CJ-4 Diesel Oil: Yes or No?

Written by Dan Watson Friday, 18 December 2009 15:32

Several readers have asked whether they should use the new CJ-4 rated diesel oils. This seems simple considering the CJ-4 oils are backward compatible and qualified to replace all previous classifications of diesel oils. What might, on the surface, seem simple turns out to be a little more complex. First, if you have a 2007 or later diesel engine with the new pollution control systems (EGR & Soot Traps in the exhaust) you are required to use CJ-4 rated diesel oil. On the other hand, if you have a diesel engine that is not equipped with the new pollution control systems you may – but are not required to – use the new CJ-4 diesel oils.

So If You Can Use CJ-4 For All Diesel Engines Why Wouldn’t You?

My advice is to continue the use of CI-4+ rated oil in all models where CJ-4 oil is not specified in the owner’s manual. In order to meet the standards set by the EPA (to protect catalytic converters) the additive package for CJ-4 oils is less robust than CI-4+ oils. In a word, CI-4+ oils are stronger than CJ-4 oils and are well suited for your earlier model diesel engines. You cannot, I repeat, cannot, use CI-4+ oils in the diesel engines that require CJ-4; you will void the warranty and possibly damage the pollution control system. You will NOT damage any diesel engine by using CJ-4 oil, but CJ-4 will not be as robust as the CI-4+ oil. In a year or two the oil industry will find improved substitutes for the limited additives available for CJ-4 oils and employ them to make CJ-4 oils perform as well as CI-4+ oils.

A Word Of Caution

If you decide to go with my recommendation and stick with CI-4+ oil, do not purchase oils labeled CJ-4 and CI-4+. These oils are CJ-4 and have reduced additive packages but also qualify for the bare minimum CI-4+ specifications. Looking at tires, we can make the best analogy; you can buy radial tires that have similar physical characteristics but significantly different heat and load ratings. It is perfectly acceptable to say that a 4-ply tire can be used successfully where you have previously used a 6-ply tire; that doesn’t mean the 4-ply tire is as robust as the 6-ply tire. To insure you get the robust CI-4+ oils, look for oils labeled CI-4+ and not also labeled CJ-4. And if you have to use CJ-4 oils, I recommend you find a good quality synthetic oil.

Dan Watson, Certified Lubrication Specialist, STLE