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What you need to know to select the proper oil for your diesel engine

Wednesday, November 1, 2017 - 06:00
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There is no shortage of challenges for those who design the vehicles we drive. Ever-tightening safety and emissions regulations, combined with increasing customer demands, keep automotive engineers continually on their toes. The moment one problem is conquered, they are sent back to the drawing board to deal with the next pressing issue. This has led to vehicles being designed in a more holistic manner, because the “low-hanging fruit” has already been harvested. For any given problem that needs solving, progressively more vehicle systems become candidates for redesign.

Lubricant engineers are not exempt from this dynamic. Engine lubrication is an example of a system that has sometimes been viewed in narrow terms. No one would deny that oil is the lifeblood of the internal combustion engine, however, it is now widely recognized that it plays a critical role in fuel economy as well. Fuel economy has always been important to the diesel engine manufacturers, but their hand is now being forced with the advent of greenhouse gas (GHG) emissions regulations. This issue has gained importance in recent years because fuel economy is directly related to the production of CO2, which is considered to be a greenhouse gas. And now, like never before, engine oil is playing an increasingly important role in meeting those regulations, as well as lowering the total cost of ownership to the vehicle owner.

(Photo courtesy of Shell Lubricants) Diesel engine oil has undergone another transformation with the development of the PC-11 category, which includes the CK-4 and FA-4 specifications.

Diesel engine oil has been taken to a higher level of performance with the development of new American Petroleum Institute (API) specifications known as API CK-4 and FA-4, which were officially released for licensing on Dec. 1, 2016. There are some important changes that the diesel engine owner should be aware of regarding this new category of oils, and this information can help them choose the correct engine oil for their specific application.

An historical perspective

Big changes were afoot for on-road diesel engines leading up to the 2007 model year. The diesel particulate filter (DPF) was being widely adopted as a solution in order to comply with new EPA regulations regarding particulate matter (PM) emissions. The DPF wasn’t a bolt-on fix; there were numerous changes that had to take place in fuel and lubricant technology to make it all work. First, sulfur had to be virtually eliminated from diesel fuel because it disabled the catalyst coating found on most DPFs. The allowable sulfur limit had been 500 parts per million (ppm), now it was being lowered to 15 ppm. Diesel engine oil additive formulations would also have to change. For decades, engine oil blenders had made extensive use of an additive known as ZDDP, which contains zinc and phosphorous for anti-wear protection. Sulfated ash is also used to increase the total base number (TBN) of the oil. These metals formed part of the PM emissions of the engine and would collect as ash in a DPF, thereby shortening the DPF service life.

To address these and other issues, API developed the PC-10 category for diesel engine oils, which led to the release of the CJ-4 specification in 2006. Among other improvements, CJ-4 placed chemical limits on the use of phosphorous and sulfated ash in diesel engine oil in order to extend the service life of DPFs. CJ-4 was backwards compatible with previous diesel engine oils, and met the requirements that had been established with CH-4, CI-4 and CI-4+. All 2007 and newer on-road diesel engines required the use of CJ-4, which became the standard for more than 10 years.

(Photo courtesy of Shell Lubricants) CK-4/FA-4 oils are formulated for better aeration control, increased oxidation resistance, and improved shear stability.

The advent of CK-4 and FA-4

While discussions concerning a new diesel engine oil category started shortly after CJ-4 was introduced, work on the new diesel engine oil specification began in December 2011 with the formation of the New Category Development Team (NCDT), chaired by Dan Arcy, Global OEM Technical Manager for Shell Lubricants. The NCDT committee consisted of members from the API Lubricants Group, Truck & Engine Manufacturers Association (EMA), American Chemistry Council (ACC), and representatives from the major engine manufacturers. The NCDT’s main objectives were to improve specific aspects of diesel engine oil performance, as well as to provide a tool for engine manufacturers to meet the 2017 EPA regulations regarding greenhouse gas emissions.

The NCDT’s work on the new category, initially identified as PC-11, evolved into the development of two sub-categories, PC-11A and PC-11B, which then became known as CK-4 and FA-4. CK-4 is a direct replacement for CJ-4, and while it has improved performance, it is also engineered to be backwards compatible. CK-4 is available in multiple viscosities, including XXW-40 and XXW-30 (by way of explanation, XXW-30 includes 0W-30, 5W-30, and 10W-30). FA-4, on the other hand, is specifically formulated as an oil with lower viscosity and is only available as a XXW-30 grade. FA-4 is not backwards compatible and would only be used if specifically recommended by the diesel engine manufacturer.

(Photo courtesy of Shell Lubricants) The difference between CK-4 and FA-4 is viscosity.  FA-4 engine oil has a lower High-Temperature, High-Shear viscosity and is able to achieve increased fuel economy and lower GHG emissions.
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