It depends on many factors, piston vs. scroll/rotary, splash vs. pressure/filter lubrication, ambient temperature/humidity, run time, etc. A standard reciprocating using mineral oil, the typical change interval oil is around 200 hours. Switch that to a full synthetic and the interval is in the range of 2,000 hours. A scroll is around 8,000 hours with synthetic. If you put on low hours per year, then standard mineral oil is fine, and the factor of oil changes is more because of water in the oil as opposed to the oil wearing out. If you are using your compressor frequently with longer run times, then synthetic would be the way to go. If you operate the compressor at temperature extremes, a synthetic would be a better choice. In either case I would change the oil at least annually. I have a dual stage rotary compressor which gets infrequent use I Mobil Rarus 427, Compressor, 1 qt., ISO100, SAE Grade 3, it is 2 qts per oil change. A synthetic would be a waste of money, as I would still need to change the oil annually. I did put an hour meter on my compressor, the actual tun time is a lot less than one thinks. I primarily use Mobil and Miles oils, the latter usually in a 5 gal pail for my other machines. Typically use Zoro for the free shipping. Also note that some compressor manufactures will only extend their warranties if you buy their oil kit. Manuals indicate oil recommendations and frequency, I usually stick with mainstream manufactures as the cost difference is small at the quantity that I use.
