Short answer
API CI-4, introduced in 2002, was written for high-speed four-stroke diesels meeting the emission standards that took effect that year, many of them using exhaust gas recirculation (EGR). API CJ-4, finalized for licensing in October 2006, targeted the engines with diesel particulate filters that followed, and it was the first U.S. diesel category to cap sulfated ash, phosphorus and sulfur. API CK-4, from December 2016, can be used in engines that call for either.
CH-4 and CI-4: the EGR era
API CH-4 was introduced in 1998 for engines meeting 1998 emission standards. CI-4 followed in 2002, established in late 2001, for engines meeting standards implemented in 2002. API describes CI-4 oils as formulated to sustain durability where EGR is used, and designed for fuel with up to 0.5% sulfur by weight.
EGR routes exhaust back into the intake, which loads the oil with more soot and acids. CI-4 PLUS was a later, tougher designation for soot-related viscosity increase, and some CI-4 oils also qualify for it.
CJ-4 and the chemical limits
Diesel particulate filters collect ash that cannot be burned off, and that ash comes partly from oil additives. To protect the filters, CJ-4 capped sulfated ash at 1.0%, phosphorus at 0.12% and sulfur at 0.4% by weight, and set a 13% NOACK volatility limit.
API describes CJ-4 as formulated for fuel up to 500 ppm sulfur, with the caution that using fuel above 15 ppm may affect aftertreatment durability or drain intervals.
Where these categories stand now
API still lists CJ-4, CI-4 and CH-4, but CK-4 is the current heavy-duty category, and API says CK-4 exceeds their performance and can lubricate engines that require them. Fewer oils are licensed to the older categories alone today.
Older equipment that calls for them
Tractors, generators, construction machines and pickups from the late 1990s through the 2000s often list CH-4, CI-4 or CJ-4 in the manual. A CK-4 oil in the specified viscosity grade is the usual modern choice. Engines running higher-sulfur fuel outside North America may need different guidance, so check with the engine maker.
Frequently asked questions
My manual says CI-4. Can I use CK-4?
Yes, API states that CK-4 can be used in engines requiring CI-4, as well as CJ-4, CI-4 PLUS and CH-4. Match the viscosity grade the manual lists.
Can FA-4 replace CJ-4?
No. API states FA-4 is not backward compatible with CJ-4 or the earlier categories.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].