I doubt there are ANY Group I base stocks in SL rated oils*. I wouldn't be surprised if that was also true of SJ oils, too. (I know well before the SL oils were intro'd, Equilon Havoline expounded on the back of the bottles about their use of Group IIs in their SJ products.)
There is NOTHING about Group I base stocks you want in your car's engine if you can avoid it. It's undergone only a minimum of hydro-processing, and still contains unstable aromatics that evaporate off and also oxidize readily, as well as sulfated hydrocarbons that promote acid build up as they in turn are oxidized. In the end all this sets the stage for consumption, corrosion, and sludge. Both these nasties are left only in trace amounts in Group II base stocks (as in single digit parts per million amounts). A good deal of the residual waxes present in Group I base stocks are elliminated by hydro-isomerization into desirable paraffinic lube molecules in Group II base stocks, too. THAT translates to a desirable higher viscosity index.
*Not counting the possibility that the additive carrier might be Group I base stock.
[ October 06, 2003, 12:53 PM: Message edited by: Ray H ]
