Technician a is correct that he says Oil is thickened by viscosity index improvers when it is hot and thinned when it is cold.
The viscosity index (VI) is an arbitrary, unitless measurement of how much a fluid's viscosity changes as a function of temperature. It is mostly used to describe the behavior of lubricating lubricants' viscosity-temperature relationship. The more the viscosity is impacted by temperature variations, the lower the VI. The viscosity index is a way to quantify how viscosity changes in response to temperature changes. The viscosity index, to put it simply, indicates how well a fluid can maintain its viscosity throughout temperature fluctuations. An arbitrary scale known as the viscosity index is used to assess how quickly viscosity changes as temperature rises. The rate of viscosity change as a result of temperature change is measured by a lubricant's viscosity index (VI).
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