The names and characteristics of different base oils
Some of the first questions we encounter are about how to distinguish the names and characteristics of different base oils on the market.
To ensure that the performance of engine oil products will not be adversely affected when different base oils are used interchangeably, the American Petroleum Institute (API) divides base oils into five major categories.
Group I, II and III – all paraffinic base oils derived from crude oil; the sophistication of the process increases from Group I to Group II and then to Group III
Group III – also includes synthetic base oils, e.g., liquid hydrocarbons from gas-to-liquids (GTL), coal-to-liquids (CTL) or bio-to-liquids (BTL)
Group IV – specifically refers to polyalphaolefins (PAOs) synthesized from ethylene derivatives (olefins C8/C10/C12)
Group V – includes all other base oils, such as synthetic esters or polyalkylene glycols (PAGs) and naphthenes, which are obtained from naphthenic crude oils by conventional refining processes
Other names are used in the base oil market based on other characteristics, such as kinematic viscosity at 100°C (KV100), viscosity index (VI) and processing:
Kinematic viscosity at 100°C – can be used to distinguish between “light”, “heavy”, and “bright stock” and is associated with the base oil symbol. For example, PAO 4 refers to a Group IV light oil with a kinematic viscosity of 4 centistokes at 100°C
The meaning of SN - The symbol SN (neutral solvent) is used to distinguish Group I base oils based on the processing technology. For example, SN150 represents a Group I oil with a kinematic viscosity of 5 centistokes at 100°C
‘Synthetic’ Synthetic concept - used to distinguish synthetic base oils such as GTL or PAO
‘+’ - Recently, base oils with high VI outside the API definition range are marked with the “+” symbol. For example, Group II oil + means VI greater than 110, and Group III oil + means VI greater than 130
The key lubricity performance properties of base oils (such as oxidation resistance, volatility, friction and low temperature performance) improve as the grade increases from Group I to Group IV oils. The only exception is solvency, which decreases with the increase of saturated hydrocarbons.
