I respectfully disagree that oil was being improved by API specifications and manufacturers up to CJ-4 and then took a step backwards. The environment that the oil must perform in has changed dramatically in just the past few years. With the increase in EGR, retarded timing, multiple injection events (both for increased power and regeneration cycles), and other changes the heat load on the entire engine and related systems has been increased dramatically. This creates a much less hospitable environment for the oil and increases the performance demand in multiple ways on it. This is the reason for the new lubricants and coolants, also.
Assuming that you are correct, this would mean that API and the oil manufacturers conspired to produce a product that does not perform as well and will cost the consumer. Not only in the cost of the product, since CJ-4 tends to be more expensive that CI-4+, but in downstream costs of operation, increased oil consumption, increased repair cost, and shortened engine life. How many manufacturers bring a premium product to market that is inferior to their predecessor product? What would that benefit? They will surely be the loser in the end when the consumer, from single pickup truck owner to the mega fleet owner, finds this out.
I have read the articles and respect John Martin's analysis. I hear what you are saying and also respect your opinion. However, I disagree. There have been 10's of thousands of hours in test cells and millions of miles of over the road testing and CJ-4 out performs CI-4+ in the engines that spec CJ-4. With that said, when you remove or modify your emission system then you have become your own warranty and repair station. The money that you save on the oil you will be able to apply to the repair of your engine.
Just to be clear here. For those of you who have not removed any of the downstream emission control equipment on your trucks, there is no benefit to using CI-4+ engine oil. On the contrary, use of this API spec will cause premature plugging of elements and eventual damage. This will not happen immediately upon installation of the oil but will happen over time.
Thanks, Mikey, for your input. In no way am I attempting to argue, just to bring light to the subject
Paul