Your engine combines air and gasoline in its internal combustion chamber and creates power for your car to run. This air reaches it through an air filter that works to keep out the road debris, bugs, and other contaminants that can cause damage to 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 get clogged and the lack of air can affect the overall performance of your car.
Auto companies recommend that you change the air filter every 10,000 to 15,000 miles or 12 months. However, if you typically drive in dusty or rural areas, you might want to have your mechanic check and change it more frequently or every 6,000 miles. Driving in crowded areas where there is heavy traffic and you need to stop and start more often also requires you to replace the air filter sooner.
You can make note of these symptoms that indicate your air filter needs replacing.
Lower fuel economy
Your engine compensates for the lower amounts of oxygen by consuming more fuel to produce enough power. Thus, if you notice that your average mileage per gallon is going down, that 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. Thus, the cleanliness of the air filter on newer cars shouldn't significantly affect fuel economy.
Misfiring or missing engine
An insufficient 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 that in turn cannot deliver the necessary charge to the engine. You’ll notice that the engine does not start up easily, and is misfiring or jerking.
Unusual engine sounds
When the car is stationary with the engine turned on, you should sense the smooth hum of an efficient engine. If you notice your car vibrating or hear a coughing or slipping sound, this could be an indication of rough idling. This condition occurs because of a damaged spark plug resulting from a clogged air filter.
Service Engine Soon light comes on
The car engine combines 10,000 gallons of air with one gallon of gasoline to power your car. Inadequate air can result in deposits accumulating on the engine and you will notice that the Service Engine Soon light has come on. If that happens, have your mechanic check the air filter also.
Air filter appears dirty
A clean air filter appears white or off white in color, but as it accumulates dust and dirt, it will seem darker in color. However, very often, the inner layers of filter paper inside the air filter might have dust and pollen 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. Also, follow the manufacturer’s instructions regarding replacement.
If your car does not respond adequately when you press the accelerator or if you notice jerking movements, this is an indication that your engine is not receiving 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 and exiting 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 fuel in the exhaust ignites because of the heat.
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.