Oul Classifications

Press, Volume CIV, Issue 30738, 30 April 1965, Page 9

Oul Classifications

ALTHOUGH many motorists x are aware of the designation of motor oils by viscosity, only few know there exists a system of classifying oils into categories of suitability for use in conditions of varying severity. Because of the rapid developments in engine design and construction, by the early 1950’s some additive type oils were available to the motorist; oils which contained different types and concentrations of additives, each of which improved performance in different ways. Motor oils had then become tailored to match the engine. Because of this, the American Petroleum Institute, working closely with representatives of the motor industry, considered it necessary to de. fine different degrees of sever-

ity in engine service. These classifications, of which there are three, are indicated as “ML,” “MM,” and “MS,” the latter denoting the most severe type of service. While this “A.P.1.” classification scheme provides a useful definition of service conditions, it does not provide a yardstick against which the performance of oils can be measured. Seeing the need for this, the motor manufacturers iri the United States devised a series of laboratory engine tests to simulate the most severe service described in the “MS” service classification.

These tests, of which there are five, were announced in 1956, and are revised from time to time to take into account advances made in the

petroleum and automotive industries.

The standards set by the “MS” tests are very high and any oil that meets the minimum requirement is undoubtedly a first-class motor oil. The tests are not just pass or fail procedures, but provide margins in the more critical requirements of each test to permit easy assessment by laboratory technicians of whether an oil is well up or down the scale. In one way, therefore, the tests provide for a grading of oils from poor to outstanding, the latter indicating an oil which provides the motorist with the maximum insurance against engine failure through inadequate lubrication. Gone are the days when any oil would do: