Write a short note on: SAE ratings of lubricating oils.

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written 8.5 years ago by

teamques10 ★ 68k

SAE (Society of Automotive Engineers) ratings classify lubricating oils according to their viscosity. The method assigns a number to an oil whose viscosity at a given temperature falls in a certain range.
In order to assign the numbers two temperatures are used as reference: one is -18°C (0°F) and 99°C (210°F).
Oils defined in terms of viscosity at -18°C, such as SAE 5W, 10W and 20W grades, provide starting in cold climates easy.
Oils defined in terms of viscosity at 99°C, such as SAE 20, 30, 40 and 50 grades, work satisfactorily in normal and hot climates.
These numbers merely classify the oils and are not indicators of the oil quality.
Some oils, called multi-grade oils, are developed to exhibit more than one viscosity at different temperatures. Eg. SAE 20W/50 oil has viscosity equal to SAE 20W at -18°C and viscosity equal to SAE 50W at 99°C.

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