Bypass filters are designed to remove smaller particulates than would be removed by an engine's normal filter, so that the need for additional oil or oil changes can be reduced.  High density bypass filtration extends the useful life of oils.  In addition to reducing waste oil generation, collateral benefits include reduced acquisition of petroleum-based lubricants, reduced-labor hours in the management of waste oil, and an extension of engine life through improved lubrication.

Bypass filtration is a system that provides high density, slow filtration (one to six quarts per minute at engine operating temperature) of engine oil without affecting the primary OEM filtration system.  Bypass filters also remove solid contaminants down to 3 microns, control moisture content in oil, are compatible with all MIL-SPEC oils and extend oil drain intervals.  Bypass filters are installed in the engine compartment of a vehicle or, nearby a stationary engine.  The bypass filter is fed a slip stream of oil that bypasses the engine.

Oil added during filter changing, and to replace burned oil, is normally sufficient to replenish the oil's additive package (the component of the oil that is responsible for maintaining pH and preventing deterioration of the oil).

Installing bypass filters may not be feasible on some vehicles in a fleet.  The climate in which the vehicle is sued, the duration of engine run time, and the age of the vehicle can all influence the feasibility of bypass filter use.

In warm climates (where 15W40 is used year round) all vehicles benefit from the additional filtration because flow through the filter starts almost immediately.  However, in colder climates, engines need to run at the manufacturer's normal operating temperature for at least ten minutes to reduce the oil's viscosity and to allow flow through the bypass filter.  Longer run times are necessary in extremely cold climates.

Several different types of bypass filters are available.  Those manufactured by Gulf Coast and Enviro Filtration rely on filter elements that remove particles down to the 1 to 10 micron range.  The Gulf Coast unit is distinctive in that it uses a commonly available roll of toilet paper (or paper towels for larger units) as the filter element.  The TF Purifiner unit filters down to 0.5 to 1.0 micron, and then refines the oil by passing it through a heated element refiner that is vented back into the engine air intake.  The heated element volatilizes any unburned fuel, water, or glycols that contaminate the oil and cause the oil's additive package to breakdown.  These systems reduce the need for complete oil changes, but the engine's conventional canister filter along with the bypass filters still need to be changed in accordance with manufacturer's recommendations.

Along with filter changes, engine oil must be sampled and analyzed to determine the physical and chemical properties of the oil (see data sheet 6-II-3 for Lubricant Analysis Programs).  Using a bypass filter system in conjunction with a lubricant analysis program may reduce the number of oil changes without decreasing the life expectancy of engine parts.  The use of bypass filters has been approved for use in Air Force vehicles.

According to Mr. Mike Schleider, Chief Engineer for the Support Equipment and Vehicle Management Directorate at the Warner Robins Air Logistics Center, the use of oil bypass filters in Air Force vehicles has been approved for use once a base has petitioned their MAJCOM for an exemption from the periodic oil change intervals called out in T.O. 36-1-171.  However, if approved, these filters will be required to be used in conjunction with an oil analysis program.  The oil analysis program is to be used to determine oil change intervals.

• Reduces the number of oil changes required.
• Reduces new oil purchses.
• Reduces the generation of oil waste and the associated costs of waste oil handling and disposal.

• Payback period may be longer than life span of the vehicle.