Regarding Group II. Let us not forget that the original purpose of the Hydrocracking process was to enable refineries to process low quality crude and get sufficient recovery to make processing them economically feasible. It was NOT to just make better base oils.
The folks who had access to high quality crude had no reason to switch to Hydro processing as solvent refining techniques already yielded very high quality base oils with good recoveries.
That said, there are some good characteristics of Group I oils that can compliment the deficiencies of Group II oils. Yes, Group II's, III', have some deficiencies as engine oil lubricants. Just as Group IV (Pao's ) are supplemented with Group V oils (Ester), Mobil's Delvac 1300S as example, is actually a blend of Group II+ and Group I base stocks to fulfill very much the same properties as the PAO/Ester blend in full synthetic engine oil. Group II is extremely stable and as such can have additization suspension/fallout problems and does not have as high a natural detergency level as Group I oils. Group I has excellent natural detergency (like esters) and good additive solubility.. Thus by combining the two in the right proportion, one can achieve an oil with excellent additization hold, excellent cleanliness and all the advantages that Group II+ can yield. Your basic synergism.. Again, very much the same as synthetics are with their combination of PAO and Ester.
Why doesn't everyone do it? Some companies do not have the capabilities to use both base stocks and only have one or the other product produced in house.. And then again there really are differences in oils, different manufacturing philosophies, different qualitiy levels, different applications. It is what makes oil so interesting and fun!
George
[ August 08, 2002, 09:43 PM: Message edited by: GeorgeCLS ]
