What are the different kinds of base oils?
Base oils are be classified by both viscosity and their generic chemical composition, itself a function of the original crude oil and/or the refining process. Depending on the proportions of hydrocarbon molecule type: base oils can be either paraffinic, naphthenic or aromatic in nature. There are several widely used viscosity classifications, of which the term ‘solvent neutral’ is the most common, e.g. SN 150 and SN 500, where the number represents the SUS viscosity (measured in Saybolt Universal Seconds at 40 C). Base oils are also classified by their viscosity index (a calculated figure based on the viscosities measured at both 40 and 100 C). Thus oils are either Low Viscosity Index (LVIs) or Medium Viscosity Index (MVIs), High Viscosity Index (HVIs) or extra High Viscosity Index (XHVIs). The higher the viscosity index, the less the oil will ‘thin down’ upon heating, and the less it will ‘thicken up’ upon cooling. Base oils are also be defined by the type of refining process used: so
