#### TYPES OF ENGINE OIL

Engine oil service classifications have been provided by the American Petroleum Institute and include "S" (normal gasoline engine use) and "C" (commercial and fleet) applications. The following chart compares the latest API oil classifications with those previously used.

The American Petroleum Institute (API) SH quality level is a performance upgrade for gasoline engine oils from the API SG category. The American Society for Testing and Materials (ASTM) establishes engine tests for motor oils. Passing limits for these tests are the same for API SH oils as they were for API SG lubricants. However, the Chemical Manufacturers Association (CMA) has applied a Multiple Test Acceptance Criteria (MTAC), which is a statistically based methodology, to ASTM engine tests used to evaluate candidate oil.

The MTAC is:

- For oil run once, test data for each parameter must be a pass.
- For oil run twice, the average value of each parameter must be a pass.
- For oil run three or more times, one test may be discarded, and the average value of retained test data for each parameter must be a pass.

  Previously for API SG and earlier categories, a pass in each engine test was sufficient regardless of the number of failures on the candidate oil before a test pass was obtained. Therefore, oils could be approved by failing a number of tests and bouncing one through for a pass.

  In order to be certain that API SH oils can pass the ASTM engine tests to which MTAC have been applied, higher additive levels and a balancing of the chemical additive formula are required. More highly refined base oils are also helpful in meeting API SH specifications. The MTAC applied to ASTM engine tests results in performance improvements outlined below.