Originally Posted By: philipp10
I'm going to play devils advocate here. How do you know that flow is more important than how well it filters. Let's just assume that an engine is producing very low quantities of particles over a given time.
Wouldn't you then say, I don't need to run the oil thru a filter at a very fast rate and therefore, I might as well tighten up what I am filtering down to a smaller particle. In other words, there is a sweet spot where flow rate AND particle filtering size should be optimum. I doubt any of us here would know where that is at but that seems to be the crux of this debate.
The filter designer doesn't want to make the filter so restrictive that the oil pump has to operate near max pressure relief, and/or have the filter go into bypass when it isn't even close to be loaded up with debris.
Amsoil had a situation where their EaO13 filter was designed to run a long 25,000 mile change interval. But if these (or any for that matter) filters are ran that long on a dirty engine they could clog all the way up and apparently effect the oil flow. Could be those filters didn't have an adequately sized bypass valve because it was probably all going through the bypass valve of the filter at that point. Amsoil's fix was to recommend a different filter (one less efficient) or cut back on the filter change interval.
Amsoil TSB (Link)
Yes, the "sweet spot" is to design a filter that provides high efficiency (IMO, 95% @ 20 microns or better), while producing a small delta-p across the filter at high engine RPM and has a high holding capacity to keep well away from the bypass valve opening pressure.
Those filters exist ... normally full synthetic media filters, and that's whey they have been invented; to obtain all of those parameters in one filter.