What is motor oil VI?
High or Low Viscosity Index ?
A lubricant may merit having a high VI for one or more of the following reasons:
- The optimum viscosity is not known
- Varying loads and speeds exist
- Varying ambient temperatures exist
- To boost energy efficiency
- To boost oil service life (lower average temperature)
- To boost machine service life (fewer repairs and downtime)
Cheaper, lower VI lubricants may make sense if
- Speeds and loads are constant
- Temperature is constant (constant ambient temperature or a heat exchanger is in use)
- The optimum viscosity at the operating temperature is known and is consistently achieved
An oil’s VI can also tell you useful information about a lubricant’s formulation, including the type and quality of base oils. For instance, highly refined and pure mineral oils will have correspondingly higher VIs. Certain additives, such as viscosity-index improvers and pour-point depressants, influence VI as well.