Viscosity and Viscosity Measurement

PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 2/TASK 2

(c) SC. Meets all automotive manufacturers' requirements for vehicles

manufactured from 1964 to 1967.

(d) SD. Meets all automotive manufacturers' requirements for vehicles

manufactured from 1968 to 1970. SD oil offers additional protection over SC oils,

necessary with the introduction of emission controls.

(e) SE. Meets all automotive manufacturers' requirements for vehicles

manufactured from 1971 to 1979. Stricter emission requirements during these years

created the need for this oil to provide protection.

(f) SF. Meets all automotive manufacturers' requirements for vehicles

manufactured after 1980. SF oil is designed to meet the demands of the small,

highrevving engines made necessary by the trend toward smaller vehicles. An SF

oil can be used in all automotive vehicles. API service ratings have related

military specification designations.

c. Viscosity and Viscosity Measurement.

(1) General. The viscosity of an oil refers to its resistance to flow. When oil

is hot, it will flow more rapidly than when it is cold. In cold weather,

therefore, oil should be thin (low viscosity) to permit easy flow. In hot weather,

oil should be heavy (high viscosity) to permit it to retain its film strength. The

ambient temperature in which a vehicle operates determines whether an engine oil of

high or low viscosity should be used. If, for example, too thin an oil were used

in hot weather, consumption would be high because it would leak past the piston

rings easily. The lubricating film would not be heavy enough to take up bearing

clearances or prevent bearing scuffing. In cold weather, heavy oil would not give

adequate lubrication because its flow would be sluggish; some parts might not

receive oil at all.

(2) Viscosity Measurement. Oils are graded according to their viscosity by a

series of Society of Automotive Engineers (SAE) numbers. The viscosity of the oil

will increase progressively with the SAE number. An SAE 5 oil would be very light

(low viscosity) and an SAE 90 oil would be

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