I have performed a lot of oil analysis tests on my Subaru Outback XT and one or two on my Jeep GC through
Blackstone Labs. I tested many of the higher quality synthetics that are generally available, along with Wal-Mart's Tech brand. I did not test Royal Purple or other oils like this not generally available at the local Wal-Mart or general auto parts stores.
The least effective was the Wal-Mart Tech brand, but it was still usable after 3500 miles. The best tested was Mobile One and still had quite a bit of additives left. I tested all at ~ 3500 miles as the Subaru was/is still under warranty and required oil changes at 3,750 miles. I have standardized with Mobile 1, but all had good properties at only 3500 miles of usage.
Some years ago I also standardized on K&N oil filters due to others tests that placed it and Purolator PureOne tied for first place by a significant margin above the many others tested. PureOne is available at local auto parts stores usually for a few dollars less than K&N. And K&N needs to be ordered from Amazon or race parts shops like Jeg's Racing or Summit Racing. I prefer the large nut on the bottom of the K&N for removal of the oil filter with a socket.
Over the years I have also standardized on K&N air filters for all of my vehicles. The oil tests also show the K&N air filters are doing their jobs, even though I only clean them every couple of years. I will try and find one for my Kioti, but do not expect to be successful. Same way with the oil filters
Here is an article I gleaned from elsewhere, maybe a post on TBN. I will standardize on Mobile 1 for my tractor also, due to its tested rating from this article, availability and price vs. the #1 and #2 oils. But in the end, I think it is difficult to purchase a bad oil these day as long as one stays with the major brands.
Diesel Oil