dnewton3
Staff member
Gary - as always, you are the ying to my yang!
I guess the only point I was trying to make regarding the comment about start up wear is that this is attributed to the propensity of an abrasive particle to be trapped on a bearing journal, and gouging upon initial motion.
I understand that the bypass filter will slowly remove very small particles from the system, and the engine will also try to replace them.
Quick statement you'd likely agree with, for clarity. At rest, a bearing that might have .002" clearance, will have all .002" at the "top" of the journal, because gravity is pulling the component downward, and there is no oil barrier to separate the journal from the bearing. Once the engine starts and pressure is supplied to the bearing/journal, then hydrodynamic wedge is created and the journal "floats" on the oil layers. It's never exactly split evenly. In fact, it can't be, because of the cyclic motion of the linear portions of common piston driven motion. The journals (crank, rod, wrist pin) actually see their clearance "squish" back and forth with every direction change, in the oil layers from top to bottom; this is ever increasing with the force of the event. As rpm goes up, the forces grow. On the plus side, as the rpm goes up, so does oil pressure, helping to keep the hydrodynamic wedge in place. Agreed?
My point was this: when running, there is very little particulate wear occurring in an engine. The fluid barrier is what keeps things in check. Small particles stay in suspension, harmlessly passing through the system. Only after they grow in size, do the filtration systems catch what they can. That is why surface tension and laminar fluid boundary layers are so important. Oil has to cling to the surface of the metal, and yet slip along itself in ever increasing velocities. At the outer edges of the layers, the velocity is zero when the oil truly is bound to the metal by surface tension. As the layers move inward, they increase in speed, and decrease in tension. This relationship is varied somewhat when abrupt changes in direction occur (think of a river winding along, and it's current near the back versus midstream, near a bend; the "centerline" of flow will rarely ever be in the true "center" of the pathway).
At start up, the boundary layers are not there. It's just the anti-frictional properties of the lube and add-pack that can protect the engine until the pressure comes up. The "slipperyness" of the oil is the most important thing at this point. So, if there is a particle trapped in a bearing journal upon startup, it will have a high propensity to grind along until the boundary layers develop from pressure generation, and the engine components separate from each other. Bypass filtration cannot stop wear at start up, because it has not yet removed the particle from it's location in the bearing.
In a nutshell, wear occurs at startup because particles are where we don't want them. They grind along until the oil pressure separates the components with protective boundary layers. But once that damage is done (a small gouge in the metal) the oil simply fills in that void, because of the extra surface area it can "cling" to. Once the damage it done, it actually provides an additional holding point for tension tenacity. As long as the gouge is not overtly huge, it matters little because during operation, metal to metal contact is almost non-existent.
Because lubricants and engines are so much better designed and manufactured than they were 30 years ago, the boundary layers are so much better at negating the effects of start up wear.
I would fully admit that at the smallest of microscopic levels, you could see where bypass filtration may show distinct advantages. But your analogy of the floor and ceiling are perfect. The rate at which "normal" engine/lube development is moving exceeds the rate of super-filtration application. Bypass filtration (as far as equipment longevity goes) is just about a moot point.
Bypass filtration is all about cost savings these days, and not about longevity. You can keep nearly any piece of equipment in service forever, just with frequent maintenance, using "conventional" lube and filters.
Geez - think of the 4.6L CV examples above. 400k - 600k miles in taxi operation. Think of the HOURS of operation, even more than the mileage. Literally thousands upon thousands of hours at hot idle, followed by short acceleration bursts. But the upside is a very low ratio of start-up vs. continuous operation. All with bulk oil and fleet filters on "normal" OCIs. And not one bypass filter in sight.
I guess the only point I was trying to make regarding the comment about start up wear is that this is attributed to the propensity of an abrasive particle to be trapped on a bearing journal, and gouging upon initial motion.
I understand that the bypass filter will slowly remove very small particles from the system, and the engine will also try to replace them.
Quick statement you'd likely agree with, for clarity. At rest, a bearing that might have .002" clearance, will have all .002" at the "top" of the journal, because gravity is pulling the component downward, and there is no oil barrier to separate the journal from the bearing. Once the engine starts and pressure is supplied to the bearing/journal, then hydrodynamic wedge is created and the journal "floats" on the oil layers. It's never exactly split evenly. In fact, it can't be, because of the cyclic motion of the linear portions of common piston driven motion. The journals (crank, rod, wrist pin) actually see their clearance "squish" back and forth with every direction change, in the oil layers from top to bottom; this is ever increasing with the force of the event. As rpm goes up, the forces grow. On the plus side, as the rpm goes up, so does oil pressure, helping to keep the hydrodynamic wedge in place. Agreed?
My point was this: when running, there is very little particulate wear occurring in an engine. The fluid barrier is what keeps things in check. Small particles stay in suspension, harmlessly passing through the system. Only after they grow in size, do the filtration systems catch what they can. That is why surface tension and laminar fluid boundary layers are so important. Oil has to cling to the surface of the metal, and yet slip along itself in ever increasing velocities. At the outer edges of the layers, the velocity is zero when the oil truly is bound to the metal by surface tension. As the layers move inward, they increase in speed, and decrease in tension. This relationship is varied somewhat when abrupt changes in direction occur (think of a river winding along, and it's current near the back versus midstream, near a bend; the "centerline" of flow will rarely ever be in the true "center" of the pathway).
At start up, the boundary layers are not there. It's just the anti-frictional properties of the lube and add-pack that can protect the engine until the pressure comes up. The "slipperyness" of the oil is the most important thing at this point. So, if there is a particle trapped in a bearing journal upon startup, it will have a high propensity to grind along until the boundary layers develop from pressure generation, and the engine components separate from each other. Bypass filtration cannot stop wear at start up, because it has not yet removed the particle from it's location in the bearing.
In a nutshell, wear occurs at startup because particles are where we don't want them. They grind along until the oil pressure separates the components with protective boundary layers. But once that damage is done (a small gouge in the metal) the oil simply fills in that void, because of the extra surface area it can "cling" to. Once the damage it done, it actually provides an additional holding point for tension tenacity. As long as the gouge is not overtly huge, it matters little because during operation, metal to metal contact is almost non-existent.
Because lubricants and engines are so much better designed and manufactured than they were 30 years ago, the boundary layers are so much better at negating the effects of start up wear.
I would fully admit that at the smallest of microscopic levels, you could see where bypass filtration may show distinct advantages. But your analogy of the floor and ceiling are perfect. The rate at which "normal" engine/lube development is moving exceeds the rate of super-filtration application. Bypass filtration (as far as equipment longevity goes) is just about a moot point.
Bypass filtration is all about cost savings these days, and not about longevity. You can keep nearly any piece of equipment in service forever, just with frequent maintenance, using "conventional" lube and filters.
Geez - think of the 4.6L CV examples above. 400k - 600k miles in taxi operation. Think of the HOURS of operation, even more than the mileage. Literally thousands upon thousands of hours at hot idle, followed by short acceleration bursts. But the upside is a very low ratio of start-up vs. continuous operation. All with bulk oil and fleet filters on "normal" OCIs. And not one bypass filter in sight.
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