American Petroleum Institute. The primary oil and natural gas trade association in the United States. API operates a voluntary licensing and certification program that allows engine oil marketers to use the API Engine Oil Quality Marks if their products meet specific requirements. CD was first introduced in 1955 for certain indirect-injection, naturally-aspirated, turbocharged or supercharged diesel engines running on fuels with a wide quality range (including high-sulfur fuels). Oils designed for this service have requirements for corrosion, piston deposits and soot handling.
API has discontinued licensing diesel engine oils against API CD and it is considered to be a obsolete specification.
Engine lubricants claiming to meet API CD are still marketed in some regions around the world. These oils are typically formulated to be SAE 15W-40 or heavier and are unlikely to be suitable for use in the majority of engines. Refer to engine manufacturer recommendations to determine if API CD oils are suitable for use in a specific application.
For more information on API CD, contact your Lubrizol representative.