Regarding soot, that's a very misunderstood topic.
Soot in most engines starts out around 40nm in size, give or take a bit. That's NANO-meters, not micro-meters (um). Think about it for a second ...
Soot that is 40nm in size has to "grow" (amalgamate, or co-join) with other soot particles and increase to 100x (one hundred times) its initial size, just to become 4um. And as we all know, most particles smaller than 5um really pose little threat in terms of wear. So soot must grow 100x larger just to even approach being a concern.
Most bypass filters (any of the major brands like Amsoil, Frantz, FS2500, etc) really only become truly effective when the particles are around 3-4um and larger; they will be "absolute" in efficiency around that size. So any particle smaller than that will pass right through even the most efficient of bypass filters.
Part of the oil add-pack is the anti-agglomerate; the stuff that keeps soot from amalgamating. As long as the oil is in good shape and not overwhelmed, the additives will keep soot from "growing" larger, or at least significantly slow the progess of growth. Now consider the OCI practices. OCIs flush out the majority of all contamination (admittedly not all, but darn near most of it). Fresh oil with low contamination and a strong add-pack really has little concern for soot. Though there may be a lot of soot near the end of an OCI, that doesn't mean that the soot is large enough to do damage yet. Most of the soot is still too small to make a significant impact in wear rates. If you horribly overran the OCI, and didn't have BP filters, then it would be a major concern. In effect, it's not filtration keeping soot in control in a normal OCI; it's the oil additives. You can have 3% soot by volume, but as long as those particles are small, they mean little and the wear rates are not affected. Never confuse particle quantity with particle size.
BP filters don't make equipment last longer. BP filters make oils last longer in service by keeping them clean over a very long OCI. BP filters haven't been shown to statisically make a difference in wear control in short-to-moderate OCIs. BP filters are a fiscal savings tool in regard to oil changes, not equipment life. Low wear rates are not exclusive to the use of BP filters. You can get low wear rates by just changing the oil frequently enough that you flush out contamination rather than filter it out.
There are countless examples of similar engines run in very similar conditions, which have different filtration systems. Those that use BP filters really have shown zero (none, zip, nada) advantages in terms of wear control in "normal" OCIs (less than 15k miles). There are some old UOAs here on this site for some Dmax diesel engines. Two trucks drove from the midwest, out through the Rockies, pulling RVs. One ran syn oil and BP filtration; the other ran dino oil and a typical FF filter only. And yet, at the end of 6500 miles, both trucks turned in nearly identical UOAs in terms of wear metals. The BP filter did absolutely nothing to improve the wear rates, nor did the syn oil. Why? Because in 6500 miles, the OCI didn't accumulate enough contamination yet to make any burden to either system. The BP and syn fluid cost about 4x more money, and returned not one penny of benefit over the standard filter and oil.
BP filters are a fantastic tool to extend OCIs. They make a lot of sense in large sump systems where the costs can be spread out over very long OCIs, especially when the oil change volume is measured in gallons and not quarts.
But BP filters are not a one-size-fits-all answer which will assure you of success in all applications; that is patently untrue. In short-to-moderate OCI durations, they do pretty much nothing but waste money because they do NOT improve wear rates when contamination levels are low, and the soot is still very, very small.
In this work, an investigation of soot-in-oil samples drawn from the oil sump of a gasoline direct injection (GDI) engine was carried out. Soot partic…
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