June 15th 2009 API CJ-4 vs. CI-4: Is One Diesel Oil Spec Better than the Other?
It is common to hear individuals talking about the relative benefits and drawbacks of the vs. the older CI-4 diesel engine oils. So, it seems a good idea for us to discuss a few issues regarding the differences between the two oil types.
Many of the visitors to our AMSOIL website are seeking our AMSOIL AME 15w40 Synthetic Diesel Oil. Generally, this is either because they fear switching over to a “lower” viscosity oil or because they’ve been told “bad things” about the new API CJ-4 oils.
Reduction of Key Additives in API CJ-4 Rated Oils
It should be noted that, our AME 15w40 synthetic diesel oil has not been blended to meet the latest CJ-4 specs because to meet CJ-4 specifications motor oil producers were required to make significant reductions in the levels of key additives in fighting acid - and thus corrosion within the engine. In other words, they lowered the Total Base Number of the oil.
Are Oil Drain Intervals Shortened?
Because the TBN of CJ-4 oils has dropped, it is assumed that the long oil change abilities of API CJ-4 oils have been compromised as compared to CI-4 oils with higher Total Base Number in order to blend a diesel oil that is more likely compatible with the new EGR systems found on those vehicles sold as a 2007 model or beyond.
Current EGR systems are placing extremely HEAVY soot load on the oil. As a result, oil manufacturers have increased the dispersant and detergent additives in the new CJ-4 oils - a good thing, obviously.
In addition, lower grade CI-4 diesel motor oils (petroleum based and low grade synthetics) have had to implement upgrades to their base stock quality in order to adequately meet CJ-4 classification specs. As a result, the newer API CJ-4 oils are, in respects to their basestock, a more advanced lubricant. In contrast, if premium synthetic oils are being compared, the base stocks are most likely very similar to or even identical to their CI-4 predecessors because the basestocks used for the CI-4 rated oils were likely already plenty capable of meeting CJ-4 classification requirements.
So, in many respects CJ-4 oils ARE an improvement over CI-4 oils. The only POTENTIAL drawback to using a CJ-4 oil is a shorter oil drain. But, you may very well not even notice the difference between a CI-4 and a CJ-4 rated oil if you typically don’t extend your drain intervals all that far.
It’s actually very common for users to change their oil before it’s really necessary simply because they don’t trust the longer drain intervals to protect their expensive engines. So, in the end, although it is POSSIBLE that a CI-4 rated oil could offer a longer oil drain interval due to higher TBN levels, many users won’t be affected by the shorter drain, since they don’t extend their oil drain intervals anyway.
Moreover, oil analysis results of many CJ-4 users seem to show that, although the initial TBN of CJ-4 oils is lower, TBN “retention” for these CJ-4 oils may actually be BETTER than CI-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 won’t likely be trying to take your oil to the max drain intervals possible, you likely will not be negatively affected by any potential shortening of oil drain intervals with CJ-4 oils. On the flip side, wear protection and detergency of a CJ-4 oil can only help make the switch to a CJ-4 oil a beneficial one. Hence, for many companies and individuals owning diesel engines, the API CJ-4 rated oil MAY actually be the better choice, whether you have a newer model diesel or not.