Engine oil should be selected based on viscosity and type. External environment, operating temperature and engine mileage are all factors that need to be considered in order to select an oil that will provide superior lubrication and protection for moving parts and internal engine components.
Vehicle manufacturers typically suggest two or more motor oil viscosities in order to ensure that an engine remains properly lubricated during different conditions. Viscosity is a measure of a fluid's resistance to flow. An engine oil's viscosity is usually notated using two digits, with lower numbers corresponding to oil that is less viscous. The first digit of this notation is followed by a "W" and is used to indicate the flow of an oil at 0 degrees Fahrenheit. The second digit indicates viscosity when measured at 212 degrees.
Different types of engine oil are designed to work with specific engines. Conventional oil is typically the cheapest and is recommended for low-mileage engines once they have been broken in. A premium or synthetic-blend oil may prove a better choice for brand new engines and those that are placed under heavy load. Full-synthetic oils are formulated for use in high-tech and high-performance engines, and high-mileage oils make use of added seal conditioners to improve seal integrity.