What Is a Air Filter?
The air filter is a paper, foam or cotton element housed in a plastic casing — called the airbox — mounted on top of or beside the engine. It filters the air drawn into the engine for combustion, preventing abrasive particles from entering the cylinders, pistons and valves. Without an air filter, even fine road dust would act like sandpaper inside your engine, causing rapid and irreparable wear to precision components.
What Does the Air Filter Do?
Every modern petrol and diesel engine requires a precise mixture of air and fuel to combust efficiently. The air filter ensures that the air entering this mixture is clean. A contaminated air supply reduces combustion efficiency, increases fuel consumption and can cause long-term damage to the engine. On turbocharged engines, dirty air can also damage the delicate blades of the turbocharger compressor wheel.
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Get My Free Fault Scan →Symptoms of a Failing Air Filter
A blocked or dirty air filter restricts airflow into the engine. Common symptoms include reduced acceleration, increased fuel consumption, black smoke from the exhaust on petrol engines, a rough idle, and in some cases an engine management light caused by the MAF sensor detecting incorrect airflow. The engine may feel sluggish, particularly under load.
When Should the Air Filter Be Replaced?
Most manufacturers recommend replacing the air filter every 12,000 to 15,000 miles or annually — whichever comes first. Drivers in dusty environments or who frequently drive on unpaved roads should replace it more often. Air filter replacement is one of the cheapest and quickest services you can do — typically costing between £10 and £30 for the filter itself.
If you are experiencing symptoms related to your air filter and are unsure whether it needs replacing, a free MotorLoom fault scan can help identify whether the component is likely at fault - giving you the most likely cause and estimated repair cost before you visit a garage.
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Related Parts
Other components that work alongside or are related to the air filter: