Purifuing your oil

| July 01, 2009

Many bypass oil filter manufacturers claim their products can extend oil life almost indefinitely by removing the finest particles. But major oil refiners recommend regular changes to replace additives such as detergents, total base number additives and exotic anti-wear chemicals that wear out. Consequently, the choice to install a bypass filter can be complicated.

What they are
While the main full-flow oil filter deals with heavy contaminants, a bypass filter “works at a much slower velocity of fluid flow, so it can catch much smaller contaminants,” says Paul Bandoly, technical services manager at Wix. “This maintains a cleaner sump.”

Bypass filters “draw approximately 3 to 10 percent of the oil pump’s capacity at any one time,” says Brent Birch, laboratory manager with Champion Laboratories, but the filter “is designed to clean the oil more thoroughly than the engine’s primary filter. The most damaging contamination particles are in the smaller 5 to 15 micron range. Particles in this smaller range get wedged between moving engine parts, resulting in engine wear.” The standard full-flow filter, he says, is designed to trap particles ranging in size from 15 to 40 microns.

Flow rates may be two gallons a minute, Birch says, though they can be much slower. Oil Purification Systems’ product processes about two to three gallons per hour, says Tom Bock, director of technical sales.

There are two types of bypass filtration systems. The “combination” type filters, which incorporate a bypass section in the same cartridge with a full-flow filter, have an advantage, says Gary Spires of Cummins Filtration. “Cummins’ larger engines use a combination bypass and full-flow filter,” he says, where the design “pulls oil through the stacked discs of the bypass section, so you don’t lose the flow to the oil pan, which represents lost power.”

Other manufacturers, including Wix and LuberFiner, offer filters that incorporate a similar basic design, though different from the patented Cummins system, which ensures that a constant proportion of the oil flow goes through the bypass section.

The more traditional bypass filter is mounted externally, takes a percentage of the flow headed for the engine’s internal parts out of an oil gallery, and returns the filtered oil to the pan. Bandoly says that most engine oil pumps are designed to provide plenty of oil to the engine even if a small percentage is bypassed. Check with your engine manufacturer if you’re in doubt about an adequate oil supply for the engine after installing a bypass filter.

What they accomplish
The highly respected Technology and Maintenance Council of the American Trucking Associations, in proposed Recommended Practice 359 (T), endorses the widely held view that bypass filtration can extend oil change intervals. What’s less certain is just how long oil filtered down to tiny micron levels can be safely left in the engine.

Spires sees extended component life as the main benefit of the combination full-flow and bypass filter that his company, when it was Fleetguard, introduced with the first versions of the Cummins ISX. “A bypass filter removes organic sludge products,” he says. “These are soot tied up with spent additives, a substance that is highly abrasive.”

Bypass filtration can help the big, hardworking parts with relatively wide clearances – the crankshaft and associated bearings, pistons, liners – last longer, Spires says. You’re likely, also, to “save the camshaft and followers and drive gears when you would normally replace them,” whether bypass filtration leads to extended oil change intervals or not.

Birch, whose Champion Labs company developed the first mass-marketed LuberFiner bypass oil filter, takes a less conservative view: “Extending the oil change interval is a function of both cleaner oil and the control of soot that can change the chemical makeup of the oil.”

Bandoly says detergents in high-quality oil keep soot in suspension, and then a bypass filter can remove much of that suspended soot. But if additives work largely to suspend soot, they can lose their effectiveness doing other things, including protecting the engine from acids. “If the bypass filter gets clogged, TAN, or Total Acid Number, increases,” he says.

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