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I often hear companies arguing the relative benefits and drawbacks of the newer CJ-4 diesel engine oils vs. the older CI-4 diesel motor oils. So, why don’t we spend a few minutes explaining why you might or might not want to utilize a CJ-4 or CI-4 rated diesel motor oil in your engine(s).

Many 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.

Key Additives Reduced in CJ-4 Oils

It is important to note, our AME 15w40 synthetic diesel engine 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.

Extended Drains Compromised?

As a result of these changes in TBN of CJ-4 oils, many diesel owners are making the assumption that the extended drain capabilities of CJ-4 oils have been compromised as compared to CI-4 oils with higher TBN values in order to blend a diesel motor oil that is more likely compatible with EGR systems found on those vehicles sold as a 2007 model or beyond.

Exhaust 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.

Moreover, lesser quality CI-4 diesel motor 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.

As 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.

Chances are good that you are one of the many users that change their oil long before it’s necessary, simply because they don’t trust their oil to “go the distance”. Thus, it’s entirely possible that users may never even notice the potentially shorter CJ-4 drain interval, since they’ve never extended their oil drains with CI-4 rated oils.

In addition, there seems to be evidence that, although the starting TBN value of the CJ-4 oils is lower than CI-4 oils, TBN “retention” seems better with the CJ-4 oils. If these initial oil analysis results are proven true by continued field testing, we MAY find that CJ-4 oils are able to offer oil drain intervals similar to higher TBN CI-4 oils.

The 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.