ISO VG 680 gear oils

ISO VG 680 gear oils collects 23 oils from Castrol, Chevron, Mobil, Shell in this catalogue. The ISO viscosity grade is the oil's thickness at 40 °C, plus or minus 10 percent. Match the grade the machine manual names before you compare brands. The figures below are the makers' typical values, not a batch certificate. Confirm the current data sheet before you fill a machine. Published viscosity indexes run from 83 to 265. A higher index thins less between 40 °C and 100 °C. That matters in a cold start and in a hot gearbox, and it is not the same thing as the ISO grade. Pour points run from -45 °C to -6 °C. The machine should still start at least 5 °C warmer than the pour point of the oil you pick. 12 are flagged synthetic and 11 are not. Synthetic here means the maker said so. It is not a viscosity grade and it is not, by itself, a reason to leave the ISO grade the manual asks for. 2 of these oils are PAG (polyalkylene glycol). PAG does not mix with mineral oil or PAO. Drain and flush before a change into or out of a PAG, and do not treat a PAG as an equivalent of either. 2 can be bought in a small package from the retailers linked on each oil page. The others have no listing yet. A missing buy button is not a comment on the oil. Use the table to sort the grade, the viscosity index and the pour point, then open an oil for its data sheet, its equivalents and its buy links. Equivalents on this site are other published oils in the same application and grade. They are not exact substitutes, and the OEM specification still governs.