Originally Posted By: jimbrewer
"One word of caution; check for sludge. Not that it will happen, but it is always of concern when running longer OCIs. Generally, if the engine is not a known sludger, this is not an issue, and 15k miles is doable here. With insolubles low, and the history of the 2.5L, you should be fine, I suspect."
Non-rhetorical question for Mr. Newton. How does sludge come about when the UOA is so sterling?
More rhetorical. Why push it? the UOA costs as much as the oil change. I accept your proposition that the oil lubricates better and better until it fails, but a guy who is running it out to 9K must be getting a lion's share of that effect. Since sludge is evidently possible notwithstanding excellent numbers as you say, isn't this all the more reason to call it a day at 9K and side-step this possible problem? Besides, isn't there test-to-test variation that has to be taken into account? For example, suppose OP successfully runs his oil to the failure point at 15K. Isn't there a fair possibility that the next failure point might be 12K, just as a matter of test to test variability?
Wouldn't the optimal thing be to change the oil every 9K with exactly the same stuff, quit paying for the UOAs and perhaps devote more time and money to the cosmetics of the vehicle? My experience is that the appearance chases a person out of a well-maintained vehicle more than the mechanicals.
There are predictors such as the insoluble count; when that is good, it's unlikely that sludge/coking is a big issue.
However, I had good UOAs from my old Taurus that had seriously coked rings. I was unaware of it until I did a compression check.
We go with what we know. And the more we know, the better decisions we make.
If the valve cover is easy to pop off for an inspection, why not confirm the low insolubles with an independent visual check?
Nearly every example I have (with the exception of known heavy sludgers) shows wear numbers still dropping out to 15k miles. That does not mean the wear starts to escalate there; it means that is where the data drastically tapers off. Same goes for the Ford/Conoco study; they didn't see wear rise at 15k miles, that is just where they stopped the testing.
I would love to put together a troop of brave soles that are willing to find the fundemental edge of sanity (with a nod towards the necessity of safe equipment operation). I would include myself in that; I am willing to put my money (and vehicles) where my mouth is. Let's run up some 10-15k mile OCIs, and track all the inputs/results we can. In longer OCIs, I see the logic of "better" filters being a possibility, simply due to the much greater holding capacity. (Of course, one could also get that from an upsized filter or twined FF filters.).
Jim - Why push it? For the sake of knowledge. Yes - small sump systems will likely never be able to meet any ROI that includes a UOA, especially a Blackstone with TBN/TAN ($$$). But that is the point I try to make; learn from others! I have MOUNDS of data that shows longer OCIs are safe, and I have personal UOAs that show dinos are way more capable that others are typically willing to admit, or will admit but only begrudgingly. In the face of clear evidence, some just cannot accept the reality. So, they/he/we/she all experiment to see what we can find out, realitve to what is important to us as individuals.
Ironically, if one is seeking the "best" ROI, you have to spend money up front to make it back in the end. I would never suggest folks just blindly run up to 15k miles without a few UOAs for confirmation. To many other potential issues that also need tracked. This is where folks who run synthetics and premium filters falter; they never run out the system long enough to make back the money. And then they often UOA and ignore what it tells them.
Sometimes knowledge is worth the price of admission. I would be the first to admit I often UOA simply out of a sense of curiosity and cannot justify the cost; it's an emotional satisfaction I seek at times. I can be cheaper to OCI than to UOA for sure, at times.
So the question becomes this:
Where does the OP want to take this? What balance does he seek between knowlege and ROI? As to this OP and his UOA, I'd say working up towards 15k miles is certainly doable. Will need a TBN/TAN the next time as only knowning TBN is only half the equation. But that is only if he "wants" to do so. The wear metals are very much in control and low; the contamination is low; the TBN is likely OK but needs a TAN to confirm. Other than a pure gut reaction, give me a good reason he shouldn't extend in the pursuit of happiness? To what characteristic in the UOA would anyone point out that necessitates shorter OCIs? What measurable is near condemnation such that longer OCIs are not doable here? Don't give me your gut emotional reaction; point toward the clear evidence that suggests this isn't pragmatic. Because EVERYTHING I see in this UOA says it's safe to extend, and a TAN would be helpful.