Separating the oil from the chaff

| August 01, 2001

Advanced filtration is not a new concept, but it’s getting more attention lately for its ability to extend service intervals, and, soon, to provide added protection against the extra contaminants expected in diesel engines built after October 2002.

Despite their potential benefits, the systems are getting mixed reviews because they’re reportedly often used as substitutes for proper maintenance procedures.

Most of the devices and all of the debate involve technology designed to deep-clean oil. These are bypass filters that route a small portion of the oil flow through extremely narrow passages capable of snagging particles as small as a half-micron. Standard filters, by comparison, catch crud in the 12- to 20-micron range.

Proponents of the systems say cleaner oil lasts longer and does a better job of protecting internal parts against wear. Although such claims seem logical and indisputable, some people say they are also exaggerated and misleading.

Jim Pirie, an application engineer at International, says engine makers require all approved filters to meet a certain cleaning standard, and anything beyond that won’t necessarily result in greater component longevity. “It’s just an additional cost without a lot of benefit,” he says.

Pirie also takes exception with the promise of greatly extended drain intervals. “Filter manufacturers have encouraged people to push their [drain] limits out further than any engine guy would like to see,” he says, “even further than the threshold for harming an engine.”

Pirie says contamination isn’t the only reason for changing oil. “Over time, the oil’s additive package gets depleted, and the only way to replenish it is with new oil,” he says. “You can’t just dump in a bunch of chemicals and hope for the best.”

Surprisingly, that’s exactly what some vendors have encouraged truckers to do, says Ross Iwamoto, a research scientist at 76 Lubricants. He says aftermarket additives are not a good way to fortify oil. “You can’t possibly hope to match the original additive chemistry of all the oils on the market,” he says.

Additives serve several functions as antifoam and antiwear agents, corrosion inhibitors, detergents and soot dispersants. Iwamoto says soot will become increasingly troublesome late next year, after engine makers introduce exhaust-gas recirculation to achieve federally mandated emissions standards. He predicts soot levels will double, from 5 percent to 10 percent. Oddly, such a jump would affect additives more than filters.

A lot of soot is smaller than 1 micron, so it easily passes through most filters. Dispersants are designed to keep these little bits from clumping together, creating bigger globs and, ultimately, forming sludge. The latest oils, PC-9, are supposed to be able to handle up to 9 percent soot – if their additive packages are in reasonable condition.

With current engines, Iwamoto says, additive packages will go a considerable distance in line-haul operations as long as premium oils and filters are used and regular analysis is done. “We’ve seen quite a few fleets go to 40,000 or 50,000 miles,” he says. “More typically, though, it’s somewhere in the 25,000 to 30,000 mile range. There are some fleets going 80,000 or 100,000 miles, but those are definitely experimental, using special oils. They’re also trading off a little bit on durability.” He says the industry’s average drain interval is about 22,000 miles.

Iwamoto says there are several good filters on the market. “I think fiberglass might have a little better performance than the traditional paper media,” he says. “The centrifugal products also do a good job. They basically work off the density difference between the soot and oil.”

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