The engine air filter is designed for your vehicle. If dirt seeps through the wrong filter, it can chop and scratch the cylinders, which reduces power and can lead to block overheating, cracking, or even seizure. Decreased fuel economy is a clear sign of a faulty or dirty air filter. A bad or dirty air filter restricts air flow and reduces oxygen in the mixture.
Your engine compensates for this by consuming more fuel to produce enough power to move the same distance or speed as it could with a clean filter. Expensive large diesel engines have air filter restriction indicators that show when to repair the air filter. If you notice unusual noises, in particular a coughing, clicking or spitting noise, this suggests that the engine is not receiving enough airflow, which means that the air filter needs to be replaced. Over time, the engine air filter can become dirty and lose its ability to filter air entering the engine.
The air filter resembles a bunch of stiff cloth folded into an accordion, and acts just like the one in your house, trapping incoming dirt so it doesn't get into the rest of the system. When the air filter becomes too dirty, it will clog and the engine will not be able to draw enough air into the combustion chamber. Driving with a dirty air filter may seem like no big deal, but doing so can have a negative impact on your health and that of your vehicle. For this reason, most car manufacturers recommend changing the air filter every 12,000 miles (approximately 19,000 km) or every 12 months, whichever comes first, regardless of how dirty the air filter appears to be.
The dirty air filter restricts air supply to the engine, causing unburned fuel to form a soot residue that accumulates in the spark plug. All captured dust, grease and other contaminants eventually clog the filter so much that it blocks the flow of clean air to the engine. A new air filter is white or off-white, while a dirty air filter will appear darker with visible dirt and debris. In some cases, a severely restricted filter can also allow contaminants to enter the turbocharger and engine.
A dirty air filter is one of the things that can cause the Check Engine light to come on, due to an inadequate supply of air to the engine that causes carbon deposits to build up. Vehicles have an air intake system to suck in air and purify it, before using it in this air-fuel mixture. Before reaching the engine, the filtered air passes through a mass flow meter, which measures how clean the air is and determines the correct air-fuel ratio for the mixture to maximize fuel efficiency and performance. Improper filter installation or incorrect filter installation can leave the engine exposed to dirt and debris.
A dirty air filter reduces the amount of clean air that reaches the engine, which decreases its power and performance.