Don't Bypass
    Bypass Filters

The advice found in the adage "If a little is good, a lot must be better" doesn't apply too often. It most certainly does, however, when it comes to lube oil filtration -- IF you do that filtering properly. Simply adding more filters or finer filters is not the way to achieve better results. Caterpillar advises, "Each engine manufacturer designs a lubrication system to handle the dirt and contaminants generated by that specific engine. Some engines have different needs than others. Filter out too much, and the filter will plug. Filter out too little, and engine wear will increase."

Filters are important
While base oil does not actually wear out, the various additives in the oil can become depleted. And when the additives are gone, the oil will no longer perform effectively.

Filters play an important role in how long you can count on your oil to do its job. Proper filtering prevents a buildup of contaminants that can score bearings, rings and cylinder walls. Contamination also can contribute to an increase in viscosity and gum deposits on rings and valves. Because filtration is necessary for effective engine protection, it is important to make sure you have the best available system in good working order. According to some estimates, 60 percent of the potential causes of wear and failure can be eliminated by well-designed and properly applied filtration systems.

Leon Trimble, president of U.S. Petrolon, a Dallas-based firm that distributes bypass filter systems, described an acceptable system as "one that saves you two or three oil changes by removing wear-causing particles that eat up your engine. Wear is caused by having particles of dirt suspended in the oil that are bigger than the film of oil between moving parts when the equipment is under load."

Figure 1

The amount of flow through a bypass filter is controlled by an orifice in the system which is sized to get a flow of approximately 10 percent of the total pump output.

Table 1 Bypass Filtration Systems The T.F. Hudgins Company, the firm that manufactures the Spinner II bypass filter, has prepared this outline of the various bypass systems available to fleets. Depth element: This is the familiar 750 bypass filter, called that because the canister has a volume of 750 cubic inches. This filter consists of packed cellulose fibers which form a relatively deep maze through which the oil must pass. Dirt is caught within the bulk of the material. [ AMSOIL has a refill which uses its unique stacked disc element that can slip right into this type of bypass filter canister.] Pleated paper element: These can be either remotely mounted or of a spin-on design. The filtering material is made of thin paper which is usually pleated to increase the surface area exposed to the oil. this generally results in a smaler size than the 750 for the same flfow capacity. Stacked disc element: usually a spin-on design, this is a combination of the depth and surface types which uses a relatively thick paper cut in a special pattern to increase surface area. [AMSOIL's unique variation on this form of bypass filter utilizes 1/4 inch thick discs of wood and cotton fiber stacked to provide both surface and full depth filtration. The full depth filtration thickness which provides AMSOIL's unique quality of filtration is 1.25" thick.] Motor driven centrifuge: These large electric motor drive machines costing upwards of ten thousand dollars have been used for years on large engines and turbines in industry and marine applications. Self-powered centrifuge: These small units have the centrifuge bowl driven at high speed by a built-in turbine powered by the pressure of the oil being cleaned.

[In the early 1960s], a move away from the use of bypass filters was made by some engine manufacturers. Full-flow filtering systems grew in popularity. Such systems handle the entire pump output, and are designed to filter out relatively large particles only -- those in the 40 to 60 micron range. A full-flow filter has a low pressure differential across it, and is placed between the oil pump and bearings or other location being lubricated. It provides a very useful function because it removes particles on a continuous basis.

Like some other engine suppliers, Cummins recommends that both bypass and full flow-filters be used. This is the system depicted in Figure 2. Such a design provides the lowest overall user cost because of the double protection against wear. The combination protects engines from catastrophic events by filtering all lubricant flowing through the system. Very fine abrasive particles also are removed by the bypass filter.

Tests support bypass systems
Studies at the Cummins Technical Center using various size contaminant particles in an unfiltered NTC 335 engine indicated that particles above five microns cause the most wear problems. This suggests that a filtering system removing particles in the five micron range could minimize bearing and ring wear. These five micron particles are indeed removed by a bypass filter[, but not by full-flow filtration alone].

Click on Graph to Enlarge

Figure 2

Results of tests with various filtering systems were also performed. The data were obtained by adding fine test dust samples to an engine sump and checking various filtration systems. These studies indicate that wear can be reduced by up to 91 percent as a result of using a bypass filter in combination with a full-flow design.

Another study was made using dump trucks under normal operating conditions. Of course, no dirt was added to the oil sump for this test. The test vehicles, each having 40 micron full-flow filters, were run 120,000 miles, and subjected to normal maintenance procedures. Test results show that piston ring wear was reduced seven to 63 percent and bearing wear 30 to 64 percent as a result of adding a bypass filter. A number of bypass filtration systems are outlined in Table 1.

Filter maintenance
In answer to the question "Does an engine's age affect the filter?" Caterpillar says, "Yes." For example, as an engine ages more and more, blowby compression gas passes into the crankcase. This gas carries carbon from combustion, which is removed by the filter. The older the engine gets, the more carbon must be removed. [Don't put off adding a by-pass filter because an engine has higher mileage. This is when the engine needs the added protection the most.] Some suggestions from Baldwin Filters on the topic are outlined in Table 2.

Table 2 Filter Change Tips The Baldwin Filter people offer these suggestions for you to follow when making filter changes. On element-type filters, be very careful not to put sideways pressure on the filter cartridge when you are removing the housing cover or old filter element. Wipe out the housing to make sure no dirt enters the system. Make sure that no part of the old gasket remains on the housing. A filter that leaks because it's not sealed properly cannot be expected to filter effectively. On 750- and 500-size housings, clean and inspect the T-handle assemply. If you disassemble it to replace the seal, be sure to re-assemble it properly. After installing a new element, use a new gasket on the housing lid. Lubricate the gasket of a spin-on filter before installing it. The most important step in changing filters - check to make certain the filter has sealed. No matter how good the filter, if it is not sealed, it will not work! Check it before and after adding new oil.

Sudden or gradual decreases in engine oil pressure usually indicate a plugged filter. "The major cause of filter plugging," according to Larry Rupert, director of research and development for Baldwin, "is an instability in the engine oil additive. Additive precipitation generally occurs in the presence of water or coolant."

Coolant can leak into the oil at almost any point in the system, and water generally enters through condensation -- typically while idling at cold temperatures.

"when someone has a filter that becomes plugged with additive precipitation early in its life, he replaces the filter -- usually with another brand -- and that filter often goes on through a normal life cycle without plugging. The conclusion is that there was something wrong with the first filter," says Rupert.

Actually the first filter was just doing its job by removing the additive gel. The real problem is within the engine, or with how the engine is used. Either situation can be diagnosed by inspection. [Oil Analysis will identify this problem often before damage occurs and alerts you to likely sources of the problem.]

Paper filters that have removed water or coolant contamination usually are gray in appearance and have wavy pleats. There may be a gel-like coating on the surface or, in severe cases, a shiny black sludge covers the element.

Blowby in an older or badly worn engine will eventually overpower the dispersants within the oil and plug the filter. In such cases, oil pressure decreases steadily over time and there is a heavy black sludge on the element.

In some high-temperature applications, oil can oxidize and form gums and resins that plug filters. High temperature also can interfere with the action of dispersants allowing contaminants to agglomerate on the filter. A reddish brown appearance of the metal parts of the filter indicates either oil oxidation or fuel dilution. In such cases, the odor of the element indicates where the problem lies: temperature-stressed oil has a pungent odor; dilution features a distinctive fuel smell.

"Particulate contaminants entering through a leak near the air filter not only wear out the rings and increase blowby, but they also enter the lubrication system and plug the filter," Rupert says. "Oil analysis picks this up very quickly."

What about the notion that as filters trap particulate contaminants, they become more efficient? According to Deere & Co., this is true up to a certain point. However, as more contaminants wedge into the paper, oil pressure against the paper rises, forcing once-trapped contaminants through the filter's pores and back into circulation.