See Figure 1
The SAE (Society of Automotive Engineers) grade number indicates the viscosity of the engine oil, and thus its ability to lubricate at a given temperature. The lower the SAE grade number, the lighter the oil. The lower the viscosity, the easier it is to crank the engine in cold weather. Oil viscosities should be chosen for the lowest anticipated temperatures during the oil change interval. Multi-viscosity oils (10W-30, 20W-50, etc.) offer the important advantage of being adaptable to temperature extremes. They allow easy starting at low temperatures, yet give good protection at high speeds and engine temperatures. This is a decided advantage in changeable climates or in long distance touring. The API (American Petroleum Institute) designation indicates the classification of engine oil for use under given operating conditions. Oils designated for use Service SF or SG (or a superseding rating) should be used. Oils of the SF or SG type perform a variety of functions inside the engine in addition to the basic function as a lubricant. Through a balanced system of metallic detergents and polymeric dispersants, the oil prevents the formation of high and low temperature deposits, and also keeps sludge and dirt particles in suspension. Acids, particularly sulfuric acid, as well as other by-products of combustion, are neutralized. Both the SAE grade number and the API designation can be found somewhere on the container.
Non-detergent or straight mineral oils must never be used.
Oil must be selected with regard to the anticipated temperatures during the period before the next oil change. Using the chart, select the oil viscosity prior to the next oil change for the lowest expected temperature and you will be assured of easy cold starting and sufficient engine protection.
See Figure 2
Engine oils should be selected from the accompanying chart. The SAE viscosity number should be chosen for the lowest anticipated temperature at which the engine will be required to start, not for the temperature at the time the oil is changed. Use only oils designated by the API (American Petroleum Institute) for service CC or CD (or a superseding rating). The letters should appear somewhere on the oil can for example "SF/CC" or "SG/CD". This indicates that the oil provides protection from rust, corrosion and high temperature deposits in diesel engines in moderate to severe service.