There are four major filters: oil, fuel, coolant and air, each with different strengths and capacities.
Fluid contamination is the cause of 70 percent of equipment failures, including engine, transmission and hydraulic system, according to several Society of Automotive Engineers (SAE), Warrendale, Pa., technical papers.
Consequently, the purpose of the filter is to protect the engine from damaging contaminants.
Contaminants are ingested with the fuel, air or oil; built-in during engine assembly; or created as the engine runs.
Many users claim that most engine-wear is caused by abrasive particles that are several times smaller than those trapped by a full-flow filter. One study shows that soot as small as 2-micron particles are destructive, can wear away the engine's internal parts and deplete the oil's additive package.
The most damaging contaminants are in the 5-micron to 20-micron range, which are too small for the standard OEM filter to remove.
The major contaminants in diesel engines are soot, dust or dirt (silicon), anti-freeze and wear metals. New engines have thousands of very fine particles that break off and end up in the oil. If these and the work-hardened particles generated during break-in become embedded in the softer bearing surfaces, they remain and continue to generate more particles. Consequently, consider installing a bypass filter, which separates debris as small as 1/10-micron particles from the oil.
Typically, fuel filters usually come in pairs, primary and secondary. However, some systems operate only with a single filter. Others depend on a fuel filter and on an optional fuel/water separator.
Primary filters are more open to capture large particles and protect the transfer pump from abrasives. Secondary filters capture small particles and are designed to protect the injection pump.
Currently, filter manufacturers are refining fuel filters to meet today's engine design changes. For example, with electronic engines' higher fuel-injection pressures, some filters have reduced their requirements down to 10 microns and some to 5 microns.
Cummins, Columbus, Ind., recommends coolant filters be changed at every oil/filter change unless the DCA4 concentration level is more than three units. The supplemental coolant additive must be tested every six months.
When changing the coolant filter, before installing the new filter, apply a light film of lubricating oil to the gasket sealing surface. Mechanical overtightening of the filter can distort the threads or damage the head. Consequently, the filter should be installed on the head and turned until the gasket contacts the filter head surface. Then, it should be tightened an additional ½ to ¾ of a turn, or as specified by the manufacturer.
For efficient combustion, a modern diesel requires several thousand times as much 100 percent clean air as it does fuel.
The size of the air filter is the result of balancing:
The air flow the engine needs for efficient combustion;
The restriction (resistance to air flow), which will be caused by the filter; and
The dirt the filter will need to hold to allow for a practical change interval.
Most engine manufacturers specify that a new filter must trap at least 98.5 percent of all airborne dirt. Filter efficiency improves as the “dust cake” builds up on the surface of the media.
Restriction gauges, which measure dirt buildup, are used as part of a filter maintenance program. Until maximum acceptable restriction is reached, the accumulation of dirt in the filter actually adds to its efficiency.
Air filters generally last one year — even if the restriction gauge still is at an acceptable level. Filter media can deteriorate due to moisture, vibration, flexing and temperature changes. Loss of power is not necessarily a symptom of a restricted air filter. Changes in the density of the outside air (i.e. when operating at high altitudes or in high outside temperatures) can create the same effect.
An air cleaner's life depends on its working environment. For example, snow or exhaust smoke can plug an element in a very short time. The only reliable way to determine if your air filter is OK is by using a restriction gauge.
If the restriction gauge has an abnormally high reading after the air filter element is replaced, the intake system may be plugged ahead of the air cleaner. Check inlet screens, damaged rain caps or ducts that could be plugged.
To protect your filter, cover the air filter intake and tie down the exhaust cover before the unit is washed or transported. Always change filters in a protected area, limiting the chance of dirt being blown into the engine intake.
Bob Deierlein is Waste Age's truck editor.