Short answer
API CK-4 is a service category for oils used in high-speed four-stroke diesel engines, with first licensing on December 1, 2016. API describes it for engines meeting 2017 on-highway and Tier 4 off-highway emission standards as well as earlier model years, and says it can be used in engines that call for CJ-4, CI-4 PLUS, CI-4 and CH-4. CK-4 oils have an HTHS viscosity of at least 3.5 cP.
Why CK-4 replaced CJ-4
By the mid-2010s diesel engines were running hotter and at higher cylinder pressures to meet emissions and fuel economy rules. Engine makers asked for oils with more resistance to oxidation, better shear stability and better control of aeration (air entrained in the oil), which affects hydraulic components and bearing protection.
The resulting development program added new engine tests for oxidation and aeration and produced two categories at once: CK-4, which kept conventional viscosity, and FA-4, a lower-viscosity category for specific newer engines.
Fuel sulfur and aftertreatment
API says CK-4 oils are formulated for diesel fuel up to 500 ppm sulfur and are especially effective with diesel particulate filters and other aftertreatment. It also notes that running them on fuel above 15 ppm sulfur may affect aftertreatment durability or drain intervals, which matters for equipment used where higher-sulfur fuel is still sold.
Viscosity grades
CK-4 is not limited to particular grades. SAE 15W-40 remains the most common, with 10W-30, 5W-40 and others widely available. Every CK-4 oil must meet the 3.5 cP HTHS floor, which is what separates it from FA-4.
Engine maker specifications built on CK-4
Major diesel engine makers publish their own specifications that start from CK-4 and add tests or limits of their own, such as Cummins CES 20086, Detroit DFS 93K222, Volvo VDS-4.5 and Mack EOS-4.5. When a manual lists one of these, look for it by name in addition to the API donut.
Frequently asked questions
Can I use CK-4 in an older diesel?
API states that CK-4 oils can be used in engines that call for CJ-4, CI-4 PLUS, CI-4 and CH-4. Use the viscosity grade the manual lists for your climate.
Is CK-4 used in diesel pickups?
Many light-duty diesel pickups call for CK-4 or an engine maker specification based on it. The owner’s manual will list the grade and any required specification.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].