The API 1509 classification of base stocks used across the lubricant trade. Group I is solvent-refined mineral oil with under 90 percent saturates or over 0.03 percent sulfur; Group II is hydrotreated to at least 90 percent saturates with low sulfur; Group III is severely hydrocracked to a VI of 120 or more; Group IV is PAO; Group V is everything else, including esters, PAGs and naphthenics. Group number tracks purity and oxidation stability more than suitability for a given job.
Jug says full synthetic, but the base oil group on the data sheet is Group III, so it's hydrocracked mineral.
In North America a Group III oil can be sold as synthetic, so when a spec demands a true synthetic, ask for the base oil group in writing.
Also heard as
- API group
- Group I to V
Related terms
PAO
Polyalphaolefin, the synthetic hydrocarbon base oil built from alpha-olefins and classed as Group IV.
Ester
Synthetic or natural base oil made from acids and alcohols, valued for solvency, film strength and biodegradability.
PAG
Polyalkylene glycol, a synthetic base oil prized for low friction and clean running but hostile to most other oils.
Viscosity index
Number showing how little an oil's viscosity changes with temperature; higher means flatter.
Syn
Clipped shop word for synthetic oil or grease, as in syn gear oil or full syn.