Air filters in a car removes dust and debris from the incoming air to prevent them from entering the engine cylinder to decrease wear & tear and contamination of oil. Air filter are usually made of paper, foam and cotton. If the air filter in a car is not clean, the fuel efficiency is decreased, performance of the car will deteriorate over time and it can also affect the air flow sensor. White smoke, decrease in mileage, and loss of horse power of the car are the symptoms for a dirty air filter. Air filters need to be replaced depending on the type of place the car is being driven. If the place is dusty, then the car air filter might need to be changed often. Usually, The air filter is replaced with the replacement in oil change. Air filters are inexpensive and helps in maintaining a good condition of the car so one should replace them yearly or for every 50,000km. Air filters come in all different shapes and sizes for old cars which use carburetors and the modern cars with fuel injection technology.