Issue link: http://read.dmtmag.com/i/859318
Engine Oils Background & Properties castrol.com/GPS 800 255 4417 May 2025 GPS Industry Specifications Viscosity Index (VI) – A Measure of Performance Viscosity is one of the most important characteristics of an engine oil. By definition, viscosity is the measure of a lubricant's resistance to flow. Flow characteristics and temperature are directly related. For example, the higher the temperature, the more freely an oil flows; the lower the temperature, the more flow is inhibited. is relationship results in oil thinning as temperature increases and oil thickening as temperature decreases. VI and Temperature VI is a quick way to tell whether an engine oil can handle both extreme high and low operating and environmental temperatures. VI is the measure of change in an oil's viscosity relative to a change in temperature. Oils with high VIs (over 100) experience less change in viscosity relative to temperature. at means the oil guards against wear at higher temperatures and maintains pumpability and flow in low temperature environments. In multi-viscosity engine oils, VI is measured at 40°C and 100°C. ese oils present definite advantages to equipment performing in a wide range of temperatures. Blended with low-viscosity base stocks and enhanced with viscosity modifiers, multi-viscosity lubricants function in both high and low temperatures. e overall effect of a multi-viscosity oil is less viscosity change relative to temperature. For example, a 15W-40 translates to a 15 winter grade and 40 summer grade. High VI Benefits Maintenance managers choosing high VI, shear stable oils experience the following performance benefits: • Greater wear protection and oil film strength in high temperature and high stress environments, which equals longer component life. • Better cold startability and wear protection. Because the fluid remains viscous during low temperatures, oil reaches critical components quicker, limiting start-up wear. • Enhanced fuel economy and efficiency. All-around better flow characteristics at all temperature ranges leads to more efficient operations and greater productivity • Reduced oil consumption means less add-oil for operators. Not all viscosity modifier chemicals are created equal. e characteristics and qualities of base stocks and VI modifiers vary. It is critical that viscosity modifiers also promote good shear stability, or the oil's ability to stay in grade during use. For example, an SAE 15W-40 engine oil with VI 147, without good shear stability, may actually shear down to an SAE 15W-20 with a significant decrease in VI. A24 ecastrof