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Base oils made by hydrocracking and isomerization technologies had such a signifigant increase in desirable performance over solvent refining technology that in 1993 the API categorized base oils by composition. Solvent refined oils are now referred to as group I base oils.
Group II base oils are a vast improvement over group I because they contain lower levels of impurities and because they are so pure, they have almost no color at all.
Improved purity means the base oil and additives can last longer under use. The oil is more inert and forms less oxidation byproducts that can increase viscosity and react with additives.
Group II Base Oils over Group I Base Oils offer:
Better Thermal stability, Better Oxidation stability, Longer service life, Increased component protection, Better resistance to the formation of Laquers and Sludge
