Measurements were carried out at constant shear stress 7. (given on curves) on viscosity of a crude oil with 25 wax. So we always advice to take preventive action rather than run to fail (RTF) mode. Kinematic viscosity is defined as the quotient of the dynamic viscosity and the density. The CCS viscosity test evaluates the amount of energy it takes to start an engine at a. The lower the W rating, the faster the oil flows when cold and the easier it is for the engine to turn over when starting. Once the oil degrades to a large extent, the VI comes down and it damages permanently. Dynamic viscosity determines an oil’s low-temperature, winter or W viscosity rating the 5W in 5W-30 motor oil. Now to conclude, Viscosity will remain good only if we maintain the oil properties within the limits. Greater mechanical friction may happen at too low viscosities, resulting in higher loads and more wear and tear in machines. For example, some oils may become very thin and lose their lubricating properties at high temperature, while others may maintain their viscosity and lubricating properties even at high temperatures.įor instance, excessive viscosity may cause poor oil flow, which in turn leads to oil starvation and dry startups. Take, for example, this comparison of two common substances with different viscosities: water and honey. In a nutshell, the thicker the fluid is, the more resistance to flow it will demonstrate. However, we should also note that, different oils have different rates of change in viscosity with respect to temperature. More precisely, viscosity is the measure of a fluid's resistance to flow (under certain conditions). Viscosity of an oil decreases as the temperature increases, which means that the oil becomes thinner and less viscous. Oils with a low viscosity index will have a high change rate in viscosity with respect to temperature, meaning they will become less effective as lubricants at higher temperatures. Oils with high viscosity Index will have a low change rate with respect to temperature, i.e, they will maintain their viscosity and lubricating properties over a wide range of temperatures. 120, whereas, the synthetic based oils have a VI of nearly 250. High- quality mineral oil has a VI of approx. The temperature used for measuring the viscosity is 40℃ and 100℃. In this process, the reference oil used is typically a high-quality oil that has a very low rate of change in viscosity with regards to temperature. It is calculated by comparing the change in viscosity of an oil with temperature to the change in viscosity of a reference oil with the same temperature change. Viscosity Index (VI) is a measure of the rate of change of a unit of viscosity with respect to temperature. Viscosity Index (VI) is an important property of lubricating oils as it indicates how well the oil will maintain its viscosity over a wide range of temperatures.
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