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Automotive experts agree dirt is the number one cause of engine wear. In fact, a recent analysis by Federal-Mogul Corporation reports that 43.4 percent of all engine bearing distress is caused by dirt.

Dirt particles are extremely abrasive. They consist of razor-like flakes of road dust and airborne grit drawn into the engine through the intake manifold.

Engine Air Filtration is the key to preventing potentially costly engine repairs caused by dirt and other airborne particles. The Air Filter removes these various contaminants by trapping and holding them outside the system of oil circulation.

An engine "breathes" air to mix with fuel for combustion - about 9,000 gallons of air for every gallon of gas. The air within one cubic mile over a typical city contains more than 400 tons of suspended dirt, and the concentration is much higher in rural areas where travel frequently is over unpaved roads.

The Engine Air Filter is the first line of defense against abrasive airborne grit. It must effectively filter harmful contaminants - such as insects, vegetable matter, dirt, sand, dust, leaves and fine straw - without obstructing the vital flow of air that sustains the engine.

Conventional Engine Air Filters quickly become obstructed with dirt, reducing vital engine air intake, leading to poor engine performance and low fuel efficiency. They require frequent replacement.

High-quality, Premium Engine Air Filters - especially those with a synthetic nanofiber layer (see 3rd image below) - are better constructed than conventional filters, remove more contaminants from the air, and also provide less airflow restriction.

Not only do synthetic filters have a higher filtration efficiency, but they also have a larger dirt holding capacity. (See images 1 & 2 below.)

Whether it is in the vehicle’s engine oil, the engine air, or the fuel system, automotive filtration is basically about removing contaminants that can cause damage and wear to a vehicle’s components.

These contaminants can prevent the free flow of fluids within these systems as well as cause damage. Keeping the oil and air clean and flowing in and around the engine without any debris or obstruction will enable the vehicle to run smoothly and perform better for thousands of miles.

The Engine Air Filter has evolved from rudimentary, often nonexistent, dust protection in early automobiles to sophisticated, high-efficiency, and often pleated paper or synthetic materials in modern vehicles. Its primary function is to protect the engine from abrasive contaminants while ensuring optimal airflow, a challenge that has led to significant innovations over the past century.

There are various types of engine air filters – radial, axial, conical and panel air filters. Radial air filters were in use for the first thirty years after the development of dry pleated paper type air filter. This type of air filter utilized a dry pleated paper (cellulose) type element covered with a wire screen mesh on both the interior and exterior surfaces of the element.

Panel air filters are the most popular type of air filter used in automobile and light truck applications today. Though Purolator developed panel air filters in the 1950s, they did not become popular until the 1980s. This is mainly because vehicles are being built today to be more and more aerodynamic and there is a push to utilize the space under the hood as effectively as possible.

➣ No Initial Filtration: Early automobiles rarely used air filters. Engines breathed unfiltered air, leading to accelerated wear from dust and dirt.

➣ Water Bath Cleaners (1900s to 1930s): Early in the 20th century, water bath cleaners were used for vehicles, tractors, and stationary engines. These worked similarly to oil bath cleaners (see next section below), though they were soon deemed very inefficient. By the 1940s, oil bath designs had displaced water bath designs because of their noticeably superior filtering performance.

➣ Early Improvisations (1930s to 1950s): Even into the 1950s, rudimentary methods were used, such as fastening nonwoven material in front of air intake pipes, a method noted by industry professionals to keep road dust and soot out of the intake.

➣ Performance Shift: By the 1940s, "Oil Bath" Air Cleaners replaced water bath systems, providing much better performance in dusty conditions. These cleaners were very widely used in automotive and small engine applications until the widespread industry adoption of the paper filter in the early 1960s.

An Oil Bath Air Cleaner consists of a sump containing a pool of oil and an insert which is filled with fiber, mesh, foam, or another coarse filter media. The cleaner removes particles by adhering them to the oil-soaked filter media; as opposed to traditional filtration, the openings in the filter media are much larger than the particles that are to be filtered.

When the cleaner is assembled, the media-containing body of the insert sits a short distance above the surface of the oil pool. The rim of the insert overlaps the rim of the sump. This arrangement forms a labyrinthine path through which the air must travel in a series of "U-turns": first up through the gap between the rims of the insert and the sump, then down through the gap between the outer wall of the insert and the inner wall of the sump, and then finally up through the filter media in the body of the insert.

This U-turn takes the air at high velocity across the surface of the oil pool. Heavier (and typically larger) dust and dirt particles in the air cannot make the turn due to their inertia, so they fall into the oil and settle to the bottom of the base bowl. Lighter (and typically smaller) particles stick to the filtration media in the insert, which is wetted by oil droplets aspirated there by normal airflow. The constant aspiration of oil onto the filter media slowly carries most of the finer trapped particles downward and the oil drips back into the reservoir where the particles accumulate.

Oil Bath Air Cleaners are still used in off-road equipment where very high levels of dust are encountered, for oil bath air cleaners can sequester a great deal of dirt relative to their overall size without loss of filtration efficiency or airflow. However, the liquid oil makes cleaning and servicing such air cleaners messy and inconvenient, they must be relatively large to avoid excessive restriction at high airflow rates, and they tend to increase exhaust emissions of unburned hydrocarbons due to oil aspiration when used on spark-ignition engines.

➣ Wartime Influence: World War II prompted the need for much more robust, heavy-duty, reliable air filtration for military vehicles, which spurred several significant advancements in air filter media.

➣ Disposable Engine Air Filters: The push for convenience and less maintenance led to disposable, paper-based engine air filters, reducing the need for the inconvenient, messy cleaning required by the earlier oil bath systems.

➣ Pleated Paper (Cellulose) Air Filters: The development of resin-impregnated pleated paper allowed for a vast increase in surface area, allowing more air to pass while trapping smaller particles. This highly efficient, affordable technology, perfected in the 1950s, became the standard on most vehicles.

➪ More on Pleated Paper (Cellulose) engine air filter media in the section on "Air Filter Materials". (See below.)

➣ Reusable Engine Air Filters (1969): K&N Engineering introduced a washable and reusable engine air filter designed for high-performance motorcycles, utilizing cotton gauze, which was designed to allow high airflow while protecting the engine in dusty conditions.

➪ More on Cotton Gauze engine air filter media in the section on "Air Filter Materials". (See below.)

➣ Modern Engine Air Filter Materials: Today’s engine air filters often use synthetic fibers or advanced paper blends (cellulose-synthetic blends) to provide improved cleanliness and durability, allowing them to last longer and work better under harsh conditions.

➪ More on Synthetic and Synthetic-blend engine air filter media in the section on "Air Filter Materials". (See below.)

➣ Additional Protection ➔ Pre-Filters: Racers and off-road enthusiasts subject their vehicles to some of the most severe conditions possible. These vehicles operate where heavy dirt and mud that gets slung into every crack and corner, often clogging the regular existing engine air filter.

Pre-Filters fit over the top of the existing engine air filter in order to prevent large particles from sticking to the standard air filter and blocking the flow of air to the engine. These polyester mesh bags feature an industrial grade elastic band at the opening to ensure the pre-filter does not slide off.

These pre-filters are designed to keep larger particles from getting into and clogging the pleats of existing air filters. When an air filter is clogged, the engine loses horsepower and the filter must be cleaned or changed. There is no vacuum or compressed air available on the race track or out in the swamp, but a pre-filter is easily removed and shaken free of debris in seconds. Moreover, they will not cause any significant reduction in air flow.

Pre-Filters are constructed with woven mesh that contains uniformly-sized openings. They are oil-free, so the dirt will not stick to the bag and create a loss of air flow and horsepower. Some pre-filters are treated with a hydrophobic water repellent process that helps prevent moisture from damaging the air filter. This proprietary process is done at the mill as the pre-filters are created, not sprayed on, so there is no loss of air flow. While pre-filters are effective in repelling water, they are not waterproof. They prevent particles down to 0.005 from getting to the air filter without significantly reducing air flow.

➣ Cabin Air Filter Adoption: While engine filters protect the motor, passenger-cabin air filters, also known in the United Kingdom as pollen filters, appeared later, with SAAB introducing them in 1979 and others, like Mercedes-Benz for instance, in the 1980s.

The Cabin Air Filter is typically a pleated-paper air filter placed in the outside-air intake for the vehicle's passenger compartment. Some of these filters are rectangular and similar in shape to the engine air filter. Others are uniquely shaped to fit the available space of particular vehicles' outside-air intakes.

Modern Engine Air Filters serve to keep silicon dioxide (sand) and aluminum oxide (dirt), as well as many other airborne contaminants  - such as insects, vegetable matter, dust, leaves and fine straw - out of the engine combustion chamber, cylinders and motor oil.

Due to the volume of air required to burn a small amount of fuel in modern vehicles (it takes 9,000-10,000 gallons of air to burn a single gallon of fuel), it is crucial to have minimum restriction on the flow of air going into the engine intake. Even a partially restricted engine air filter can significantly affect the performance and reduce the fuel efficiency of the vehicle.

According to the U.S. Department of Energy, replacing a clogged air filter can favorably impact gas mileage by as much as 10 percent.

➣ Protection: Air Filters trap fine particles, ensuring cleaner air intake, which improves engine durability and protects sensitive sensors.

➣ Performance: A clean Engine Air Filter maintains a proper air-fuel mixture, which is crucial for performance and fuel efficiency.

➣ Replacement Cycles: Typical recommended replacement intervals for an engine air filter are around 30,000 to 45,000 miles (48,000 to 72,000 kms), or once a year, although this will vary based on driving conditions. Vehicle owners who drive more often on dirt or gravel roads need to change the engine air filter more often than those who drive mostly on paved roads.

Most fuel injected vehicles (both gasoline and diesel) use a pleated paper (cellulose) engine air filter element in the form of a flat panel. This filter is usually placed inside a plastic box connected to the throttle body with duct work.

Older vehicles that use carburetors or throttle body fuel injection typically use a cylindrical engine air filter, usually between 100 mm (4 in) and 400 mm (16 in) in diameter. This filter is positioned above or beside the carburetor or throttle body, usually in a metal or plastic container which may incorporate ducting to provide cool and/or warm inlet air, and secured with a metal or plastic lid. The overall unit (filter and housing together) is called the air cleaner.

Engine Air Filters can be constructed using a variety of different materials. Here are the most popular ones:

Pleated Paper Air Filter Elements are the nearly exclusive choice for automobile engine air cleaners, because they are efficient, easy to service, and cost-effective. The "paper" term can be somewhat misleading, as the filter media is considerably different from papers used for writing or packaging. The paper is bent in a zig-zag shape and therefore the surface area of the paper is very large, in the range of 50 times that of the air opening.

Cellulose air filter media is a cost-effective, sustainable, and highly efficient material made from processed wood fibers and paper, used widely for engine filtration systems. It offers robust performance, high permeability, and can trap various contaminants through its porous, paper-like, wet-laid structure. It is composed of fibers that create a tortuous path (a matrix of fibers) that captures particles throughout the depth of the material, not just on the surface. It is capable of high-efficiency filtration for dust, dirt, and other air-borne contaminants, and is also more affordable than synthetic or composite alternatives.

Side Note: "Paper" and "cellulose" are often used interchangeably, though advanced engine air filters may also blend cellulose with synthetic fibers for superior moisture and heat resistance, for more extreme conditions, as well as slightly improved airflow.

There is a persistent belief among tuners, fomented by advertising for aftermarket non-paper replacement filters, that paper filters flow poorly and thus restrict engine performance. In fact, as long as a pleated-paper filter is sized appropriately for the airflow volumes encountered in a particular application, such filters present only a trivial restriction to flow until the filter has become significantly clogged with dirt.

Oil-wetted Polyurethane Foam elements are used in some aftermarket replacement automobile air filters. Foam was, in the past, widely used on small engines, lawnmowers and other power equipment, but automotive-type paper filter elements have largely supplanted oil-wetted foam in these applications.

Foam filters are still commonly used on air compressors for air tools up to 5 horsepower (3.7 kW). Depending on the grade and thickness of foam employed, an oil-wetted foam filter element can offer minimal airflow restriction or very high dirt capacity, the latter property making foam filters a popular choice in off-road rallying and other motorsport applications where high levels of dust will be encountered.

Foam Engine Air Filters are capable of holding a lot more dust than pleated paper air filters but they usually require more complex maintenance. However, due to the way dust is captured on foam filters, large amounts may be trapped without measurable change in airflow restriction.

Oiled Cotton Gauze is employed in a growing number of aftermarket automotive air filters marketed as "high-performance" items.

In the past, cotton gauze saw limited use in original-equipment automotive air filters. However, since the introduction of the Abarth SS versions, the Fiat subsidiary supplies cotton gauze air filters as OE filters.

Oiled Cotton Engine Air Filters offer superior airflow (i.e., performance) than pleated paper engine air filters, however, they have a lower filtration efficiency (they capture a lower volume of air-borne contaminants), making them less suited for dusty, daily driving.

Stainless Steel Mesh is another example of a medium which allows more air to pass through. Stainless steel mesh comes with different mesh counts, offering different filtration standards.

In an extremely modified engine lacking the space for a cone-based air filter, some will opt to install a simple stainless steel mesh over the turbo to ensure no particles enter the engine via the turbo.

Synthetic Engine Air Filter media consists of engineered fibers - such as polyester, polypropylene, or nanofibers - designed to provide superior airflow and filtration efficiency compared to traditional cellulose (pleated paper) filters. Unlike cellulose, which is made from natural wood pulp, synthetic media offers a more uniform structure with consistent pore spacing, allowing for better particle distribution throughout the material rather than just on the surface.

Synthetic fibers can capture much smaller particulates (see image below), sometimes down to 2 microns or even down to sub-micron levels, providing enhanced engine protection. The aerodynamic shape of synthetic fibers creates less resistance, which can help improve horsepower and throttle response. Synthetic media typically holds its form much better under heavy load (e.g., in racing applications) and can last 2-3 times longer than cellulose media.

Cellulose (pleated paper), oil-wetted cotton gauze and foam filters are larger and have larger spaces between the fibers in the media, causing contaminants to load into the depth of the filter, plugging the airflow path and resulting in higher restriction (see image below).

Conversely, synthetic engine air filters have a lot more pores per square-inch (they have a higher pore density), allowing for much higher dirt-holding capacity and lower pressure drop when compared to the other types of filter media. Their much thinner media fibers produce more uniform pore size distribution, improving the filter's overall ability to capture and retain particles of various sizes, including the very small ones.

Many synthetic filters are "dry" and oil-free, making them washable and reusable for the life of the vehicle. They are generally hydrophobic (water-resistant, literally "afraid of water") and less affected by moisture, heat, or chemicals than cellulose filters, which can weaken or restrict flow when wet.

|➞ Common Synthetic Media Types:

• Polyester/Polypropylene: Frequently used for their rigidity and stability under high operating temperatures.
• Nanofibers: Extremely small fibers applied as a layer to capture the finest dust particles without significantly restricting airflow. Highly efficient media.
• Synthetic Blends: Some manufacturers, such as K&N and AMSOIL's partner Donaldson, blend synthetic fibers with cellulose (paper) fibers to balance cost with improved durability, air flow, and moisture resistance.

➪ Note: AMSOIL carries various Engine Air Filters, as well as Cabin Air Filters, from our partners WIX, MANN-FILTER, and Donaldson.

WIX is well-known around the world for its innovative filtration products for the automotive and light truck market. Founded in 1939, the Gastonia, N.C. company earned acclaim during World War II when it created an oil filter out of a paper tube, wooden plugs and yarn when steel was in short supply.

In 1954 WIX created the revolutionary canister spin-on oil filter that was eventually adopted as original equipment on most vehicles. Today, WIX manufactures some of the best oil, air, lube, cabin air, hydraulic, fuel, crank case breather and transmission filtration products on the market.

The company is also widely known for its support of NASCAR. WIX has been involved with racing and NASCAR for quite a few years now, both as a sponsor and in the race cars themselves. The company’s long-standing relationship with NASCAR not only demonstrates the superior quality of WIX filters, but it also shows their unwavering dedication to racing. Their clear focus on quality makes them a perfect match for AMSOIL.

WIX Panel Element Air Filters have a linear path through the filter for low airflow restriction, a specially formulated adhesive to form WIX’s exclusive pocket pleat for the filter media and a soft sealing urethane gasket molded in place on the filter element.

Radial air filters are constructed of mesh screen on the inside wall diameter for element strength and media protection from backfire. Each round filter is manufactured with heat-resistant plastisol with specially designed crush seals on the top and bottom walls and adhesive seal joining the media ends.

AMSOIL also carries WIX racing filters in addition to filters for more common applications. This includes not only standard engine air and oil filters, but also fuel filters, transmission filters, cabin air filters, as well as those filters specially designed for racing applications.

MANN-FILTER, with its U.S. headquarters in Portage, Michigan, is the world’s largest filter company as well as a worldwide leader in auto, light truck, heavy duty, motorcycle and off-road filtration products. Although they specialize in European vehicles like Audi, BMW, Mercedes, Volkswagen, Porsche, Volvo and Jaguar, they also build various select filters for Ford, GM and Chrysler.

Founded in 1941, MANN+HUMMEL develops and manufactures automotive components such as air filter systems, intake manifold systems, liquid systems and cabin air filters for the original equipment (OE) automotive industry. They also make and sell aftermarket filter elements for vehicle servicing and repair.

MANN-FILTER air filters are known for their high quality build and high delivery capability as well as a product range that covers more than 95 percent of all European models and a select group of U.S. and Asian models in the North American market.

MANN-FILTER air filters feature optimum pleat geometry for maximum dirt holding capacity and high filtration efficiency for engine protection. They also correct air flow, enhancing engine protection. The high quality of the filters offers reliable service throughout the entire service interval.

For over 100 years, Donaldson has been solving customers' complex filtration needs. Today, Donaldson is one of the largest providers of unique filtration technologies and high-quality air filters. On-road or off-road, you can trust Donaldson air filters to withstand whatever the environment throws your way.

Donaldson Endurance heavy duty air filters with exclusive nanofiber technology offer longer engine life, longer filter life, initial efficiency up to 99.99 percent and five times more capacity then conventional air filters. The nanofiber technology causes submicron contaminants to be held on the surface layer of smaller fibers. This filtration characteristic is only possible with this new type of air filtration technology.

In on-highway applications, where the contaminant is primarily submicron in size, Donaldson Endurance filters cause less restriction than conventional filters with cellulose media. The smaller inter-fiber spaces of nanofiber technology have a higher efficiency and capture more contaminant.

The following illustration may help visualize these phenomena: imagine two filters, a chain link fence and a mosquito net, with a tennis ball being a dirt particle. As you may have observed, a tennis ball will fit quite nicely into an opening of a chain link fence, but will obstruct the hole almost 100%.

Now imaging the same tennis ball covering a mosquito net. The tennis ball, at the point of contact with the netting, will obstruct much less filter area than the chain link fence example. In fact, air will flow around the tennis ball all the way to the point of contact. Consequently, it will take many more particles (tennis balls) to obstruct the entire mosquito net surface area than it will to obstruct the entire chain link fence surface.

Donaldson Blue Endurance engine air filters are guaranteed to deliver twice the mileage between filter change intervals over cellulose (pleated paper) air filters for on-highway applications or customers will receive a brand new Endurance engine air filter at no charge.

Donaldson P-Series Engine air filters (see image below) offer premium filtration at a competitive price. P-Series air filter media is made up of specially formulated fibers designed to trap contaminants such as dust, dirt and soot before they reach the engine.

The media is pleated to maximize the air filter's surface area and then placed between rigid liners to provide stability and support. A high quality filter seal is then applied or built-in to the open end of the filter to prevent any dirty air from bypassing the filter.

Genuine Donaldson PowerCore® engine air filters (see images below) provide superior protection and performance over conventional air filters.

Their greater filter capacity means longer filter life, fewer filter changes and less money spent on maintenance. Their lower initial restriction protects engine performance and fuel economy and their reliable, leak-resistant Radial Seal™ technology keeps the filter in place – even under heavy vibration.

PowerCore® engine air filters have been meeting original equipment manufacturer specifications for over 20 years.

Since 1915, Donaldson has pioneered the development of nearly every major advancement in heavy-duty engine air filtration. Nothing else protects, performs and provides longer life for engines than industry-leading Donaldson engine air filters. Donaldson air filter media provide the very best engine protection no matter what the operating conditions. AMSOIL now stocks all of Donaldson's most popular engine air filters.

________ ➪ CLICK HERE to browse our entire selection of AMSOIL, WIX, MANN-FILTER, and Donaldson filters.

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