Engines require oil to create a protective lubricating film between moving metal parts, preventing friction and wear. Oil also helps carry heat away from critical components, contributing to overall engine cooling. In addition, it suspends and transports contaminants to the oil filter, keeping internal passages clean. Without proper lubrication and heat control, engine components would quickly overheat, seize, or suffer catastrophic damage.
Oil viscosity refers to the thickness of the oil—how easily it flows—and lower numbers indicate a thinner, less viscous oil, meaning 10 is less viscous than 20. Modern ratings like 0W-20 come from the SAE scale, where the “0W” reflects how easily the oil flows in cold temperatures (the “W” stands for winter). The “20” indicates the oil’s viscosity at normal operating temperature, with higher numbers providing a thicker protective film. Automakers increasingly specify 0W-20 to improve fuel economy and reduce emissions, but its thinner nature has sparked debate among technicians about long-term engine protection.
Conventional oil is refined directly from crude petroleum, while synthetic oil is chemically engineered to have more uniform, stable molecules. Because of this engineered structure, synthetic oil maintains its viscosity better across extreme temperatures and resists breakdown longer than conventional oil. It also provides improved lubrication, reduced engine deposits, and superior protection under high-stress conditions. Although synthetic oil costs more, many drivers and manufacturers prefer it for extended drain intervals and enhanced engine longevity.
Oil manufacturers create different viscosities by blending base oils with carefully engineered additive packages that control how the oil behaves at various temperatures. Viscosity-index improvers help the oil remain thin enough for cold starts while still maintaining adequate thickness at high operating temperatures. Detergents, anti-wear agents, and friction modifiers further influence how the oil performs and protects engine components. By adjusting the ratios and types of these additives, manufacturers can produce oils that meet specific SAE viscosity grades such as 0W-20, 5W-30, or 10W-40.