As CK-4 engine oils get closer to arriving you may hear the term High Temperature High Shear (HTHS) viscosity. CK-4 oils are being referred to in the industry as “High HTHS” engine oils. FA- 4 oils are being referred to as “Low HTHS” oils. These Low HTHS FA-4 oils are being designed to provide fuel economy above and beyond current CJ-4 and CK-4 oils through the use of thinner viscosity fluids.
Shear stability is the ability of the oil molecules to resist shearing under severe stress inside the engine. Oil shearing results in a lower viscosity, and excessive viscosity loss could impact the ability of the oil to protect vital engine parts. The new CK-4 standards call for improvements in shear stability versus CJ-4 oils. New, more stringent shear stability test limits are being developed to validate that each oil’s shear stability meets the new guidelines.
Oxidation is one of the primary causes of oil breakdown and is accelerated by higher operating temperatures. The next generation of engines are being designed to run hotter. So, CK-4 standards call for improved oxidation stability versus CJ-4 oils.
The new CK-4 standards call for improvements in aeration control. Aeration is when the engine oil starts to develop tiny air bubbles, foam or both, which can impede the oil’s ability to protect the engine. To monitor the effectiveness of the new oils, they will have to pass a new aeration test called the Caterpillar Engine Oil Aeration test.