With the creation of two diesel engine oil categories a few years ago and with a growing number of viscosities for diesel engines, fleets need to be aware of the new types of oils—API CK-4 and API FA-4—and the differences between them.
CK-4 provides improved shear stability, oxidation resistance, and aeration control over CJ-4 in the familiar SAE 15W-40 and 10W-30 viscosity grades. FA-4 provides similar protection to CK-4 oils, but in lower viscosity grades to meet the needs of next-generation diesel engines beginning with the 2017 model year. FA-4 oils meet the same performance measures as CK-4 but they also help increase fuel economy in engines designed for the lower viscosity FA-4 grades. Key improvements to the new oils include the following:
This is the resistance of oil molecules to shearing or breaking down under extreme stress inside the engine. Shear causes oil to decrease to a lower viscosity, and excessive viscosity loss could affect how well the oil can protect the engine. CK-4 and FA-4 oils will have improved shear stability compared to CJ-4 oils.
Oil oxidation is one of the main reasons for oil breakdown, and it occurs more readily under higher engine operating temperatures. With many newer engines running hotter, CK-4 and FA-4 standards deliver improved oxidation stability versus CJ-4 oils.
This is the entrainment of air bubbles in the oil, which can limit the ability for oil to cool and protect the engine. Newer engines with higher operating temperatures and pressures can increase the amount of air trapped in oil. As oil is more regularly used as a hydraulic fluid for valve-train actuation, this task can be compromised by aerated oil. CK-4 and FA-4 oils provide greater protection against aeration.
You may have heard of the term high temperature high shear (HTHS) as the new oils were being developed. CK-4 oils are being called High HTHS engine oils because their viscosities are the same as those found in CJ-4 oils. In contrast, FA-4 oils are being called Low HTHS oils because their viscosities are lower. These Low HTHS oils were developed to provide engine manufacturers with a tool that will help them meet more stringent fuel economy and greenhouse gas emissions requirements.
This article was contributed by Kevin Ferrick, the director of product programs for the American Petroleum Institute.