The air cleaner looks dirty when it starts to darken and dirt becomes noticeable. Usually, a new engine air filter is white or off-white in color. If the filter is only slightly dirty, it can be cleaned by tapping it to release loose debris. However, if the air filter is covered with dirt and other contaminants, it needs to be replaced.
Not enough air will enter the engine if the air filter is dirty, causing poor acceleration and a noisy idle. Most automotive companies recommend changing the air filter every 10,000 to 15,000 miles or every 12 months. If you drive in dusty or rural areas, it's a good idea to have your mechanic check and change it more often. The white sheet test is a smart way to determine if the air filter is dirty.
Hang a clean white sheet approximately 5 inches from one of the vents for at least an hour. If the sheet turns gray, you have a dirty air filter. The most obvious sign that you need a new air filter is if the one you have is gray and dirty. Be sure to take out the air filter and check it out at least once every two months.
Running your car without an air filter allows dirt, leaves, debris, insects and a multitude of air pollutants to enter. A dirty air filter reduces the amount of clean air that reaches the engine, which decreases its power and performance. You may even experience a slight hiss if airflow is limited due to excessive buildup on the filter screen. Pleated filters made of disposable nonwoven fabric have smaller pores and can contain more particles than a flat surface.
Replacing the air filter is actually one of the easiest DIY tasks you can perform on your vehicle. At the same time, the air cleaner must allow enough air to reach the engine so that it can operate effectively. Now that you know the problems that a dirty or clogged air filter can create, you'll want to change yours right away. Like other car maintenance services, air filter replacement costs vary depending on the model of the car and where you are looking.