Test Precision, Base Oil Interchange and Viscosity Read Across

Additional measures to ensure test precision and variable analysis

The new tests developed to support the GF-5 specification process are subject to analysis to verify their accuracy and precision. To do so, the American Petroleum Institute (API) uses a precision matrix and Round Robin testing.

A precision matrix consists of a series of tests to determine repeatability and reproducibility of a test procedure including bench, chemical, physical, and engine performance tests.

Round Robin testing involves sharing a set of samples with participating laboratories to evaluate repeatability and reproducibility of a test procedure.

It is also necessary to determine how test outcomes are changed by formulation variables including base oils and viscosity grades. These determinations result in the Base Oil Interchange (BOI) and Viscosity Grade Read Across (VGRA) guidelines that are established by the API BOI/VGRA committees. These committees are made up of technical experts from additive companies and oil marketers. Automotive OEMs are also invited to participate.

Base Oil Interchange is determined by running a Matrix of tests with all factors remaining constant except the base oil. This testing can determine the effect of varying base oils on test results. This information helps oil manufacturers ascertain how certain base oils will affect a formulation's performance and whether these formulations will qualify as GF-5. The same basic principle applies to the Viscosity Grade Read Across. Test Matrix is conducted using various viscosity grades to determine the effect of change on the result and what viscosity grades will qualify for GF-5. This data is analyzed and made available to oil marketers and additive companies to assist in formulation decisions along with the design of the oil qualification test program.