Allow me to quote myself from a different thread ...
The topic of BP filtration is really no different than most any other topic under the sun. You can either properly or improperly utilize something, and that often depends upon the conditions under which that topic will be applied. Taking something out of context is unlikely to lead to success, and even if one stumbles onto good results, it will be by chance and not due to deliberate act.
BP filters are a fantastic way to greatly extend the OCIs of any piece of equipment, but they are probably THE most understood tool in the toolbox of maintenance choices. Most people will get sucked into the BP filtration concept because they think (in error I'll add) that a BP filter will make for less wear in an engine, but they don't understand what conditions that may or may not be true. For several reasons, BP filters don't have the effect people believe them to, because of the intent of OCI duration.
The vast majority of misinformation regarding BP filters comes from the marketing garbage of most any BP filter maker which touts the infamous GM filter study from decades ago. That study is grossly misunderstood, and while not completely flawed, leads to terribly erroneous conclusions for the uninformed.
The reality is that BP filtration is not significantly effective at reducing wear in any way if a "normal" OCI is your intention. And the main reason this is true is because, while BP filter elements are very efficient at removing particles down to 3-4um with absolute results, the dirty little secret is that soot (the primary cause of wear generated from inside the engine) actually starts out about 100x smaller than that. Soot typically starts out around 40 nm in size, give or take a bit. It is pretty much impossible for a BP filter elements to affect soot-related wear in a normal OCI, because the soot has not yet amalgamated to a size where the filter element will have any efficiency at trapping it. What controls soot at such small sizes is the additive package in the oil; the anti-agglomerates and dispersants are what keep soot from keeping too large. Over the life of the OCI, there is eventually a point where the soot particles will co-join en-mass and then start to be an issue. But there are a massive slew of UOAs which show "normal" OCIs (out to 15k miles) have very desirable wear rates even without using BP filtration. And when UOAs are done in "normal" OCIs which have the claimed benefit of BP filtration, there's never any statistically significant proof that the BP filter element improved anything in terms of wear reduction.
The reason BP filters have the potential to be a good choice is because if you intend to run the OCI long enough, the soot control they offer can be hugely beneficial in really long oil runs. Once the additive package starts to be compromised (past 15k miles as my data indicates), THEN the BP filter element becomes a major player in the wear control, because the soot amalgamation is becoming much more prominent.
And, extended OCIs need to be monitored with UOAs, so that you know what's happening in the sump.
There are some really good examples of how BP filtration can clean up a sump fairly well; that is true. But what's not been shown with any reasonable link to causation is how much those effects truly affect one's vehicle lifespan. Most vehicles made in the last few decades have drive-trains that will outlast both the general decay of the body and also the probability of intended ownership. So why spend money and increase maintenance issues if the "improvement" really doesn't change the overall ownership effect?
Various members over the years have quoted a general concept that rings true; using BP on a typical daily driver is likely to give you the best running engine in the junkyard after your car is totaled in a wreck, or benefit the 4th owner after you traded it off long ago.
Anecdotal stories abound on both sides of this issue. ...
- There are some examples of BP filter systems doing a great job of performing for guys who run really large sumps, really long OCIs and really long ownership terms. For them, BP makes a ton of sense and I applaud the proper use of the tool.
- There are also examples of vehicles going 1M miles without ever seeing syn fluids or premium filter systems. Just good routine maintenance practices. (Search "million mile Chevy truck" or "million mile Ford truck"; they're out there!)
I will never say that BP systems are a great idea or a terrible idea. I will only say that BP systems are a tool that many people misunderstand and often mis-apply. But when used under the correct conditions, and as part of an overall maintenance program (BP, UOAs, PCs, extended OCIs, etc), they certainly can give a good ROI.
The thing to understand is that really long engine life is not a benefit exclusively offered by BP filters. The same effect can be found by doing normal oil changes. Simply put, you can either filter out or flush out the contamination. The end result (long engine life) will be a benefit of either approach. There are two roads to the same destination; filter or flush out contamination. So, BP filters cannot fairly claim an exclusive benefit they don't truly enjoy. They CAN do a good job in right circumstances. Otherwise, they're an unnecessary band-aid that only adds cost and complexity; if that's your thing - if you just like to tinker and don't care if you're wasting money - go for it!
Additionally, intake air filtration is a huge contributor to overall engine wear. I believe it to be as important, if not more so, than oil filtration. But that's a different topic for a different thread ...