Originally Posted by Dave Donaldson

Cheers, I spent 10 years in R and D for a automotive parts supplier for fuel air and oil filtration systems. All testing and product development was done in accordance to SAE J 806 b, and JIS criteria.
On my 300 SDL 1987 I noted a 2 stage filter. pleated paper element, and a cotton element. Most paper elements, as per SAE the standard is 20 microns at 8 psi pressure differential across the media,, at this point the by pass kicks in and by passes the filter. My experience shows that as the filter media becomes more contaminated the ability to filter becomes greater, in regards to filtering smaller particles.. Since the 70's paper media has become known as depth type , thicker cross section,, meaning as the fibers swell with exposure to water it becomes tighter in terms of porosity. The same happens but much more in the cotton element. OEM requirements for our products were higher. The holding capacity, micron rating and ability to withstand pressure differential, {to prevent pleat collapsing and media migration } were more stringent.
We used AC fine dust from SAE spec. and it contained 2 to 200 micron particle size ,Millipore analysis was done and efficiency rate was normally in the 5 micron and 95% capture range but only in the last 50 % of the test. 8 to 10 hr test. contaminate feed rate of 2 grams per hour . So having babbled way too much,,I have done the following on all my vehicles one filter change every 2 oil changes,, and installed a K 55 partial flow filter cotton element that take 5 psi from oil gallery and returns it to sump,, also serves as oil cooler too . Verified that residual partial size is nominal 5 micron, and based on studies by the aviation industry, 5 micron will pass through bearing clearance with out adverse affects, as for rings to cylinder wear it is mostly a issue of end gap ..materials,, and surface finish. Water acids, and chemical formation and sludge are only cured by frequent oil changes. Cheers Dave D. caveat, applies only to autos not fleet / industrial and or stationary applications