SAE J306 (Gear Oils)
Again, the classification is based on the lubricant viscosity measured at low and/or high temperatures. The high temperatures values are determined according to method ASTM D445. The low temperature values are determined according to method ASTM D2983 'Method of Test for Apparent Viscosity at Low Temperature using the Brookfield Viscometer' and are measured in mPa.s (c.P).
Multi-grade oil satisfies the viscosity requirements of one of the W grades at low temperatures and one of the non-W grades at high temperature.
It should be noticed that there is no relationship between the SAE engine oil and gear oil classifications. A gear lubricant and an engine oil having the same viscosity will have widely different SAE grade designation as defined in the two classifications.
