My next series of columns will focus on selecting lube oil filters based on a better understanding of what is and is not possible with current lube oil filtration technology.
To fully understand lubricants, you need to have a basic understanding of lube oil filtration. To help educate, I’ve enlisted the aid of some people very familiar with development of current filtration systems. Donaldson Co. Inc.’s Keith Bechtum, product specialist, and Brian Tucker, product manager, both provided background –– along with Paul Bandoly, manager technical service, Wix Filter Corp. –– to help me address this issue.
Keith Bechtum made an interesting comment about how filtration systems are currently developed. He said look at filtration design as a three-legged stool, where the legs are efficiency, life (or capacity), and cost. Given the size limitations dictated by the OEM, the filter manufacturer has to balance providing the user with adequate efficiency, sufficient capacity to last the target oil change interval without plugging, and yet be cost competitive. This was easier to accomplish when oil drain intervals were relatively short, but it gets more difficult every day, and it is currently driving an evolution in oil filter technology.
Before discussing the latest filtration developments, let’s review the basics (the physicist in me is coming out). Most people think that filtration is equivalent to straining the particles out of the oil, but it’s much more complicated than that!
Paul Bandoly said that liquids are filtered by straining (the particle is larger than the opening), interception (the particle hits the filter media and is captured there), centrifugation (the heavier-than-oil particle is slung to the outside wall of the container), and diffusion of very small particles due to something physicists call Brownian motion. The trick is to know how much oil filtration is required. Glacier Metals did a landmark study in the ’70s, which showed that most bearing wear was caused by particles in the 5-to-15-micron size range. Larger particles were easily filtered, and smaller particles simply went through the system without doing any damage.
Today the results of this study may no longer be totally applicable. Close tolerances in fuel injector and valve train components would be expected to require finer filtration. Extreme pressures in injectors and valve trains, and the lack of new lubricant flooding of critical valve train areas, can also be factors. Modern diesel engine oils are also much more difficult to filter.
So what is required to provide adequate oil filtration? Consensus has it that the oil should be filtered as finely as possible without the filter plugging before the end of the scheduled oil change interval. Remember, when the oil filter goes into bypass mode due to an excessive pressure drop across the filter, no oil is being filtered. You could bring the vehicle in to change the oil filter, but that would involve considerable cost and reevaluation of your original maintenance scheduling.
Years ago, bypass filtration (actually a misnomer) was developed to allow finer filtration of lube oil particles. This finer filtration was accomplished by diverting some of the lube oil stream (usually 10%) through a huge depth-type or centrifugal filter. The lower oil-flow rate gave these filters additional time to remove harmful particles from the oil.
Of course, incorporation of such secondary or supplemental filtration involves considerable parts and labor expenditure, so the fleet operator needs to be certain the additional expense is justified. Some of the claims made by aftermarket supplemental filter manufacturers may have everyone confused. In the next couple of columns I’ll discuss how to compare oil filter claims to help fleet managers make more intelligent purchase decisions.
