Compressor oil does three jobs: it lubricates, it cools and it seals the airend. The choice between mineral and synthetic oil affects service intervals, deposit formation and how the machine handles high temperatures.
Mineral oils
Mineral oils are lower cost and suit older machines and moderate-duty applications. They oxidise faster at high temperature and need more frequent changes, but in light-duty service they are adequate and economical.
Synthetic oils
Synthetic oils resist oxidation and thermal breakdown, extending service intervals often to 6000–8000 hours or more. They flow better at low temperature, control deposits and keep the airend cleaner, which makes them the standard choice for continuous and high-temperature duty.
Choosing the right oil
Follow the manufacturer specification rather than mixing brands or grades. The wrong oil can cause varnish, increased carryover and shortened airend life. Changing from mineral to synthetic is possible on many machines, but only with the maker approval and a full flush.