Anyone familiar with cars knows changing an engine air filter is an important part of routine maintenance, but why do engines need an air filter to begin with? Just why are they so important and how do they affect performance?

No Filter

The first engines were built without air filters, and it wasn’t great for them. Both gas and diesel engines require large volumes of air for combustion to take place, so it’s important to force the right amount of air into the chambers, but not indiscriminately. There are a lot of tight clearances once inside, and if the system is picking up even small particles, their introduction to the system can have long-time cumulative or immediate catastrophic effects. Air filters were introduced early on as a way to get the engine the air it needs while keeping harmful debris out.

Filter Needed

The first air filters were water and oil “bath” types. These worked by inducting air through a deep U-shaped passageway with a pool of water or oil (oil proving the more effective design) at the bottom. The force of the air flow coupled with the shape of the route worked to trap particles in the baths, but as you can imagine, it wasn’t very pretty to service. It also had performance limitations. Next was the introduction of paper filters which were placed directly on top of the carburetor. Their filtering substrate was pleated to increase the surface area through which air can travel. As better fuel injection technologies emerged, the air filter was moved further from the engine and underwent many design iterations in terms of shape and material. Ultimately, the “perfect” air filter design is still a matter of discussion.

Clean Air Action

All filters are expected to get dirty, it’s kind of their job. Filters made of paper, cotton and other fibers (the most common types) will need to be replaced every 10,000 to 50,000 miles, depending on driving conditions. With such variance, it’s important to check for dirty filters during routine maintenance, as regularly driving down dusty roads will shorten their life considerably. And driving with a clogged filter can drastically lower performance, fuel economy and even cause an engine to die completely. Luckily, dirty filters are pretty easy to spot once removed from their housing and even easier to change. The latest technologies include washable filters designed to last the life of the vehicle, but these are not generally standard and require specific cleaning chemicals and treatments.

Always take care to prevent anything from entering the engine while a filter is out, or contaminating the inside of the filter itself. Your engine will thank you for the breath of fresh air.

Check out all the air filters available on NAPA Online or trust one of their 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on whether an engine air filter is necessary, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo credit: Blair Lampe

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