Originally Posted By: Shannow
That paper keeps getting trotted out as proof of something that the paper never tested nor demonstrated.
They took a bunch of used oils, some of which were utterly shagged, had thickened excessivly and had poor TBN.
Then they use a contacting surface tribometer and measured the establishment of the tribofilms with new and progressively used oil. The used oil formed tribofilms on fresh metal surfaces quicker than fresh.
This is entirely to be expected, as the first part of the laying down of tribofilms involves partial destruction of the ZDDP/Mo into more reactive species...some additive companies put a lot of different elemental "variaties" in so that there are different points of activation.
So the oil with the most already partially reacted species in it produced the best tribofilms the earliest...exactly as expected.
The Used oil, excessively thick, wiht no TBN to speak of was not necessarily the best oil to have in the engine. Extrapolating the limits (surface tribometer) of this study INTO that realm is really stretching the bow a bit (well a lot).
And at OCI, the quote that you have provided assumes that ALL of the tribofilm is removed to fresh metal (not true, never seen anything on that).
As to the thought process...
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4060600/1
Your observations, and subsequent concerns, are misplaced, as we've talked before.
I'll address your contentions by concept.
First, the talk about how "shagged" (used up) these oils are due to the vis thickening and the TBN/TAN crossover. As I pointed out in other posts, these are essentially meaningless. You keep bringing them up as if they have merit, but they do not. I'll yet again quote the SAE study referenced:
"
It is interesting to note the viscosity of the 7500 mile drain oil is about 20% higher (at 100c) than that of the 3000 mile drain oil and therefore, might be expected to show a lower wear rate because of increased oil film and the resulting reduction in asperity contact. But both oils showed similar wear rates indicating that the wear rate is controlled more by the chemistry of the surface film at the contact than asperity contacts."
You see, despite the thickening and TAN rise, the wear rates did not change;; they stayed essentially the same. Hence, you cannot claim that these two issues (vis and acid) have any merit if they had no effect on the outcome. If there is no correlation (if one characteristic changes, but another does not) then you CANNOT claim there is causation (something affected another attribute). No change in the wear rates means that vis and acid had no affect despite their presence. How you cannot understand this is beyond me; it is CLEARLY explained and denoted in the conclusions of the SAE study.
Also, it is important to understand that the study I reference (2007-01-4133) incorporates information from other SAE studies (which is a very common practice). This study credits info from Fujita et all, which demonstrates that "
the lube-derived film increases steadily with test duration and then stabilizes at the 50-100nm level. This thickness is almost independent of the phosphorous concentration". It went on the show that "
Film thickness is also dependent on oil temperature with higher temperatures tending to promote greater film thickness. However, when a dispersant is added, the film is removed ..." Other studies referenced in 2007-01-4133 speak to the types of ZDDP that have been studied, and how other detergents and dispersants alter the film barrier being discussed. The study further explains that "
They observed that the wear reducing capacility changed with the oil aging and the ZDDP decompsition products gave even better wear reducing capability and lower friction than the ZDDP itself". IOW - the film barrier (TCB) is essentially a byproduct of the ZDDP degradation, but that TCB is actually more important in reducing wear than the ZDDP itself! And it's not just this study (2007-01-4133); it's the culmination of several studies that come to this conclusion. The oils used in the 2007-01-4133 study (which you call a "bunch", but were actually only three) were clearly described in the study. They were:
1) a GF3 with phos at .10%
2) a GF4 with phos at .08%
3) a GF4 with phos at .05%
And yet, despite the difference in phos levels, the wear rate trends were nearly identical. What does this prove? That there is not a direct relationship between phos and wear. While there may be an
INdirect relationship, in that the ZDDP is used as a necessary contributor to TCB, the phos levels in this study, in and of themselves, do not alter the wear rates. What alters the wear rates? OCI duration relative to TCB thickness.
Further, regarding the topic of the SAE study using oils to measure film barriers ...
Yes they took used oil and tested it in some lab rigs; how else would they be able to so accurately track the TBC thickness? So what? If I understand your objection correctly, it's that they used oils with varying amount of accumulated duration (different mileage) and then tested them; obviously showing the "older" oils developed the TBC sooner. I get that, and I don't object to that. But what you seem to want to ignore is that real world data (a huge truckload of data; over 15,000 UOAs) shows similar results. In all my UOA data, folks are not swapping their oils out to alter or manipulate the TCB; they run the oil from fresh-change to some predetermined limit. Some folks OCI often; others run the lubes way out. But the data shows that as the OCI is extended, the wear rates drop to very low rates.
In short,
multiple SAE studies (not just one) have shown how the TCB is established, and how it goes unaffected by other inputs. Further, it is proven that "fresh" oils degrade the TCB, and that heat/oxidation/duration improve the TCB. They show that the ZDDP has less effect on wear rates, than the TCB film it promotes. All these studies are credited in 2007-01-4133; they are listed in the reference section. Are you saying that all these studies are misleading; that none of them prove what is claimed? There are 22 referenced sources; they are all wrong and you're right?
My data echos the conclusions of the multiple SAE studies, but from a different perspective. Whereas the SAE studies take a very scientific perspective, measuring the actual TCB thickness and showing HOW the TCB is developed, my data shows the EFFECTS of that TCB, relative to the OCI duration. The Ford/Conoco study showed in a lab as to how more mature oils develop a thicker barrier. My study showed that real world field trials (15k UOAs) come to the same conclusion. It's the best of both worlds; when SAE studies are backed up by real experiences, it's hard to deny their relevance. It is the combination of the information of the SAE studies, along with the reams of data I have, that leads to a VERY REAL AND LOGICAL CONCLUSION that the TCB, once established, reduces wear to very low levels. And that other inputs (such as vis, acids, etc) don't have a major effect on wear.
You have stated that oil is "shagged" and "completely totaled" because the vis got thicker and the acid flipped. So what? Show me that it matters, sir. What study data do you know of, what can you point towards, that indicates the shift in inputs has any affect on the output (wear rates)? All the information we have available (multiple SAE studies and mounds of UOA data) show that despite the oils experiencing attribute changes (vis shift and acid flip), the wear rates remained steady.
It boils down to this; the SAE studies have shown that the TCB is first removed by fresh detergents/dispersants. After than stripping, heat/time cause the re-formation of the TCB. That TCB will stabilize between 50-100nm of thickness. Once TCB is established, the wear rates go to "near-zero" and become very stable. At some point, it is reasonable to believe that the contamination loading of the sump would overcome this TCB benefit; that particulate would overcome the TCB effect. And while we do not know when that would start, we know from more than 15,000 UOAs that it is AT LEAST past 15k miles, because my data shows this phenomenon with ultra-clear facts. My data shows that wear rates drop around 3k miles, and continue to be very low out to 15k miles. In all manner of engines; gas and diesel, large and small, air and liquid cooled, carb'd and fuel injected, "severe" or not ...
Your objections are noted, and summarily dismissed.