Let me finalize the third in a series of three oil filtration columns by re-viewing terminology used to determine oil filter performance.
The word “absolute” is often used to describe the minimum particle size a filter will remove. This term is meaningless, because, as Paul Bandoly of Wix said earlier, filters are more than just strainers. Small particles can contact the filter media and be captured there (interception), and very small particles can move randomly (Brownian motion) and contact the filter media. The question is “What percentage of small particles will the filter capture?” Besides, if the full-flow filter is too fine, it will plug during the oil change interval, and even a poor oil filter is better than no oil filter.
The Society of Automotive Engineers (SAE) has a series of International Organization for Standardization (ISO) tests for filters that evaluate diesel oil filters with low dispersant oils in a steady-state test. However, this information is only useful when manufacturing filters. OEM filter tests tend to be “special” tests related to a particular engine design.
Keith Bechtum of Donaldson Co. said that in addition to filter “micron ratings” based on laboratory tests, he often sees people use a “mean flow rate” to describe the average size of particles downstream of a filter in a steady-state test. None of these terms describes measurements that are valid in your operation.
Bandoly and Bechtum both agree that the most accurate way to compare filter performance is to compare Beta ratings. You will see results expressed either as a direct Beta rating or Beta ratio. Either expression describes oil filter performance adequately. Beta is a number used to rate a filter’s ability to filter a given particle size (e.g., 2 microns), and it’s easy to convert to efficiency. Just take the beta number and subtract 1. Then divide by the original beta number. So a beta of 2 has an efficiency of
(2-1)/2 = 50% for the particle size in question. Be sure that test conditions are the same when comparing two different brands.
None of these filter ratings addresses engine oil degradation in service. Harmful particles can be removed, but filters cannot remove oxidized oil or oil with insufficient basicity to combat corrosive combustion acids. Detergents and oxidation inhibitors in the oil deplete over time, and dispersants get “tied up” by being attached to soot particles to prevent agglomeration. To combat this degradation one must change the oil, add new oil, or replenish those chemicals (detergents, dispersants, and oxidation inhibitors) that have either been depleted or tied up.
Scientists have tried since the 1960s to retore chemicals to the engine oil to extend its service life. No one was able get the right chemicals to release slowly into the oil. Some marketers simply added the wrong chemicals to filters and let them immediately dump into the oil.
In field tests, one OEM’s trucks went over 100,000 miles without changing oil simply by adding pint containers with the proper chemicals to the sump every 25,000 miles. The concept was valid, but the technology did not then exist to release the proper chemicals into the oil automatically.
One additive manufacturer developed a way to accomplish this by placing a gel of the proper additives into a specially designed container in a Donaldson-developed filter. The results were very satisfying. Oil change intervals were at least doubled in every vehicle in over 20 million miles of testing. Several larger fleets adapted these filters successfully. Unfortunately, oil marketers are unhappy with this concept. Oil marketers typically purchase oil additives and add them to their base oils. Since they are really in the business of moving base oils, longer oil drains diminish their revenues. They have fought this concept since it became commercially available.
