Check Engine Light as well as the source of the problem.
5. 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. This makes it essential that you have your mechanic check the air filter when you take the car in for maintenance. Make sure to follow the manufacturer’s instructions regarding replacement.
6. 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. Since it improves airflow, replacing your air filter can improve acceleration or horsepower by up to 11%.
7. Black, Sooty Smoke or Flames Exiting the Exhaust. The 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 caused by heat in the exhaust system igniting the unburnt fuel near the tailpipe. This is a potentially hazardous condition and needs to be diagnosed right away.
8. 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. Instead of seeing smoke or flames coming out of the exhaust pipe, you’ll smell gasoline. This is a clear indication that it’s time to replace the air filter.
Replacing your air filter benefits car longevity and engine performance. Engine air filters prevent harmful debris from damaging crucial components to keep the car running smoothly. They contribute to efficient driving by helping maintain the right air-to-fuel ratio, preventing the excess consumption of gasoline. Dirty air filters keep the system from getting the right amount of air or fuel and make it harder for the engine to perform its role. Having a fully-functioning engine air filter is critical to optimal car operation.