Hey Steve S. hopefully you can keep those wildfires under control out there!! As far as your question is concerned the real issue we face mainly is the TBN starting points vs. the rate of depletion. Granted the rate of depletion is less per 1,000 miles than the CI-4 counterpart (i.e. Delo 400 LE for Delo 400 MG), but the intersection of the curves affords a noticeable difference (approximately 3,000-5,000 miles in my last two studies) in the end point where TAN starts going vertical. The older CI-4+ formulations also seemed to be more tolerant of EG based extended life coolant contamination than the new formulas...viscosities and TBN really move to the dark side quickly when coolant gets to the CJ-4 (I really don't understand this one based on the formulation change, but the data shift was quite noticeable)!
In the absence of coolant contamination wear metal generation (as measured via ppm/1,000 mile per UOA) comparisons afforded no statistically significant difference between CI-4+ and CJ-4 populations (tested at alpha 95% beta 15% for all you stat geeks out there). This held true when comparing paired vehicles from 1999-2007 build years with similar maintenance histories and conditions of use. We have additionally screened EGR vs. non-EGR data to see if CJ-4 reduced wear better under conditions of higher soot loading. Again we didn't see a difference in our studies. It is very rough for my fleet clients to swallow the concept that because 20% of their fleet has DPF's they bought more expensive oil to protect these new vehicles, via the lubricant supplier's suggestion of consolidation/error proofing, and now they have to drop their OCI by over 15% across the board! When maintenance labor hours, equipment utilization and material costs get figured into this equation a very large negative variance is felt by a fleet with 1,000+ class 8 trucks.
