Lube Condition Indicators
Viscosity index is the change in flow rate of a lubricant with respect to temperature. As a lube is heated it will get "thinner"; its viscosity will decrease. The amount of thinning which takes place over a given temperature span can be expressed as Viscosity Index (VI), a term expressed as a number without units. The less tendency a lube has to thin with temperature increase, the greater its VI. Determination of VI requires two viscosities at different temperatures (usually 40 degrees Centigrade and 100 degrees Centigrade).
Significance of viscosity: There are numerous references which cite that the viscosity of a lube is its most important single property, and perhaps this is true, at least When the lube is new. By itself however, a viscosity does, not nearly qualify a lube. It basically defines the film thickness the lube will have for a given application.
New lubes placed in engines, or other machinery should be inspected for correct initial viscosity. Assuming no errors are made with the initial fill, the following factors can influence viscosity:
Decreased Viscosity:
- Liquid fuel contamination
- Non-emulsified water contamination
- Shearing of VI-improving polymers
- Wrong make-up lube addition
Increased Viscosity:
- Solids contamination
- Certain emulsions with water
- Lube Oxidation/Degradation
- Wrong make-up lube addition
