First- Thanks to Zebulon for initiating this topic by sharing his findings when cleaning the oil pickup screen.
Second= Once you start reading this you're going to want to say BORING !! Kawboy's off on a tangent again @#$#$ But unless you're an engineer you will gain some benefit from this fundemental understanding of the oil filtration system.
Predictive Maintenanceby definition -Predictive maintenance (PdM) techniques are designed to help determine the condition of in-service equipment in order to predict when maintenance should be performed. This approach promises cost savings over routine or time-based preventive maintenance, because tasks are performed only when warranted.
So how do we analize the oil system to help predict what corrective maintenance needs to be performed or what preventitive maintenance needs to be performed on what frequency.
First we need to understand the design of the oil system. Oil is held in the oil sump. The size of that sump is based on a number of factors which include, heat developed by the equipment being lubricated, in our case the engine and transmission or the gear case in the rear end and the ability to maintain that oil in a temperature range between 220 deg. F. and the breakdown temperature od the oil being used which can be as high as 400 deg. F. The larger the sump, the longer it takes to get the oil up to temperature, Ideally, we want the oil up to operating temperature as quickly as possible and never to exceed the maximum operating temperature. Why a minimum of 220F ? Humidity in the atmosphere can and will condensate in the crankcase and form water droplets. By getting the oil up to 220F will boil off the water and the water vapor will be pushed out of the crankcase through crankcase ventilation keeping the oil moisture free. Also, the viscosity modifiers in the oil are designed to keep the oil for whatever system the oil is in in the proper range for lubricating the moving parts. The quicker the oil gets up to temp, the better the lubrication.
Next in the system is the oil pick up screen. This screen can be 60 mesh, 80 mesh, or 100 mesh and it's sole purpose is to "filter out" particles that can do irrepairable damage to the oil pump. 60 mesh will filter out particles bigger than 250 microns, 80 mesh will filter out particles bigger than 177 microns and 100 mesh will filter out particles bigger than 149 microns. By design, engineers will specify the requirements for the screen based on expected engine wear particle sizes and what the oil pump should be able to manage without catastrophic damage. By experience, usually what one will find stuck in that screen is a result of poor maintenance related activity or a total breakdown of engine components including seal failures. Often upon examination of the screen things like pieces of paper towel or fibers from cleaning cloths or pieces of aluminum foil from the seal on oil containers and such will be found trapped by the screen. Inspection/cleaning of that screen is a sound predictive tool but what's found on that screen indicates things happening which never should have happened in a normal running engine or transmission
Next in the system is the oil pump. By design is needs to supply more oil to the lubricating system then the maximum leaks in the system during the expected life of the equipment. In other words, as the equipment wears out and the tolerances get bigger, the lubricating system needs to accomodate the wear. to do this, the oil pump is oversized and a pressure relief valve is incorporated. When the oil pump meets then exceeds the oil flow through the leaks, the oil pressure builds up and the relief valve opens to releave the excess pressure. For the most part, the oil pressure relief valve is always partially open and it maintains the oil pressure of the system. If your oil pressure is lower than normal one of two things are happening, either the clearances in the engine are way beyond tolerances of a properly running engine or the oil pressure release valve is stuck partially open and not fully closing at lower rpm's.
Next in the system is the oil filter. The oil filter is the only place in the system where you should find normal engine wear debris. By design the oil filter will accomodate the normal debris and filter out particles that could harm the engine parts and have the ability to filter out those parts for a given operating cycle (between oil changes) Usually oil filters are from 15-40 microns by spec. Depending on the requirements set out by the eningeers. For the most part most of the aftermarket filter manufacturers respect the 15-40 micron range. Some manufactures will advertise their products at the lower end of the micron scale telling you their filters are way better than brand XXX. Just remember that the lower micron size (15micron) will flow the best when new and as the engine runs, the filter will start to plug up and the filtering gets better but the flow throught the filter goes down until the oil filter bypass valve opens up I put this in bold because every oil filter has an internal oil bypass valve and you won't find it in the service manual or on an oil system flow sheet. It's an internal protection valve to prevent a blow throuth of the filter membrane allowing all the filtered debris to go through the lubricating system when the filter gets plugged with debris. If you consciously or unconciously don't change your oil/filter on reccommended intervals, you take the chance of running the engine on unfiltered oil if the oil filter bypass valve is open. Not good
A lot of super concious maintenance people firmly believe in cutting open the oil filter and opening up the pleated membrane and look for particles in the filter to help predict maintenance requirements. This is a great thing. you can understand whats wearing by what you find and understand what issues are coming your way. So what you find in the filter media will be anything less than 40 micron.
Last but not least- oil analysis. This is typically not done on automotive vehicles due to the low cost of regular oil / filter changes but is being done on fleet equipment like semi's and heave equipment (excavators, bulldozers etc.) due to higher costs of oil filter changes. a Semi can cost upwards of $800.00 for an oil filter change. By doing oil analysis on a regular interval, oil changes can be extended as high as 500,000 miles but the analysis includes a plethoria of tests. A typical analysis typically costs about $40.00 Canadian. The chenistry of the oil is analized and an oil sample is reviewed under a microscope with a report which will describe the sizes of particles found and type of particles based upon a 50 -100 milliliter sample of oil. Anything found in this analysis should be less than 15 micron. Anything found larger than 15 micron notes a running condition in the engine when the oil filter bypass valve was open indicating excess wear in the engine which plugged the oil filter enough such that the bypass opened.
So lets leave it there for now. Comments ? Questions ?
