From the Pennzoil Q&A:
If molybdenum disulfide was good then every motor oil manufacturer would use it in their formulations, however, none do. I won't be so presumptuous to think that I know better than they do.
Fair enough and I respect your view.
I don't make motor oil but do Lubrication Engineering so I will "clarify" their statement. (I chose that word carefully because they are not "wrong" in the sense of error but they are "misleading" in what it leaves the reader to believe)
This is somewhat of an abstract illustrative description for the average reader to easily relate to so a little technical accuracy is sacrificed but not much.
This is why they call it a high stress, high pressure lubricant.
You gotta follow the train for it to make sense.
MoS2 is a solid ( like a crystal platelet or shingle for a visual) and a very small one.
It is a lubricant in the sense that it changes a COF so by its structure its a "dry" lubricant ( albeit suspended in a chemical medium)
It changes the COF by surface reaction mainly within itself ( sliding against itself not unlike ice on ice when augmented with oil)
It bonds to the substrate by a dual action of chemical bonding then "working in". ( think similar to drywall mudding for a mental image) so it leaves a top coat.
"Mechanically" it fills in and smooths surface asperities locally and dips/voids over the run of flatness. ( think finishing concrete for a mental image)
It has limits and liabilities, which some of them are....
Its ability to fill in and smooth is limited by its own structure and compaction coefficient ( being hard and strong- there's a limit to how much it will compact before it breaks off)
It "can" be stronger than the substrate material which the lower stress movement can make it fatigue and flake off under loading then it wants to cut like a carbide impregnated tool. ( wants to chunk out)
It also may not be able to completely fill an asperity ( ceramics can be made much finer) or be able to make the "grade" whole again ( still have some humps and dips in the driveway after scraping)
So for a "motor oil" ( designed for an ICE)- MoS2 has a limited benefit coming out of the gate because in the true EHD regime where the film strength behaves like a true solid- it contributes nothing.
The remaining benefit is the boundary lubrication requirements in the cylinders, rings etc.
The level of that "benefit" will depend on the size and concentration of the MoS2 by volume versus the mechanical conditions it has to deal with in that specific engine ( surface finish, any clearances/tolerances, existing wear and everything else)
So, with the exact same formula and volume- you could put it in 10 different engines with 10 different driving patterns and result in 20 different benefit levels ranging from virtually none to significant.
People who blend engine oils know this so there is no secret here ( they taught me too) and that's why you see it mainly as a specialty additive rather than a standard ingredient because of the following.
A properly designed engine with a proper lubricant maintained properly will see little to no measurable benefit over the life (in general)
An engine subject to extremes in operation or has a degree of wear
COULD ( depends on the extent) see significant benefit.
The biggest benefit of MoS2 is in gearing, grinding, extreme heavy loading ( slow RPM) and ways where its properties are fully exploited.
Hope that helps
Best bang for the buck, as you say.
