The American Petroleum Institute (API) designation indicates the classification of engine oil for use under given operating conditions. While modern lubrication technology has led to updated classifications such as "Service SE'', "Service SF'' and "Service SG'', most 1978–88 vehicles covered by this manual only require oil with a "Service SD'' designation. Exceptions include the 1986–88 RX-7 and 1988 323 (DOHC engine only), for which Mazda recommended a fuel efficient SF grade. Mazda also recommended against the use of synthetic oil in 1986–88 RX-7 models. 1989 vehicles covered by this manual require oil with a "Service SF'' designation. In any case, it is OK to use oil with a newer classification (such as "Service SG''), that has superseded earlier grades. Oil of these types 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 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.
The Society of Automotive Engineers (SAE) 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 (or viscosity), the lighter the oil; the higher the SAE grade number (or viscosity), the heavier the oil. Since lighter oil has a reduced resistance to flow, it is easier to crank an engine filled with low viscosity oil in cold weather. Warm weather, on the other hand, requires heavier (higher viscosity) oil for adequate protection.
| Fig. 1: Engine oil viscosity chart for 1986–89
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Multi-viscosity oils 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. Oil viscosities should be chosen from those oils recommended for the lowest anticipated temperatures during the oil change interval.
NOTE: Both the SAE grade number and the API designation can be found on the label of the oil container.
Non-detergent or straight mineral oils must never be used. Also, do not use oil that is unlabeled or which has been reprocessed. Oil viscosity should be chosen on the basis of the range of temperatures you expect during the time the oil will be in the crankcase. You need not change oil because of a short period of unusual temperatures. Temperature ranges and related viscosities for most 1978–85 vehicles are as follows:
NOTE: For 1986–89 models, the viscosity limits have been slightly modified. See the accompanying illustration.
All engines with catalytic converters require the use of unleaded fuel exclusively, as leaded fuel will almost immediately destroy the effectiveness of the catalytic converter. Unleaded fuel minimizes the accumulation of carbon deposits and corrosion in the engine and exhaust system, thus offering further benefit.
