This paper seems to support that introducing an oil with a different formulation to an already formed tribofilm can have an almost instant effect on the already formed tribofilm - seems to be due to the partial removal/stripping of the existing tribofim, then a rebuilding of a new tribofilm (and a corresponding new friction level) depending on the new oil formulation. Formed tribofilms have a stability factor, and seems both mechanical and chemical means can remove them. A tribofilm is constantly being built and removed, and it's important that the build-up rate is higher than the removal rate. This paper specifically discusses ZDDP and MoDTC tribofilm formations, stability and removal. Figures 11 and 14 are interesting.
They didn't get into how an existing tribofilm built-up with long used oil from a fired engine could be effected by introducing new oil - looks like they only used new oils in this tests. There are other studies that show that an existing tribofilm can be partially stripped with the introduction of new oil.
The AW/AF formulation of different motor oils could have an over-all effect on the wear rate in the parts of an engine where boundary and mix lubrication is happening, depending on their level of formulation difference (which seems to be shrinking in today's oils). As we know, both "film thickness" (MOFT from the oil viscosity) and "film strength" (from the oil AF/AW package) are both factors that determine the over-all wear rate. Oil viscosity is the prime wear mitigator, and film strength is the backup when the viscosity can't provide adequate wear protection.
PDF download: https://www.mgexp.com/phile/1/291112/ZDDP_Paper_Leeds.pdf
They didn't get into how an existing tribofilm built-up with long used oil from a fired engine could be effected by introducing new oil - looks like they only used new oils in this tests. There are other studies that show that an existing tribofilm can be partially stripped with the introduction of new oil.
The AW/AF formulation of different motor oils could have an over-all effect on the wear rate in the parts of an engine where boundary and mix lubrication is happening, depending on their level of formulation difference (which seems to be shrinking in today's oils). As we know, both "film thickness" (MOFT from the oil viscosity) and "film strength" (from the oil AF/AW package) are both factors that determine the over-all wear rate. Oil viscosity is the prime wear mitigator, and film strength is the backup when the viscosity can't provide adequate wear protection.
PDF download: https://www.mgexp.com/phile/1/291112/ZDDP_Paper_Leeds.pdf
Last edited: