See Figures 1 and 2
When adding oil to the crankcase or when changing the oil and filter, it is important that oil of an equal or higher quality than the original be used in your car. The use of inferior oils may void your warranty. Generally speaking, oil that has been rated SF by the American Petroleum Institute will prove satisfactory.
Oil of the SF variety performs a multitude of functions in addition to its basic job of reducing friction of the engine's moving parts. Through a balanced formula of polymeric dispersants and metallic detergents, the oil prevents high temperature and low temperature deposits and also keeps sludge and dirt particles in suspension. Acids, particularly sulfuric acid, as well as other products of combustion of sulfur fuels, are neutralized by the oil. These acids, if permitted to concentrate, may cause corrosion and rapid wear of the internal parts of the engine.
It is important to choose an oil of the proper viscosity for climatic and operational conditions. Viscosity in an index of the oil's thickness at different temperatures. A thicker oil (higher numerical rating) is needed for high temperature operation, whereas thinner oil (lower numerical rating) is required for cold weather operation. Due to the need for an oil that embodies both these characteristics in parts of the country where there is wide temperature variation within a small period of time, multigrade oils have been developed. Basically a multigrade oil is thinner at low temperatures and thicker at high temperatures. For example, a 10W-40 oil exhibits the characteristics of a 10 weight oil when the car is first started and the oil is cold. Its lighter weight allows it to travel to the lubricating surfaces quicker and offer less resistance to starter motor cranking than, let's say, a straight 30 weight oil. But after the engine reaches operating temperature, the 10W-40 oil begins acting like a straight 40 weight oil, with its heavier weight providing greater lubricating protection and less susceptibility to foaming than a straight 30 weight oil. Whatever your driving needs, the oil viscosity/temperature chart should prove useful in selecting the proper grade. The SAE viscosity rating is printed or stamped on the top or side of every oil container.