Bypass filters like this Gulf Coast Filters model are useful in extending oil change intervals. Because engine oil is kept clean, monthly oil drains can be extended to as few as one or two a year. That can save four to 10 trips to the shop and several hundred dollars of oil and primary filters annually. Bypass filters cost $400 to $600 and less than $50 per replacement element. They install in less than an hour. Payback is from one to two years. Photo: Jerry Sims/Gulf Coast Filters

By Paul Abelson

Oil changes take vehicles out of service for anywhere from several hours to a full work day. To extend intervals, many fleet managers use bypass filters (more on these later). But operators still have to bring in their vehicles at specified mileages for “dry” preventive maintenance, such as chassis lubrication.

Automatic chassis lubrication

The virtually continuous flow of grease provided by on-board lubrication systems, however, enable preventive maintenance to be scheduled according to oil analysis results instead of mileage.

Traditional — or zerk — lubrication fittings are permanently installed at grease points so technicians can attach grease guns and add grease manually. Automatic greasers consist of a central reservoir, a pressure pump, a manifold to accumulate and distribute grease to hoses, and special fittings that replace the zerk fittings. The systems:

1. Deliver optimal quantities at preset intervals. This eliminates both over-greasing, an environmental and safety hazard, and under-greasing that leaves bearings and wear points unprotected.
2. Distribute grease evenly and completely to all fittings, eliminating the possibility that a technician will inadvertently skip one.
3. Are sealed, so they can't be contaminated.
4. Reduce material costs by up to 25% by reducing waste.

Ultrafine filtration

To lengthen the time between changes, the engine's oil must be kept clean. The best way to do this is with bypass filtration.

The term “bypass” describes how the process works. After all the oil goes through the full-flow (primary) filter, a small amount of oil bypasses the engine to go through the bypass (secondary) filter, and returns to the oil sump. The process removes particles smaller than 3 microns (a micron is one-millionth of a meter, or 0.000039 inch) compared to 25 microns with the best full-flow filters.

To keep from blocking this ultrafine system, only 3 to 5% of oil is filtered during each pass through the bypass filter. Engines pump 40 to 70 gallons of oil a minute, so although flow per pass is small, virtually all the oil passes through the bypass filter every few minutes. Once cleaned, it stays clean.

How to optimize automatic lubrication
  • Make sure the system's reservoir doesn't run out of grease. Just as engines suffer bearing damage and risk seizing up if oil is contaminated or low, inadequate or contaminated lube threatens bearings, suspension, steering, and driveline.
  • In one component survey conducted by TMC, inadequate lubrication accounted for 34.4% of chassis failures and contaminated grease accounted for 19.6%.
  • On-board lubrication systems can be specified along with other truck components or purchased later from your dealer and installed by the dealer or your own technicians.
  • If weight or cost is critical, an alternative is a centralized lubrication system with a central block manifold, hoses, and fittings leading to as many as 12 points per block. If you grease one point, the grease will go to every fitting. You control how much grease is used.
  • If you're going to add an automatic or centralized system, you might want to wait a few months because there may be warranty issues. Meanwhile, have your new truck serviced at a dealer — again, in case there are warranty issues.

Instead of the single layer of media found in most primary filters, bypass filters use depth of material to accomplish their task. Some are made with tightly compressed fibrous waste such as shredded paper, cotton remnants, or sawdust. But vibration opens channels in compressed materials, especially when they're wet with oil, enabling larger particles to migrate through the filter.

The most effective bypass filters use highly tensioned rolls of filter paper instead. They're quite dense and present a great deal of depth for multiple layers of filtering, allowing them to remove even submicron particles.

By using bypass filters and automatic greasers, some fleets have doubled and even tripled the time between preventive maintenance intervals. To determine optimal drain intervals, oil analysis should be done at regular intervals, with results charted to project trends.

— Abelson ( is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.


For a list of automatic lubrication system and bypass filter suppliers, click here.

Is a 360-degree view on the horizon?
Fleet columnist Paul Abelson envisions the next step in onboard technology.

Even the most aerodynamic mirrors disrupt air flow, raising fuel consumption in heavy trucks by more than 5%, and don't cover all blind spots.

Tiny TV cameras, on the other hand, can be enhanced using infrared and low-light technologies to perform better than mirrors. Vision systems employing a camera and dash-mounted screen virtually eliminate aerodynamic drag.

They can also be used to capture images that can be used as evidence if operators are falsely accused of causing crashes.

Other devices, available now, provide lane guidance when coupled with image analysis, reducing the likelihood of incidents that require repairs.

The greatest obstacle to mandating vision systems in light-duty vehicles is the federal government. Motor Vehicle Safety Standard 111 requires trucks to mount external mirrors. Until the standard is amended to require vision systems, no progress related to a driver's range of vision will take place. The motivation to amend the standard may be improved fuel economy.