Every mechanical component of today’s cars, trucks and SUVs has one common enemy: dirt. Whether produced internally by the combustion process or brought in from outside, dirt is the number one cause of engine breakdown. Effective filtration plays a key role in preventing unnecessary wear and premature failure. Modern filters are more effective than ever when it comes to preventing damage to the engine, fuel system and automatic transmission, however, they are only effective when replaced on a regular basis.

By keeping an adequate stock of popular filters and related supplies, you boost your ability to profit from the preventive maintenance market.

Air Filters
Between 10,000 and 12,000 gallons of air are needed for today’s cars and trucks to efficiently burn one gallon of gasoline. Dirt equivalent to the size of two aspirin tablets within that air will cause the same amount of wear as 75,000 miles of normal driving. With that in mind, it’s easy to see just how important air filters are.

Without a quality air filter, dirt, road grit and other debris can "sand blast" internal engine parts, carburetors and fuel injectors.

Air filters are usually of one of two designs. On most carbureted engines, the air filter is round and fits inside an air cleaner assembly. These round-style filters are made of a top and bottom seal, a mesh screen and a filter media. On fuel-injected applications, the air filter is of a flat, or panel, design and usually fits inside a plastic housing. With either style, a duct directs outside air to the filter. Once the air is filtered, it passes on to the fuel system and combustion chambers.

Two-Stage Design
Most air filters make use of a "two-stage" design. Basically, this is like having two air filters in one. The first stage, generally a foam filter, captures larger particles. The second stage is the paper filter media. This media filters out the smaller particles and prevents them from damaging the fuel injectors, carburetor or cylinder walls. When replaced on a proper schedule, a good, high-quality air filter should remove 98% or more of the sand, road grit and dirt that comes along.

Air filters should usually be replaced every 30,000 miles as part of regularly scheduled preventive maintenance. Holding an air filter up to a light and comparing it with a new one can give you a fairly accurate view of how loaded with dirt it has become. Any filter that appears to be loaded with dirt should be replaced regardless of the odometer reading, as should any filter that is damaged.

Another thing to keep in mind is that no matter how good an air filter is, it can’t do its job if it’s being bypassed. On carbureted engines, the paper gasket at the base of the carburetor can leak and allow air to bypass the filter. Leaking vacuum lines on either carbureted or fuel-injected applications can suck unfiltered air into the engine. Check for such leaks whenever an air filter is being replaced.

Oil Filters
At 40 mph, just over 200 gallons of oil flow through an engine every 60 minutes. After 3,000 miles, the four or five quarts of oil in today’s cars pass through the engine 15,000 times. If the oil is contaminated, that’s 15,000 chances to cause damage to the main bearings, camshafts, crankshafts and numerous other internal engine parts. A neglected oil filter is a sure way to kill an engine.

The vast majority of today’s oil filters are of a full-flow filtration spin-on design. These filters are made of a pleated paper (or synthetic) media, which surrounds an inlet tube encased in a metal housing. The efficiency, amount and type of media used determines the quality of the filter.

On most modern vehicles the oil flows through the pickup screen and then to the oil pump. From there, the oil is forced under pressure into the main oil gallery. A pressure-regulating valve maintains between 20 and 60 psi in the system. Then, the oil flows through the oil filter and on to the moving parts of the engine.

Neglected long enough, an oil filter will become clogged, but this doesn’t mean the engine will be oil-deprived. A bypass valve in the oil filter will open when the pressure deferential between the filter’s inlet and outlet reaches a factory-set level. While it’s true the engine won’t be starved for oil, the oil it receives once the bypass valve opens is completely unfiltered. And if the oil has been in place long enough to clog the filter, it is likely to be filled with engine-damaging dirt and debris.

There has been some debate over how often oil and oil filters should be changed. Under ideal conditions, today’s cars could probably go nearly 7,500 miles between oil and filter changes without ill effects. But ideal conditions are extremely rare. Also under debate is whether or not an oil filter needs to be replaced with each and every oil change. Again, under ideal conditions, the filter probably doesn’t need to be replaced with each oil change.

One thing is for certain: Replacing your oil and filter every three months or 3,000 miles will keep premature wear to a minimum. Compared to the price of an engine overhaul or a rebuilt engine, frequent oil and filter changes more than pay for themselves.

Fuel Filters
Contaminants in cheap gas, flakes of rust from inside the fuel tank and particles of rubber worn from the fuel line can clog fuel injectors or carburetor circuits. A clean fuel supply is dependent on the fuel filter, which removes such contaminants. When a fuel filter becomes clogged, hard starting, hesitation, poor acceleration, stalling and rough idling can result. Clogged fuel filters also cause fuel pumps to work harder and can result in their premature demise.

There are two types of fuel filters. With most fuel-injected cars an inline filter is mounted somewhere in the fuel line between the fuel tank and the fuel rail. With carbureted vehicles an internal filter is most often used. Internal filters usually fit inside the carburetor fuel inlet at the base of the carburetor.

Make sure you sell your customer the correct filter for the application. The media in a fuel filter may be treated paper, a blend of cellulose and synthetic fibers, sintered bronze, a ceramic material or a fine nylon mesh.

Fuel filter life is impacted greatly by the quality of the fuel being used and by the quality of the fuel system components. Cheap gas and bargain fuel hoses are likely to result in a quick clog of the fuel filter.

The standard OEM recommendation for fuel filter replacement is every 30,000 miles. Some professional technicians, however, recommend a yearly fuel filter change as protection against fuel system problems.

PCV Inlet Filters
On many vehicles a small filter can be found between the PCV (positive crankcase ventilation) valve and the PCV valve’s inlet hose. This filter removes dirt that could be pulled into the engine by the vacuum created by normal PCV valve operation.

The PCV valve and the breather filter are vital in both reducing vehicle emissions and prolonging the life of the engine. A plugged breather filter can result in damaging acid and sludge forming within the engine. This acid and sludge, if not removed by frequent oil changes, decreases the amount of lubrication the engine’s moving parts receive, resulting in faster engine wear. The breather filter, as well at the PCV valve itself, should be replaced yearly.

ATF Filters
According to the Automatic Transmission Rebuilders Association, almost nine-out-of-10 automatic transmission failures are due to overheating and fluid contamination. Many owner’s manuals suggest a change of automatic transmission fluid at 100,000 miles, if at all. A transmission should be serviced at least every 30,000 miles and many professional transmission rebuilders recommend yearly fluid and filter changes, especially if the vehicle is used for towing or hauling.

Like motor oil, automatic transmission fluid (ATF) suffers from heat, friction and electrochemical breakdown. Once this process starts, sludge and varnish begin to form within the transmission. At the same time, bits of friction material may be floating in the ATF and clogging the filter. Unlike oil filters, ATF filters do not have a bypass valve. When they clog, the transmission is starved for lubrication. A clogged filter can cause shifting problems or produce a whining sound.

To replace an ATF filter, the pan must be removed and the inside of the pan should be inspected. A small amount of friction material in the pan is normal, but a large amount of friction material or metal particles indicate a potential problem.

In most late-model applications, the ATF filter is a made of polyester felt capable of removing particles as small as 60 microns. With older applications the filter may be a reusable metal screen. Transmission filters usually come as part of an automatic transmission filter kit, which includes a new pan gasket or O-ring. If replacing a filter, make sure to recommend the necessary gasket or O-ring to your customer, as well.

Regular replacement of these major filters is sure to extend the life of any vehicle. Scheduled filter replacement also allows you to regularly inspect your customers’ vehicles to locate any potential repair needs, leading to more potential sales.