Quote:
Originally Posted by chetrickerman
It would be interesting to find out the actual efficiency of the OEM filters at 20 microns. Yes a filter may be rated at 20 microns, but that rating may only be at 50%, or 90% efficiency of 20 micron particles.
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You can also ask the question, how fast does a filter clog when the filtersize gets too small?
Whats worse, a clogged filter or a less effective filter? This is of course more about the filter size issu like the link in the TS hints at than filter efficiency, but more on that later in my views below. (I quote you but my post is not solely directed to your post but more to the whole oil filter debate, so not everything written here is not directed personal to your post)
I have difficulty with some of the intial link claims, where they relate particle size in oil to size between piston rings.
As a rule of thumb, the oil is not really an issue for piston rings, as there is an oil scraper ring first. That removes ALL the oil, or so is its function. If that wasnt the case, your engine becomes an oil burner. So oil never reaches the piston rings.
The reason why oil is shot up the piston (underside) is for cooling of the piston and lubrication of the skirt (that tolerance is huge), NOT for lubricating the piston rings. Thats also the reason piston rings are made of very special material (certainly not oil lubricated bearing material).
So the piston ring size tolerance can never be a valid argument for particle size in oil.
Rodbearing, camshaft bearing etc et however CAN.
On those type of bearings, tolerance is usually 25-35µm, so those size particles and above are important
So if a filter removes typical 20µm+ (doesn't even have to be in single pass) thats fine imho. The rest (smaller stuff) is just extra clogging material.
And I say that it doesnt have to be single pass, because an engine also doesnt work that way. Most people dont know this, but lots of oil filter housings (certainly all bmw oil filter housings) have a bypass on the filter.
This is a failsave on a clogged/collapsing filter (a clogged filter would otherwise starve the engine of oil, destroying it in a few miles).
But the filterhousing and its bypass isn't constructed in such a way that the bypass only opens when the filter is clogged! Its open all the time.
My guess is, that this is done to minimize pressure difference on the filter, as that is the main reason a filter can impact on itself, clogging the canals (it doesnt even have to be clogged itself', impacting on itself, even when the filter is 100% clean is enough).
It is constructed in a way of course that a large partion of the oil is sent to the filter and a smaller part goes through the bypass,unless I totally misunderstood the filterhousing as I examined it.
I build my own custom filterhousing (altering one from another car/enginetype) on my z4 to make certain features possible, and in my view that separation between the 2 canals was done based on flow (canal size) rather than pressure (no pressure valve, the only valve present is a one way valve that sits in the filterhousing is there to prevent drainback to the sump as the pressure is kept on the system by another valve, I think in the head, like in that fram video its silicone and integrated in the filter, with bmw its metal and integrated in the oil filter housing).
And, that TS link somehow also gives the impression that other brands dont have filters that filter sub 20µm because they cant make them that way.
I'll let you in on a secret: a normal coffee filter (cost $0,02) is a perfect 5µm single pass filter.
Making a very fine filter is no challenge.
Making the right filter is.
So I'm very sceptical about stuff that deviates from OEM, because of bigger is always better (or here smaller is always better), because it aint.
A company like knecht, who both develops specifically oil filters and makes high end oil filter housings knows what they're doing. (a bmw M oilfilterhousing is made by knecht, in germany, and a normal bmw filterhousing is not as complicated of design and is made in italy by an italian OEM)
So unless a particular type of engine has a real wear problem where the wear problems for sure point to contaminated oil, I wouldnt change the filter capacity spec etc.
As counterreaction tot the above: lots of M engines have a wear problem on conrod bearings
But as its not present in crankbearings or camshaftbearings with the same spec, its not instigated by particle contaminents in the oil. Also the wearpatterns dont point to contamientissues but rather cavitation and such.
What that fram video means by exceeding OEM spec. In what way as that is extremely important.