Viscosity Requirements for API CK-4 and API FA-4
by Kevin Pfile Business Development, Western Region and Mexico

In 2011 the American Petroleum Institute (API) began work on the replacement of the API CJ-4 designation and the development of the next generation heavy-duty diesel engine oils under the designation of Proposed Category 11 (PC-11). The goal was to provide the industry with oil blends that would provide better wear protection, greater oxidation stability and longer oil life in high temperature/high shear (HT/HS) operating conditions. To comply with regulatory changes and to lower business costs it was also critical to develop oils to help reduce CO2 emissions and increase fuel efficiency on new engines.

Engine oil viscosity is measured a few different ways. In-service oil analysis measures the Kinematic viscosity which is a measure of a fluids resistance to flow. The values are in centistokes and are measured at 100C. Engine oil manufacturers will measure the viscosity of the new oil in order to determine the grade. For multigrade engine oils the first number in the grade will represent two values; the cold cranking simulation viscosity and the cold pumping viscosity. These measurements use special instrumentation which bring the oil temperature down below 0C in order to understand the absolute viscosity shear rate measured in centipoise at very low temperatures. This value is recorded as the first number in the grade of the oil of the “W” designation for “winter grade”. The second number in the grade represents the Kinematic viscosity at 100C. The new API classifications addresses the viscosity behavior at elevated temperatures. The new grades will be qualified according to their absolute viscosity at high temperature and high shear at 150C. These grades are licensed as API CK-4 and API FA-4.

The API CK-4 lubricants have traditional kinematic viscosity grades 15W40, 10W30, 5W40, and 5W30 yet differ at high temperature high shear viscosity measurements. This formulation is backwards compatible for existing high-speed four stroke diesel engines and can be safely used in place of API CJ-4 products. API FA-4 lubricants have 10W30 and 5W30 grades. This formulation is not backwards compatible and not suitable for use in current diesel engines. This category will be used for diesel engines that are currently in development stages for future release. It is critical to consult the manufacturer prior to use of API FA-4 lubricants.

Both oil categories will provide the ability for end users now and in the future the option to choose lower viscosity grades and in turn increase fuel efficiency. To accomplish the ability for end users to safely choose lower viscosity grades, the oil industry turned to a combination of base oils and viscosity index improvers. A key viscosity index improver utilized was sheer resistant polymers which allow engines to operate safely with a thinner viscosity grade. This lighter, thinner viscosity grade improves the speed at which machines are able to operate while using the same amount fuel all without sacrificing the necessary lubrication protection. As a result the decrease in fuel consumption leads to smaller amounts of CO2 that are emitted into the atmosphere.

Oil analysis is crucial for monitoring oil and engine performance as fleets’ transition from the older to newer formulations. ALS can assist with customizing test slates to address concerns.