SOME crudes are better than Others for Lube Oil. One good example is Pennsylvanian crude Synthetic has many bases eg ESTER based. SOME synthetics way back didn't give much Protection from Oxidisation in 2 strokes and were avoided. Today SOME/Most syn and Mineral oils will mix so you can get Part synthetic and the syn is made from LPG. Most crude has a Lot of sulphur which is highly corrosive when oxidised and the Mixed with water. It has ALMOST been eliminated from the Best Oi/fuel countries, LPG also has impurities but is removed during the manufacturing process. Thickening oils is generally done by adding Polymers which are Plastic like Particles which have a finite Life in lube oils. It would be good if ALL engines were Pre-Pressurised with oil to reduce the damage of dry starts. Nev