Re: I gotta oil question too.........
Oil grouping is generally misunderstood because it is somewhat confusing. Oil groups do not define better-to-worse categories or types of processing or refining.<br /><br />Oil groups are based on interchangeability guidelines and determined by the base oil's sulfur content, saturates, and viscosity index. This is to ensure that the oil's performance is not adversely affected by substitution of one base oil for another (performance is actually tested on actual engines in a laboratory using ASTM standards). <br /><br />Group I base stocks contain less than 90% saturates and/or greater than .03% sulfur with a viscosity index greater or equal to 80 and less than 120.<br /><br />Group II base stocks contain greater than or equal to 90% saturates and/or less than or equal to .03% sulfur with a viscosity index greater or equal to 80 and less than 120.<br /><br />Group III base stocks contain greater than or equal to 90% saturates less than or equal to .03% sulfur with a viscosity index greater or equal to 120.<br /><br />Group IV base stocks are PAO (polyalphaolephins)<br /><br />Group V base stocks include all other base stocks not included in Groups I, II, III, and IV.<br /><br />"Synthetic" does not necessarily mean a Group IV polyalphaolephin or a Group V ester. Several years ago some PAO oil manufacturers tried to define that term with their oil in hopes of cornering the market. The courts decided not to have certain oil companies define what "synthetic oil" meant, particularly since many highly refined group III oils exhibited similar properties to PAO oils. This is why today we see some oils mixed with PAO's and some highly refined Group III's being called synthetic.<br /><br />One person might say that all motor oils are synthetic, because they are man-made from crude. Others might say synthetic oils are only those that do not come from petroleum, like some group V esters. Others would claim synthetics are those man-made from the refined ethylene (PAO). And still others would call synthetics highly refined Group III's. But unfortunately synthetic oils don't really have a definition or specification, particulary with regard to engine performance and ASTM standards.<br /><br />Most reputable oils today are of extremely high quality, exceeding the API and engine manufacturer's specifications. During the late 1990's and early 2000's refining processes allowed group III oils to nearly mirror the performance characteristics of synthetics. Consumers really benefit here because of the higher costs associated with PAO synthetics.
