Unlike an air filter in the home that helps clean the air you breathe, an air filter in your car is actually designed to help your car work more efficiently. Your car's air filter removes debris, pollen and dirt so that the air that enters your car's engine won't create damage from particulates. Clean air is vital for the long-term maintenance and fuel efficiency of your car; for every gallon of fuel your engine burns, it needs about 10,000 gallons of clean air to pass through. A dirty air filter makes your car work harder, which wastes gas and hurts your car. Replace your car's air filter every 12,000 to 15,000 miles, and if you live in a climate that is very dusty, replace it even sooner.