Why are bypass filters becoming more common? Because today’s diesels must meet tighter emissions standards, the soot loading of the oil has increased, says Paul Bandoly, manager of technical services and customer training at Wix Filters. Putting the top ring near the top of the piston allows more of the soot deposited on the liner at the end of each combustion cycle to be swept down into the oil pan.
Meanwhile, EGR and retarded timing only make matters worse, Bandoly says. “Bypass gives much better control over soot in the oil, and so it became important as heavy-duty engine oil needed to deal with more soot,” he says. “Some OEMs adopted bypass filters, and the reason they gave for doing this was to control soot.”
Those OEMs include Volvo, which includes a separate bypass filter as standard equipment to facilitate longer change intervals than a standard full-flow setup; and Cummins, whose integral bypass/full-flow filter was introduced with the Signature and ISX. Mack’s MP7 and MP8 engines feature a setup similar to Volvo’s. Caterpillar briefly offered an optional bypass filter on its C12/C13 design, but it’s not available on 2007 and later C13s because of packaging considerations and an increase in sump capacity.
Why is controlling soot so important? One answer is found in SAE paper 2004-01-3014 by Brent Birch of Champion Laboratories, maker of Luberfiner bypass filters. “Soot is chemically active,” Birch writes. “It likely absorbs zinc-based anti-wear additives and competes with these additives for absorptive sites on wear surfaces, contributing an additional component wear factor.” Soot eventually makes the oil abrasive, according to the paper.
The paper’s main focus is a revolutionary type of bypass filter combining a “high-purity, louvered zinc alloy sheet co-pleated with an ultra-high-efficiency, synthetic blend media.” Not only does the synthetic media remove the agglomerated soot once the oil’s additive package no longer can keep it dissolved, the zinc also neutralizes oxidized nitrogen and sulfur compounds in engine lube oil. According to the paper, since the zinc from the filter’s internal sheet is doing the work of neutralizing these acids, the oil’s total base alkalinity (TBN) additives remain stable for a longer time, resulting in lengthier change intervals without compromising the engine. However, the filter’s design has not seen production yet.
A number of other bypass designs on the market claim to allow users to stop changing the engine’s sump oil, or at least greatly extend change intervals. Amsoil, which provides 15W-40 or 20W-50 synthetic oil along with its filter, recommends replacing both the full-flow and 2-micron bypass filters at 20,000 miles and adding two gallons of fresh oil to bring the system back up to capacity, but not changing the sump, says company dealer Jim Flescher.
Clean Technics International recommends a 90,000-mile change for its large filter, and full flows in over-the-road applications, says Richie Russell, the company’s chief financial officer. Clean Technics’ filter is capable of holding 20 pounds of solids and two gallons of water, Russell says. Users should change the full-flow filters at the same time, and add two gallons of oil, again without sump changes until necessary, sometimes as long as 360,000 miles, he says.
Most of Puradyn’s customers change their filters and add fresh makeup oil at 30,000 miles, but do not change the sump, says Kevin Kroger, the company’s president and chief operating officer.
Oil Purification Systems filters are changed at the normal interval for the engine, and necessary makeup oil added at that time, says Bill Preist, the company’s vice president of engineering. Oil changes continue at a multiple of the normal interval and may be extended for as much as 200,000 miles, Preist says.
Cummins Filtration, which markets the Fleetguard brand, does not view bypass filtration as a way to increase change intervals, but as a way to increase engine protection. “Our bypass technology is designed to remove organic sludge compounds from engine oil,” says Gary Spires, senior field service engineer. “These undesirable aspects of lube oil are responsible for major component wear. Removing them by bypass methods results in reduced cost of overhauls when major engine parts are not worn to the point of replacement at time of rebuild.”