My oil lube compressor recommends SAE 30 non-detergent oil. I broke in the motor/compressor with standard SAE 30 non detergent oil. I am now going to switch over to synthetic oil. Various reason, mainly cold climate. That's besides the point. My question is concerning ISO vs SAE ratings. Most charts show ISO 100 as equal to SAE 30. Also, ISO 46 as equal to SAE 20. But ISO 68 seems to get confusing. Some charts and oil manufacturers will list ISO 68 as equal to SAE 20; while some others will show ISO 68 equal to SAE 30. Obviously ISO 68 is thick; more viscous that ISO 46, so it's probably on the border between SAE 20 and SAE 30. Just like I saw some mention ISO 100 as equal to SAE 30/40. Obviously, ISO is on the high end of SAE 30 and lower end of SAE 40.

I am using an ISO 68 full synthetic oil. It's manufacturer even says this oil is intended for compressors who's manufacturer recommends SAE 30 non-detergent compressor oil. And being my temperature swing is drastic in winter vs summer, I'll probably change oil twice a year. Use the ISO 68 December through March and thicker ISO 100 SAE 30 April through November. My compressor only gets a couple of hours of runtime per week, so the oil changes are probably overkill. Money isn't the issue so I don't mind. Just curious if anyone had any definitive information on ISO 68 being acceptable for SAE 30 or is it too thin and I should jump to ISO 100 (SAE 30) full time? In the cold weather here I know the ISO 100 SAE 30 would probably put a big strain on the compressor starting up. Thoughts? Thanks. Mike