I have posted about different groups of oil bases a few times so I will give a better explanation below of the bases.
Lubricant base stocks are categorized into five groups by the API.
Group I base stocks are composed of
fractionally distilled petroleum which is further refined with solvent extraction processes to improve certain properties such as oxidation resistance and to remove wax.
Group II base stocks are composed of
fractionally distilled petroleum that has been
hydrocracked to further refine and purify it.
Group III base stocks have similar characteristics to Group II base stocks, except that Group III base stocks have higher viscosity indexes. Group III base stocks are produced by further hydrocracking of Group II base stocks, or of hydroisomerized slack wax, (a byproduct of the dewaxing process).
Group IV base stock are
polyalphaolefins (PAOs). A synthetic.
Group V is a catch all group for any other synthetic and mineral base stocks. Examples of group V base stocks include
polyol esters,
polyalkylene glycols (PAG oils), and
perfluoropolyalkylethers (PFPAEs).
Groups I, II, and III are sometimes referred to as
mineral oils and groups IV and V as
synthetic oils. However, most manufacturers have labeled their group III based oils as synthetic in the US for reasons of economy and marketing.
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