I often hear companies conversing about the relative pluses and minuses of the more recent API CJ-4 rated oils vs. the CI-4 rated diesel engine oils that came before. As a result, it seems that it would be a good idea for us to clarify a few things about the differences between the two oil types.nnMany of our customers are seeking our 15w40 viscosity AMSOIL synthetic diesel oil. Most often, this is either because they have some misgivings with regard to switching over to a “lower” viscosity oil or because they’ve been told “bad things” about the new CJ-4 oils.nnKey Additives Reduced in CJ-4 OilsnnIt is important to note, our AME 15w40 synthetic diesel motor oil does NOT meet API CJ-4 specs because in order to meet CJ-4 classification requirements motor oil blenders/manufacturers had to make significant reductions in the levels of key additives in acid fighting. That means that the TBN was lowered.nnAre Oil Drain Intervals Shortened?nnBecause the TBN of CJ-4 oils has dropped, many diesel owners are making the assumption that the extended drain capabilities of API CJ-4 oils should be much less as compared to the older CI-4 oils with better acid fighting ability in order to make the oils more compatible with Exhaust Gas Recirculation systems found on those vehicles sold as a 2007 model or beyond.nnExhaust Gas Recirculation units installed on 2007 model and newer diesels are leaving very HEAVY soot load on the lubricant in the crankcase. This has necessitated an increase in detergents and dispersants in the new CJ-4 oils – keeping things clean is always a good thing.nnMoreover, lesser quality CI-4 diesel engine oils (petroleum and “pseudo-synthetic” based) have had to implement upgrades to their basestock quality in order to meet CJ-4 specs. Thus, the CJ-4 oils are, in respects to their basestock, a higher quality lubricant. In contrast, if you’re comparing premium CJ-4 rated SYNTHETIC oils, the base stocks are likely pretty similar to their CI-4 predecessors since the original basestocks used for the CI-4 rated oils were likely already able to meet CJ-4 classification requirements.nnAs evidenced in the previous paragraphs, there have actually been numerous improvements made in converting from CI-4 to CJ-4 rated oils. n fact, the only drawback I can really see to moving from a CI-4 rated oil to a CJ-4 rated oil IS the potentially shorter drain intervals due to the lower TBN of such oils. However, if you don’t take your vehicles to the limit of your oil anyway, then you won’t likely notice the difference.nnIt is actually quite common for diesel owners to drain their oil long before it is necessary. In most cases, this is simply because they fear that longer drain intervals will not effectively protect their expensive engines. So, even though the CI-4 15w40 oil MIGHT offer a longer drain than our CJ-4 5w40, it’s likely that most end users will not notice because they never take their oil to the limit anyway.nnAlso important to note is that CJ-4 users’ oil analysis results are beginning to paint a picture which suggests CJ-4 oils, although lower in INITIAL TBN, may have the ability to RETAIN their acid fighting ability better than their CI-4 predecessors. Thus, it is possible that, even with the lower initial TBN, the CJ-4 oils may still offer similar drain interval capability. Only time and more testing will show this for sure.nnThe end result: If you don’t intend on trying to extend your oil drain intervals beyond what is typical, and even if you do, you may not be at all affected by the lowering of the TBN values for CJ-4 oils. Even better, increases and improvements in the additives related to wear protection and detergency of a CJ-4 oil will be of benefit to you. Hence, for many companies and individuals owning diesel engines, the CJ-4 rated oil COULD actually prove to be the best option, whether you have a newer model diesel or not.