simple explanaton ofgoil groups

Originally posted by edwardh1: Is there a SIMPLE explanation of what the oil groups are, AND what oils are in what group anywhere? I looked.
Keep in mind that the "groups" only refer to the BASE OIL that serves as the foundation of a finished motor oil. The more you read on this board, the more you'll come to know which finished motor oils are built on which groups. As for an explanation of what these groups are, this is as simple as it gets: Group I = refined crude, with the wax removed by solvent treating and SOME of the impurities removed through hydrogen finishing. Group II and II+ = refined crude, with the wax CONVERTED to "oil molecules" by isomerization, and the impurities removed or converted by "cracking" their molecular structure. Group III = same as above, but with more of the wax converted and more of the impurities cracked. SOME Group III base oils are pure wax isomerates, meaning they are made FROM the wax removed while making a Group I oil. Typically these type Group III oils have much less impurities than other Group IIIs, as well as much higher VIs (viscosity indexes). Group IV = synthetic hydrocarbons known as Polyalphaolefins or PAO. This is the primary element of the base oil blends used in Mobil 1 and Amsoil. Group V = all oils not included in the other groups. For motor oils, this is primarily esters, which in some synthetics make up 50% or more of the base oil blend (along with Group III or Group IV), but in most synthetics oils that contain esters, there is more Group IV.