Most misrepresented paper on the board unfortunately.
Speculation, supposition, and statements of fact made by people who haven't read any more than the SAE Summary...heck, one time it as raised, a poser stated with utter confidence that it was due to the used oil shearing in service and that thinner oil lubricates better...even defended those statements in the absence of reading the paper, and therefore seeing that the oil had thickened markedly, well out of grade (and no to the usual suspects who will try to turn this into me claiming that higher viscosity did it).
The used oils were typically thickened well out of grade. All had crossed over the TAN/TBN crossover well before the 15,000 mile mark....and some had gone onto "hide the wear metals", where metals that were in the oil at 7-8,000 miles had reduced markedly towards the end … sludge ??? a distinct possibility.
The new and used oil samples were then applied to a cam and disk arrangement, run by an electric motor.
Friction and wear were measured.
The used oils established tribofilms much quicker than the new oil, resulting in less friction and wear versus the new oils, which had to undergo "activation" to form the chemical entities that produce the tribofilms...i.e. you don't just go from ZDDP to iron phosphate glasses without going to something else first...The protective soluble Mo compounds break down to MoS2, which is the protective part in the tribofilms...MoDTC isn't the species that is in the films.
So...used oil forms tribofilms more quickly and effectively than new...surprise surprise.
What that DOESN'T say is that extended OCIs produce less wear, or that fresh oil eliminated the already extant tribofilms
