All that matters from that report is that between M1 (sample 7/9/22) vs VR1 (sample 8/3/22) which were very close together: (1) wear metals for similar OCI dropped in half, (2) oil viscosity held up better for VR1. (1) might be because break-in is still happening, though after 8k miles I'm not so sure. Regardless the two UOAs were very close together so I would have expected the influence from break-in still happening to be minimal. However, (2) seems unlikely to be caused by the engine breaking-in. However, as I mentioned after over 8k miles I'd expect the engine to have pretty much broken in, so I'm not quite sure why you say break-in is clearly still happening. These weren't easy miles either, a significant amount were driven on the track in high RPM and high engine stress situation.
Break-in typically takes a lot longer than 8,000 miles, my SRT is still breaking-in, as evidenced by my recent UOA. Our truck is now probably broken-in, as it seems to have settled down to what's pretty normal for that engine.
And that's what used oil analysis is about, finding out what's normal for your equipment, and then tracking for deviations. An engine that is still in the break-in phase will naturally show a trend-down tendency as the miles accrue and eventually, those numbers will settle. Of course the tool is also not supposed to be used to contrast different oils with each other in this manner. It takes hundreds of thousands of miles and hundreds of samples statistically analyzed as
@dnewton3 has posted recently. Though I appreciate tear-down analysis isn't a practical proposition, despite being the correct tool for the job.
We should be careful about drawing conclusions about viscosity without looking at the virgin viscosities. The Mobil oil starts out 2.5cSt thinner than the Valvoline at 18cSt vs 20.5cSt. So, all of these results are in the context of that difference.
An example, if I use a viscosity calculator and put in 18cSt as the starting visc for M1 15W-50 and then put in 1.37% of 0.5cSt fuel, the resultant viscosity is 17. Of course a viscosity calculator doesn't work properly on dissimilar fluids, but it should give an idea here. If I bump that to 2.53% fuel, I get 16.2cSt.
So, deviation from calculated:
1. 1.37% fuel: 4.3% visc loss (17cSt vs 16.3cSt actual)
2. 2.53% fuel: 4.5% visc loss (16.2cSt vs 15.5cSt actual)
Now, let's do it for VR1. I put in 20.5cSt as the starting visc, then put in 2.36% of 0.5cSt fuel, the resultant viscosity is 18.48. I bump that to 1.84% and its 18.9cSt. Bump it to 2.43% and it's 18.42.
deviation from calculated:
1. 2.36% fuel: 10.0% visc loss (18.48cSt vs 16.8cSt actual)
2. 1.84% fuel: 11.8% visc loss (18.9cSt vs 16.9cSt actual)
3. 2.43% fuel: 12.3% visc loss (18.42 vs 16.4cSt actual)
I have a thread on this imperfect method of determining visc loss from fuel dilution here:
Reading back through an older thread that @Gokhan posted today, with his more complex viscosity calculator (the caveat being you need to know alpha for it to be accurate) with the idea of it being more useful for mixing dissimilar fluids I recalled some recent discussions about the impact of...
bobistheoilguy.com
But the takeaway here is that even if the visc loss for fuel isn't perfect, the deviation, applied universally here, still gives us a useful result.
If we add one more set of calculations here:
M1 at 2.53% fuel is a deviation from virgin (18.0cSt vs 15.5cSt) of 16%
VR at 2.43% fuel is a deviation from virgin (20.5cSt vs 16.4cSt) of 25%
So, overall, the Valvoline oil has actually experienced higher viscosity loss than the Mobil. The problem is that the virgin viscosity isn't being taken into consideration when looking at the results.