The Best Engine Air Filters

Gas and diesel engines still power most vehicles and look poised to be with us for some time to come, even if their dominance is waning. Any engine that develops its power from burning fuel depends on vast amounts of air for the combustion process and efficient operation.

Running under typical circumstances, your car’s engine sucks in anywhere from 150 to 400 cubic meters of air every hour. When you suck in that much air, you get abrasive particulate matter (science for "dirt") that can, over time, accelerate engine wear. Causing parts like bearings, cylinder walls, and piston rings to fail prematurely. To help stop that wear, cars are equipped with engine air filters to trap dirt and particulate matter before they get inside the engine.

Changing your air filter as scheduled is crucial to making your engine live longer and run right. Here, we clear the air (so to speak) about what engine air filters do, what they’re made of, how often they should be replaced—and how you can save a few bucks by replacing them yourself.

An engine air filter is a device placed in an engine’s intake system which is designed to separate particulates from the air before it reaches the engine, where it can cause damage.

Engine air filters aren’t to be confused with cabin air filters which are part of the HVAC system; their job is to clean the air within the car's passenger compartment. Cabin air filters often look like engine air filters and use similar technology.

Various materials are used as filter media, sometimes on their own or in combination. Here are a few examples of the most common filter media materials.

Cellulose

Easily the most common filter material, cellulose is what comprises the hard exterior of plants’ cellular walls and is well-known as the material most paper is made of. Cellulose air filter media is essentially a specialized form of paper that allows air to pass through while collecting atmospheric particulate matter. Sometimes, nanofibers or other materials are used in conjunction with cellulose to improve effectiveness.

Cotton

Cotton is also used in engine air filtration, notably for performance-oriented filters like those produced by K&N. In these applications, layers of cotton gauze are sandwiched between wire screen for strength, pleated, and sprayed with a special, tacky oil that traps particulates.

Foam

Foam air filters are common on gasoline-powered lawn and garden implements and for high-performance and off-road automotive applications. They aren’t usually specified as OEM or OEM replacement.

Polyester and Other Synthetics

Synthetic fibers are also used in air filter media. Sometimes in conjunction with cellulose or on their own, often as non-woven fabric filter media. Some manufacturers have been working with so-called nanofibers, which are incredibly tiny and spun with different surface profiles to make them very efficient as filter media.

When your car’s engine runs, it draws air through its induction system; the air filter is part of that system. Air passes through the air filter, and suspended particulates adhere to the filter media through the action of separation mechanisms. A separation mechanism simply refers to how dirt “gets stuck” in the filter.

The efficiency of an air filter is expressed as a percentage which is usually determined by allowing a known quantity of test dust to pass through the filter over a given period of time, then measuring the difference. i.e., if air laced with 100 grams of dust is allowed to pass through a filter, and 99 grams become trapped while 1 gram passes through, that filter would be said to be 99% efficient. This is an oversimplification but serves to illustrate the concept.

Whatever the factory recommended air filter service interval for your engine, you should check the air filter physically a couple of times a year, or every 7,000 to 10,000 miles. If you drive in particularly arduous conditions, such as areas that are very dusty, you should check your engine air filter more frequently.

Some vehicles will display information about air filter life on the dashboard through the driver information center. Others may have a mechanical device located under the hood on the airbox, which shows airflow restriction. These usually look like a small, clear plastic canister with colored markings and a plunger that indicates the approximate efficiency of the air filter. After you replace the filter, it can be reset. Note that not all vehicles have an air filter life indicator.

Open the filter housing and remove the air filter element as described below. If the design of your air filter allows, gently spread the pleated filter media apart and check for debris. If debris is accumulating and the filter media looks very soiled, it’s probably time to replace the filter. As noted earlier, a dirty air filter might reveal itself through reduced engine performance; ideally, you will have replaced it before it gets to that point.

Engine air filters should generally be replaced every 15,000 to 30,000 miles or as recommended by your owner’s manual. Some filter manufacturers recommend doing so every 12,000 miles, but they have a vested interest in selling more filters.

Vehicles that operate in extremely dusty conditions may need their engine air filters replaced more frequently. Trucks, which are more likely to work in dusty conditions, often have a cyclonic pre-filter that doesn’t need to be replaced but may occasionally need to be cleaned. It’s integral to the air intake, and it uses airflow to remove some particulates from the air before it reaches the air filter element. These pre-filters help to extend the service life of the replaceable air filter element.

As mentioned elsewhere in this article, the primary reason cars have engine air filters is to protect internal components from the damaging effects of particulates that are suspended in the air. Particulate matter consists primarily of mineral dust, which has many sources, both natural or as the result of human activity, and much of it is silica. Silica particulates with a Mohs hardness of 7 or more are the most damaging to engine components.

If you fail to replace your engine air filter, it will continue to collect particulate matter until it can no longer pass enough air to meet the engine's requirements. At that point, performance will deteriorate, and acceleration will suffer.

What won't happen (unless you're driving a carbureted car) is a decrease in fuel economy. The reasons for this are explained in detail below.

This editor’s grandfather owned and operated an auto parts store for 50 years, and he was a stickler for fuel economy. He’d pull a fresh Fram air filter off the shelf for his truck every 15,000 miles or so because he understood that a dirty, clogged air filter would result in wasted fuel—except grandpa was wrong, sort of.

Grandpa would’ve been most familiar with old-fashioned carbureted vehicles, and with those, a clogged air filter can indeed reduce fuel economy by anywhere from 1-15%, in some cases, more; this is because the carburetor that mixes fuel and air for combustion is a mechanical device; it cannot compensate for a clogged air filter.

Thus, when the air filter is obstructed, the carburetor adds the same amount of fuel to a smaller air volume, resulting in an overly-rich mixture that won’t combust efficiently. A common telltale was partially-burned fuel exiting the tailpipe as black smoke. However, the last new cars on the U.S. market equipped with carburetors were sold over 30 years ago, and even then, they were an anachronism.

Electronic fuel injection has displaced the carburetor on essentially all gasoline-fueled passenger vehicles everywhere, and it can adjust for a restricted air filter. Electronic fuel injection measures the amount of air entering the engine both before and after the air filter; the system’s computer can use these and other data to ensure that the ratio of fuel to air is kept as close to ideal for given running conditions as possible.

Let’s say your engine air filter is clogged to the point that it will only allow sufficient airflow for your engine to propel the car at 45 mph. The fuel injection will still supply the correct amount of fuel for that level of airflow, and no more. But a carburetor would simply continue dumping gas down the intake as if the air filter was new.

As a result, fuel economy remains constant with the fuel-injected car even as the air filter becomes partially clogged. This doesn’t mean you should never change your air filter; eventually, air flow would become restricted to the point that engine performance would be adversely affected. This condition will manifest itself with poor acceleration and reduced top speed.

As counterintuitive as it might be to think that an air filter clogged to the point of reducing engine performance wouldn’t affect fuel consumption, it’s true and has been demonstrated in tests performed by the Oak Ridge National Laboratory. Testing with diesel engines yielded similar conclusions.

Nevertheless, grandpa’s point of view persists in the popular imagination, largely because of experiences from the days of the carburetor.

Even the least mechanically inclined person can renew their car’s engine air filter. If you feel comfortable swapping a vacuum cleaner bag, consider yourself sufficiently experienced to handle the job.

Before beginning, purchase a replacement air filter. You’ll need some information about your vehicle to ensure you get the correct part. Whether you buy online or at a brick-and-mortar retailer, you’ll need to know your car’s make, model year, and details about the engine; e.g., inline four-cylinder or V6 (frequently, the same model vehicle will be available with different powertrains, and they don’t necessarily use the same air filter).

If you’re not certain about those details, all cars built since 1981 have a standard, 17-digit Vehicle Identification Number (VIN), which encodes important details about the vehicle. Simply Google searching that number will yield the information you need to order the correct air filter for your car. Alternatively, many auto parts suppliers give the option of providing a VIN when ordering parts to ensure the correct fit.

You can find a vehicle’s VIN plate at the base of the windshield, on the driver’s side, under the glass; it’s also duplicated on a build sticker that’s usually located on the driver’s door or door jamb.

You should consider wearing gloves for this job because engine compartments can be dirty places and may potentially expose you to hazardous materials.

2. Open the filter housing/airbox: this procedure differs from one vehicle to the next; many use metal spring clips and are very easy to open. Simply pop the clips off and separate the halves of the air box, revealing the air filter within. With others, it’s not so obvious. Our Fiat 500 Abarth’s airbox is held together with screws. Occasionally, you may also need to remove air ducts from the filter housing to separate it and replace the filter. It should be fairly obvious if this is the case with your vehicle. More often than not, the ducts will fasten with hose clamps. Loosen the hose clamps and gently but firmly tug and wiggle the ducts till they detach. If you really find yourself stumped here, consult your owner’s manual or take a crash course on your car at YouTube University; just apply common sense when doing so. The problem with the internet is that anyone can use it, even people who pass on bad advice.

3. Remove the filter: with the airbox separated, the filter should be easy to spot. If it’s not, make sure you’ve opened up the right part of your car! Note how the old filter fits in the airbox before removing it; this will assist you when you position the replacement. Then gently remove the filter using your hands (it’s a good idea to wear gloves when servicing vehicles).

January 20, 2023: Updated product links.

August 24, 2022: The article received a major update, with all how-to and informational sections being rewritten. The following products were removed: EPauto, Mann, Toyota Genuine Parts, AC Delco, and Genuine Subarus air cleaners. Wix was added as the No. 1 pick, K&N was moved to No 2, Fram Extra Guard was moved to No. 3, Purolator was moved to No. 4, Bosch Workshop was added as No. 5, and EcoGard was moved to No. 6.

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