Originally Posted By: ArcticDriver
This is a great question and I have yet to see an explanation of what makes CK-4 a better product.
I respect the various wear test results but I wish the chemistry would be explained.
I've been giving this some thought since I have been using CK4 RT6 in my Cummins Dodge for about 48000 miles. I had a VOA done on the CK4 and was bemoaning the lower ZDDP content that has apparently dropped from ~1200 to ~1000 ppm. At the same time, TBN has decreased in RT6 from 10.6 to 8.8. Magnesium is almost gone, and Calcium has been increased. I think what is going on with this oil is that even though the antiwear additive has been decreased, so has TBN, by about the same amount (20%). It has long been noted on BITOG that Antiwear and DI additives compete for surfaces within the engine. So by decreasing both the same amount, the additive package remains balanced. High TBN is no longer needed in this era of Ultra-Low Sulfur Diesel, so Shell is taking advantage by lowering DI additives, and then Antiwear in the same proportion. I did a 30,000 mile OCI on my truck earlier this year, and the oil still had usable TBN at the end. Iron wear metal has stayed about at the same as the UOA's with CJ4 RT6 that I did back in the 2013 time frame. I have 18000 miles rolled up on a new fill of CK4 RT6, and will be sending in a sample for analysis in a few days.