Nice thoughtful post, Clevy.
I'll add this ...
Now, all of this is predicated on a HEALTHY piece of equipment; known trouble-prone engines and total neglect negate this concept. Any product has a viable lifecycle, and seriously over-running that term is not a concept I'm discussing, nor advocate.
We used to be married to the 3mo/3k-mi idea, but most folks can see their way past that. "Normal" for most new vehicle is 7.5k miles and often more with an IOLM.
As already mentioned, equipment runs MUCH cleaner than it used to; there just are not many contaminants in today's engines.
Filter lifecycle really cannot be measured by the odometer; it's no different than oil. A filter has no idea how lont it's been in service. The whole concept of one FCI every other OCI would not accuratly predict a lifespan. What if the OCI was 3k miles? Are we to assume the filter is spent by 6k miles? Consider how that would contrast to a person that did his OCI every 7.5k miles; the filter would easily go 15k miles! So, I'm to conclude that the first filter is used up at 6k miles, but the second filter is OK for 2.5x that duration? How can we say that two filters, of identical construction, can have such different lifespans?
So many folks want to OCI and FCI because they perceive it to be "better" for their equipment. And yet, here in the filter forum, we often hear about "failed" filters (often times proof is lacking, but that does not stop the rumor mill in the least). So, if you FCI often, you actually INCREASE the likelihood of inducing filter failure by changing to an unknown entity. Every "new" filter is a "new" opportunity for failure, whereas a filter that has otherwise performed adequately is a proven entity.
Here's the thing about ALL of this OCI and FCI stuff ...
OEMs predicate their recommendations on a two things:
1) covering their booty for warranty costs (an inferred statement of reliablility)
2) other stuff a distant second (environmental friendliness, customer concerns, etc)
As long as condition 1 is covered, then they can concentrate on condition 2. But they will NEVER focus on condition 2, before condition 1 is assured put to bed. No company will stay in business long by worrying about your landfill, if they are risking engine failure costs. You see, if you are actually risking high warranty costs, that means you've engineered and/or manufactured a product that is not reliable. Where is the value in doing such, just to clean a landfill? It does not make sense, UNLESS, you have assured a low warranty risk, and can therefore ALSO reduce waste.
I admire Honda (and others like Mitsubishi) for the 2x FCI. Everything I've ever seen in a HEALTHY piece of equipment says it's doable, and very safe. Why do they reccommend such practice? Because it's safe and conscionable, in that order.
If you have a filter that is not leaking, filtering well, and giving no problems, why introduce the risk (admittedly however remote) of a potential failure of the unknown, when the known is performing properly? While many see an upside to a "new" fitler, I don't see it as such. At best, it's a wash, and probably not even that in reality.
Let's put it in a pro/con perspective ...
FCI with every OCI:
pro - "new" filter ... the anal-retentive BITOGer sleeps well
con - "new" filter increases risk of new individual failure, plus decreases filtration efficiency of lube system, plus increases maintenance costs, plus increases disposal concerns
FCI every other OCI:
pro - "used" filter is a known positive operator because if it's working right then it's likely to continue to work right; saves operating costs; reduces disposal concerns; increases system filter efficiency
con - makes anal-retentive BITOGers lose sleep.
The PROOF (real data and analytical processing) shows filter extension is very viable, despite what your gut tells you. This is the undeniable concern that most folks think "new" is always "better", regardless of the truth of factual basis.
This runs akin conceptually to the frequent OCI mentality. Folks OCI often because they believe it's "better", although it's proven that wear rates go up with this practice. And the alternative of longer OCIs is proven to IMPROVE wear rates. Same goes for filters; they filter more efficiently when used for longer periods, and changing them often does not increase any performance factor at all. Doing these things frequently is admittedly low risk, but there is risk, none-the-less. The alternative is to leave them alone for a safe period of time, and glean the savings while reducing disposal issues. Lubes get better with age, so do filters. Changing them frequently only increases risk of adding in a "new" failure point. To be sure, you could use any product too long, but I don't see that as a big risk to any wrench-happy BITOGers. In healthy modern equipment, OCI and FCIs could easily go 15k miles. The risk isn't to the equipment; that's proven. The risk exists in AR BITOG sanity.
In short, the frequent O/FCI may help one sleep better, but they are proven to be counter-productive in terms of performance, efficiency, and savings. The risk they pose, however remote, does exist, and there is no real, tanigible reward. And no amount of "yabuts" is going to change those facts.
