-Engine Oil Function The oil that circulates through an engine plays an important part in engine life. Not only does it lubricate the fast moving parts of the engine to reduce friction and wear, but it must also cool, clean, cushion, protect, and seal various parts within the engine. Motot oil is identified in two ways: by its American Petroleum Institute(API) Service Classification, and its Society of Automotive Engineers (SAE) Viscosity Grade.
Service Classifications The API Service Classification is a two letter designation based on the oil's performance. Oils for use in gasoline engines have an "S" followed by a letter from "A" to "G". Classifications SA, SB, SD, and SE were used in eariler cars but are unsuitable for models built after 1979. SF oils were designed for use in most 1980 and later cars and can be substitued for SC, SD, and SE oils. SG is the latest Service Classification. Oils in this group were designed for use in 1989 and later gasoline engine cars, but can be substitued for SE and SF oils. SG oils provide better engine protection than the other categories. Motor oil classifications can be found printed on the top or side of the oil container, along with viscosity ratings.
Viscosity Grades The SAE Viscosity Grade is a numerical designation of an oil's resistance to flow. A thin oil that flows easily has low viscosity. A thick oil that does not flow easily has a high viscosity. Lower numbers represent thinner oils, and higher numbers represent thicker oils. Viscosity numbers are used for both single and multigrade oils. Single grades have a single number, such as SAE 30. Multigrade oils have a dual designation, such as SAE 10W-30. A "W" suffix indicates the oil meets certian viscosity requirements at low temperatures. Oils without the "W" meet certian viscosity requirements at high temperature. Multigrade oils meet both the low and high temperature specification. For maximum engine life and to maintain your vehicle's warranty, use oil with proper service classification and viscosity at the recommended time and mileage intervals. Check your vehicle owner's manual for this information.