Air filter technology

Bob Weber and Dan Pike
Posted on June 3, 2014
There’s more to a filter than meets the eye. The type of media used substantially affects the filter’s performance.
There’s more to a filter than meets the eye. The type of media used substantially affects the filter’s performance.

To operate at peak efficiency, vehicles need clean filters to prevent contaminants from entering fuel, engine or air conditioning systems. Particles can cause poor performance and shorten the lifespan of the vehicle.

When these filters should be replaced depends on many factors, such as vehicle maker’s recommendations and the environment in which the filter operates. Therefore, routine inspection of the filters’ condition is crucial.

The following article on filters was compiled by Bob Weber, a contributing writer for our sister publication, Auto Service Professional, and written by Dan Pike, group executive, Filter Manufacturers Council (FMC) and vice president, membership and members services, Automotive Aftermarket Suppliers Association.

It’s time to clear the air about filters — those automotive components which keep your customers’ vehicles running clean. Here is a brief overview of motor vehicle filtration products, which include filters for the engine, oil, cabin air and transmission.

Filters: It’s what’s inside that counts

Any discussion of motor vehicle filters begins with filter media — the material inside the filter which captures dirt and foreign particles.

Filter manufacturers use many different types of media for various fluids and environmental extremes. The most common used filter media are cellulose-based and glass.

Cellulose media is manufactured with fibers of various sizes. On the top layer of the media, the fibers are fluffed up, rather than compacted down. When fluid and contaminants pass through the media, many particles collect on the fluffy fibers on the surface and don’t travel further into the filter.

Glass media was developed to be utilized in hydraulic systems because it has low flow restriction at high filtration efficiencies. These low-flow resistance properties are beneficial in hydraulics where cold oil is being forced through the media and when filtration in the 3 to 5 micron range is desired.

Glass media has a drawback regarding capacity. Typically, glass media has the same pore size and same fiber diameter through the entire sheet. The media can be manufactured to be very efficient, but then it is so tight that it has very little life or capacity.

Synthetic media is making inroads in replacement filters. In most lube, fuel and air filter applications, cellulose media remains the better choice. As with glass, the reason largely relates to capacity, or filter life. A brief description of the filtering process illustrates this. The process of fluids and contaminants collecting on the fluffy fibers of cellulose filter’s surface is called “adsorption.” The particles adhere to the surface fibers and don’t travel farther into the filter.

The more adsorption a media applies, the more small particles can be separated before they reach the small pore spaces on the screen side of the media. This keeps these small particles from plugging the media.

Cellulose media typically is thicker than synthetic. The thicker the media is, the more time the particles spend traveling through it.

Each time the fluid changes direction around a fiber, the momentum keeps particles traveling in the same direction they were going and they are driven into the fibers.

This particle separation is called “impingement.” As with adsorption, the more impingement that a media applies, the more particles are separated without plugging the tight pore space on the screen side.

Synthetic media does separate some particles with adsorption and impingement, but the smooth fibers can’t hold the particles in place. Often they are washed off with the fluid traveling through the media.

Synthetic media primarily uses the particle separation technique called “direct interception.” Direct interception is simply separating particles by passing the fluid through pore spaces that are small enough to catch them. However, once all pores are filled with the contaminant, the filter is plugged and its life is over.

Because cellulose media is better at adsorption and impingement, it can remove more contaminants than glass or synthetic media without plugging pore spaces.

Can a synthetic media be created with the benefits of cellulose media? This remains to be seen. For now, both cellulose-based media and glass media have a place in today’s filter market.

Keep your customer’s car running clean: Oil filters

Of all the many filters on their vehicles, car owners are most familiar with the oil filter. To become your customer’s valued partner in keeping his or her vehicle in top condition, it’s important that you educate them on the importance of regular oil and filter changes.

You probably will encounter some common questions from your customers regarding their cars’ filters. The most common among new car owners is likely to involve the car’s warranty.

Many consumers mistakenly believe that installing an aftermarket filter on their new car will void its warranty.

 This is your opportunity to inform your customers about their right to have their vehicle serviced at the repair facility of their choice and about the federal laws, such as the Magnuson-Moss Warranty Act, which protect their right to choose. (You can learn more from the FMC Technical Service Bulletin 85-1R2.)

Another common question is about the quality of aftermarket filters, and whether they are as good as original equipment (OE) filters. You can assure your customers the full service manufacturers who make name brand, quality replacement filters design and manufacture their products to meet or exceed the requirements for OE filters. The use of an aftermarket filter will not affect the service intervals recommended by the carmaker.

Breathing easier in the car: Cabin air filters

Less familiar to most consumers are cabin air filters — another opportunity for you to educate your customers. Inform them that these important filters offer protection from outside air for the occupants by stopping allergens, dust, soot and bacteria from entering their car.

Cabin air filters should be changed every 12,000 to 15,000 miles or once a year. Your customers will like the fact that cabin air filter replacement generally takes less than 15 minutes and can easily be scheduled along with other regular maintenance tasks.

You also can inform your customers about “combi cabin air filters,” which contain activated charcoal. Not only do they capture airborne contaminants, combi filters also prevent outside odors from entering the passenger compartment.

Educate your customers that cabin air replacement should be a regular part of their vehicle maintenance routine. Clean cabin air filters help keep their vehicle’s heating, venting and air conditioning systems running efficiently by keeping these systems free from contaminants.  Replacing these filters is also important to your customer’s health and the health of their passengers. Let your customer know that contaminates inside a vehicle can be as much as six times higher than the levels outside the vehicle — so a clean cabin air filter will help them breathe easier in their car!

Non-serviceable transmission filters

Automatic transmissions have become more complex. Once controlled by vacuum, modern transmissions have been transformed into computer command centers made up of various solenoids and other electronics that control the operation of the transmission.

New technology brings changes to transmission filter service maintenance. Some manufacturers require literally no scheduled maintenance.

Several auto manufacturers have no scheduled maintenance until the vehicle has 100,000 miles on the drive train.

Non-serviceable transmission filters were introduced in the 1970s. Almost every manufacturer now has a transmission that is non-serviceable. Caution and care must always be taken when replacing any transmission filter. The non-serviceable ones require extreme scrutiny. Almost every automatic transmission has a filter that could be replaced.

The term non-serviceable means that a partial or total disassembly of the transmission and other related internal parts is required for filter service. Non-serviceable transmission filters typically consist of four different styles.

The first style is one that does not have the traditional pan. The transmission case consists of two pieces split vertically. For any internal repairs (including filter replacement) the transmission needs to be removed and disassembled into the two halves.

The second style has a primary filter located internally and one or more secondary filters accessible through a gasket sealed pan. Replacing the primary filter would require partial or total disassembly of the transmission.

The third style has the primary filter located internally, and an external accessible filter. Two examples would be either an external spin on or a cooler line style filter. Replacing the primary filter, would require partial or total disassembly of the transmission.

The fourth style also contains a pan and gasket. Special circumstances are attached to this filter replacement. A valve body or other parts may need removal with the filter. Sometimes this type may appear simple to an inexperienced individual trying to change the filter.

Many problems could occur when attempting to change the filter. Loose nuts, mis-adjustment, and internal component damages are just a few of the problems associated with servicing this type of transmission. Attempting to change the filter on this type of transmission could lead to a shorter life of the transmission, a premature break down, or a major overhaul.

Before changing any transmission filter, (especially late models) always refer to the instructions when included in the kit or the manufacturer’s service manual for proper filter service.

The ‘big stuff:’ Heavy-duty filters

Heavy-duty or commercial vehicles contain many more filter applications than passenger vehicles, each with their own criteria and service intervals. The FMC Web site includes resources for these heavy-duty applications. Included is information, technical service bulletins and frequently asked questions about heavy-duty air filters, diesel fuel filters, oil filters, coolant filters and hydraulic filters.

Filters and the environment

Keeping used oil filters out of landfills protects the environment and provides a valuable resource for recycling.

The FMC website includes used oil filter recycling resources. Information includes:

• Environmental and educational resources: information about choosing a filter management service, plus proper methods for recycling filters at the shop and at home.

• Recycling equipment: contact information for oil filter recovery system, crusher, spinner and shredder businesses.

• Recycling filters at the shop: recycling used oil filters in an professional shop setting.

• Choosing a filter management service: detailed information about choosing a filter management service.

• Step-by-step instructions for proper hot draining.   ■

About the Filter Manufacturers Council

Since 1971, the Filter Manufacturers Council (FMC) has represented North American manufacturers of vehicular and industrial filtration products. Its website,, has a wealth of information for you as a service professional. You not only will find information to assist you in diagnosing and repairing filter-related problems, you’ll also find materials to help you educate your customers about their cars’ filters as well as resources to help you recycle used oil filters.


Filter replacement aids vehicles and drivers

According to the Car Care Council, of the vehicles inspected during last year’s National Car Care Month, air filters were one of the top three problem areas. Seventy-nine percent of vehicles inspected were in need of service or repair, and the top problem areas were engine oil (22%), brakes (20%) and air filters (17%). Results of this year’s National Car Care Month (April) are pending.

Website reports, “Replacing a clogged air filter on an older vehicle with a carbureted engine can improve both fuel economy and acceleration by a few percent under normal replacement conditions.

“On fuel-injected, computer-controlled gasoline engines — such as those manufactured from the early 1980s to the present — or diesel engines does not improve fuel economy, but it can improve acceleration.”

As for cabin air filters, the Car Care Council urges consumers to have them replaced every 12,000 to 15,000 miles, or per the owner’s manual. “A dirty or clogged cabin air filter can cause contaminants to become so concentrated in the cabin that passengers actually breathe in more fumes and particles when riding in the car than when walking down the street,” says Rich White, executive director.

“A restricted cabin air filter can cause musty odors in the vehicle and impair airflow in the heating, ventilating and air-conditioning (HVAC) system, possibly causing interior heating and cooling problems,” White points out. “Over time, the heater and air conditioner may also become damaged by corrosion. In addition to trapping pollen, bacteria, dust and exhaust gases, the cabin air filter prevents leaves, bugs and other debris from entering the HVAC system.”

To read the entire May 2014 issue of Modern Tire Dealer, see our digital version by clicking here!

Related Topics: Bob Weber, Cabin Air Filters, Dan Pike, Filter Manufacturers Council, filters, oil filters

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Bob Ulrich was named Modern Tire Dealer editor in August 2000. He joined the magazine in 1985 as assistant editor, and has been responsible for gathering statistical information for MTD's "Facts Issue" since 1993.
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