There are 5 base oils. Group I, I can't remember what it is, but I doubt any oil uses it today.
Group II is a refined mineral oil.
Group III is where the issues start. Everywhere in the world Group III base stocks are considered straight mineral oil base stocks. IIRC it was Castrol and Mobil that went at it in court. I think Castrol was pushing to get Group III reclassified as a synthetic and Mobil called BS on it. The "supreme" court decided that Group III base oils are synthetic. But they are not, nor do they behave like a synthetic.
Group IV base oils are polyalphaolefin (PAO's) and are synthetic base oils and are derived largely from methanol synthesis.
Group V base oils are essentially polyolester base oils and IIRC these are also synthesized from methanol or Methanol is used in the process.
Soooooo...what happens when you use Group IV or V base oils and try to use alcohol as a fuel, any alcohol that gets past the rings will actually behave as a solvent and it WILL start taking entire oil package apart.
I've seen it first hand. Oil pressure will go berserk and fluctuate. If you data log oil pressure you'd get an eyeful.
Then when you drain the oil, you will see the the oil coming apart. The polymer that is used to make the oil multi grade will seperate from the base oil. It looks like stringy liquid plastic. And that gets on the hot valve springs and other parts and makes a mess.
That is the short answer as to why you should never use Group IV or V base oils, or a combination of the two (really good oils use a blend of Group IV and V base oils to taylor the oil for whatever you need...that's why quality oils are 20 bucks or more a quart) with methanol.
