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1. A measure of internal resistance to flow.
2. Viscosity of an oil changes with temperature, falling when temperature rises and vice versa.
3. For crankcase oil, viscosity is between 130 – 240 Sec. Redwood No. 1 at 60°C.
4. For cylinder oil, viscosity is 12.5 – 22 Cst.
Viscosity Index, VI:
1. The rate of change of viscosity of an oil, in relation to change of temperature.
2. Oil of low VI has greater change of viscosity with change in temperature,
than the oil of high VI.
3. For crankcase oil, VI is between 75 – 85; For cylinder oil, VI is 85.
4. Highest VI of mineral oils is about 115 and with special additives, this may be raised to about 160.
5. Hydraulic oils, used in remote control hydraulic circuits must have very high VI; otherwise erratic response to the controls can be troublesome. (Telemotor hydraulic system oil has VI of 110.)