Today’s heavy-duty oil filters have come a long way since the early filters that used wood chips, cornhusks and cotton liners as filtration media. While those materials served the same purpose as the media in modern filters – to trap and hold contaminants picked up by the oil – they were too restrictive to allow all of the oil to flow through. For that reason, only a small portion of the oil could be cleaned at any one time. The rest bypassed the filter and was returned to the sump, hence the name bypass filter. Oil was routinely changed after a few thousand miles.
Those filters served the trucking industry until the early 1950s, when full-flow filters using resin-treated pleated paper media were introduced. Since then filter manufacturers have strived to improve the capacity (ability to hold contaminants) and efficiency (ability to remove smaller particles) while minimizing filter restriction. Bypass filters are used today as secondary filters, pulling in only about 10 percent of the oil, then passing it through to the sump. Full-flow filters are primary filters through which all the oil flows.
Full-flow filters typically trap particles in the 25-to-40 micron range. Bypass filters use finer media and remove smaller particles missed by full-flow filters. They keep oil cleaner longer, extending its service life and enabling longer drain intervals. Dual-flow filters that combine full-flow and bypass filtration are also available. Many lubrication experts feel that both primary and bypass filters are needed to prolong engine life.
Filters should be changed at every oil drain to avoid becoming plugged or clogged so badly that they become ineffective. Full-flow filters have a bypass valve serving as a pressure-relief, opening when the filter becomes plugged. In that situation, unfiltered oil and debris flow through the engine, resulting in premature wear of engine parts.
Advances in filtration media have enabled the development of extended-service filters. Filter media ranges from inexpensive cellulose (paper) to expensive fiberglass, polyester and other synthetics. Synthetic materials enable filter manufacturers to control the precise size and shape of fibers in the filter to catch smaller particles, improving its efficiency and capacity. Some operators like to change oil filters at the engine manufacturer’s recommendation for normal oil service, even for engines operating on an extended drain schedule.
Baldwin BD103 oil filter features cellulose/synthetic-blend media and a dual-flow design that combines full-flow and bypass elements.
Paper or Synthetic Media?
Oil filters trap particles of soot, debris, wear metals and fuel in the pores of the media as the oil flows through the filter. As the pores fill up, the efficiency of the filter is degraded. A decrease in oil pressure, either suddenly or over time, generally indicates a plugged filter.
