Get the lowdown on low-viscosity oils

As manufacturers roll out more choices, know how, when and where they can be used.

The Association of Equipment Management Professionals (AEMP) reports that it's been a year since the new CO2 emissions-busting diesel engine oils came to market. API’s Lubricants Group approved the new API CK-4 and FA-4 specifications to address the varying needs of engine technologies – aging, new, and in use, both on- and off-highway – and to help diesel engine manufacturers meet more stringent.

Last December, two new diesel engine oils began to make their way into the market place. This was the first time the category was split in two, defined by their High Temperature High Shear (HTHS) rate. The American Petroleum Institute’s (API) new diesel engine oil standards, API CK-4 and FA-4, were put in place to address the varying needs of engine technologies – aging, new, and in use, on- and off-highway – and to help diesel engine manufacturers meet more stringent emissions requirements.

Changes to the previous oil formulations, such as CJ-4, were driven by stricter CO2 regulations that were added to the list of EPA emission unmentionables. Specifically, the EPA wants the overall greenhouse gas emissions (CO2) reduced by 15 percent by the end of 2018. 

The new oils are designed to improve performance and lower emissions by providing enhanced protection against oil oxidation and engine wear, particulate filter blocking, piston deposits, and degradation of low and high-temperature properties. 

API CK-4 oils provide a number of improvements over CJ-4, including improved shear stability, oxidation resistance and aeration control. CK-4 is backward-compatible with CJ-4 and other formulations.

API FA-4 oils provide similar improvements over CJ-4 oils, but FA-4 oils are only intended for use in newer on-highway diesel engines. FA-4 oils are intended for new on-highway diesel engines and have limited or no backward compatibility with on- and off-highway diesel engines where engine manufacturers recommended CJ-4. While not specifically backward compatible, API says FA-4 oils are expected to play an important role in some current and new diesel engines by protecting those engines and at the same time helping them meet more stringent emissions requirements.

The major lubricant producers are bringing their versions of the CK-4 and FA-4 oils, so let's do a quick review of CK-4 and FA-4 specs and best practices in construction vehicles.


  • CK-4 can be used for current and older engines.
  • CK-4 oil is backwards compatible with CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 oils and is intended to be a replacement for CJ-4.
  • CK-4 offers superior wear and oxidation protection compared to CJ-4.
  • CK-4 has a minimum HTHS viscosity (3.5cP).
  • CK-4 is for both on-highway and non-road use.
  • CK-4 is available in viscosity grades SAE 15W-40, 10W-40, and 10W-30. Manufacturer's are now rolling out even lighter viscosity grades.


  • FA-4 is designed to accommodate higher temperatures and oil pressures in engines released after 2016.
  • FA-4 oil NOT backward-compatible with API CK-4, CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 oils because of lower HTHS viscosity.
  • FA-4 oils must pass same tests as CK-4 fluids.
  • FA-4 cannot be mixed with CK-4 or CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 oils. Diesel Oil recommends that FA-4 should not be used with diesel fuel with a greater than 15 ppm sulfur. 
  • FA-4 has the same wear and oxidation protection as CK-4, plus the potential to reduce greenhouse gas emissions due to its lower HTHS viscosity (2.9–3.2 cP)..
  • FA-4 is available in SAE 10W-30, 5W-30, and 0W-30, and like CK-4, lighter grades are being introduced by some manufacturers.

It is important to note that the API standards for CK-4 and FA-4 do NOT define suggested maintenance schedules. You need to talk with your engine manufacturer and/or service provider about changes to maintenance such as increasing the hours between drain intervals. And, always check with your vehicle engine's manufacturer for their recommendation for switching to either CK-4 or FA-4. Mention the word 'warranty' in your question to make sure the conversation includes what your dealer or manufacturer's rep says their company allows.

Low-viscosity oils

New engine technologies are calling for lower viscosity oils. The benefits of these advanced low-viscosity oils include energy loss, which can mean greater fuel efficiency. On-road reports show up to 2 percent increase in fuel efficiency in newer vehicles. 

Diesel Oil suggests older vehicles may not be suited for low-viscosity oil. Do an oil analysis test and work with your representative to evaluate if a lighter lubricant will help or hinder your machine.

Synthetic or synthetic blends of lower-viscosity lubricants have excellent shear, hydrolytic and thermal stability and enhanced cold start performance. 

This month, Phillips 66 and ExxonMobile introduced new full-synthetic CK-4 and FA-4 diesel engine oils to their lineups. 

ExxonMobil now has three Mobil Delvac 1-brand synthetic low viscosity heavy-duty diesel engine oils that meet the API standard. The Mobil Delvac 1 ESP engine oils meet or exceed the requirements of the API CK-4 specification and are backward compatible. The Mobile Delvac 1-brand products come in these configurations:

Mobil Delvac 1 ESP 5W-30 and ESP 5W-40 (CK-4): Formulated for newer and older engines, Mobil says this oil can extend oil drains for on-road vehicles up to 100,000 miles. Offers enhanced emission system protection in severe conditions and is designed especially for applications where the vehicle is operating in severe low-speed/heavy-load conditions.  Is compatible with vehicles using low-sulfur, as well as biodiesel fuel formulations. Mobil says in on-road urban conditions, it increased fuel economy by as much as 2.6 percent. Meets specification for many diesel-powered equipment from American and European manufacturers including some Caterpillar, Cummins, Mack and Detroit engines.

Mobil Delvac 1 Advanced Fuel Economy 5W-30 (FA-4) is a full synthetic, high-performance diesel engine oil that features an advanced low-ash formulation for protecting exhaust after-treatment systems, such as diesel particulate filter systems (DPF), selective catalytic reduction (SCR), continuously regenerating traps (CRT), diesel oxidation catalysts (DOC) and exhaust gas recirculation (EGR) systems. Mobil says this FA-4 oil was designed in particular to protect engine biofuels as it helps maintain engine cleanliness. The company recommends this oil for direct-injection or naturally aspirated and turbocharged, diesel-powered equipment. Currently, Delvac 1 Advanced Fuel Economy 5W-30 engine oil meets or exceeds the requirements of Cummins CES 20087 and Detroit Fluids Specification (DFS) 93K223.

Phillips 66 also rolled out a series of synthetic diesel engine oils that meet the new CK-4 and FA-4 standards, branded under the Phillips 66 Triton and Kendal SHP names.

Phillips 66 Triton Euro and Kendall SHP 5W-30 (CK-4): This formulation is backward-compatible for use in older diesel engines designed to meet 2007 EPA standards. It is specially configured to work with after-treatment systems using diesel particulate filters (DPF), diesel oxidation catalysts (DOC), or selective catalytic reduction (SCR) technology; on and off-road diesel only.

Phillips 66® Triton FE and Kendall SHP FE (FA-4): This formulation boasts outstanding soot control for protection against abrasive wear and sooty oil thickening, with excellent low-temperature pumpability with soot-laden oil. It was developed for new (2016 and newer) vehicles, specially formulated to protect exhaust after-treatment systems. The company say this FA-4 works with mixed fleets of diesel and gasoline fuel vehicles, and is certified for Cummins CES 20087 and Detroit Diesel DFS 93K223. Phillips says this oil can increase on-road fuel economy up to 3 percent. 

As always, talk with your supplier and equipment dealer for details specific to their model engines.