Anyone have any suggestions as to that oil is best for use in an piston type air compressor. Been a while since it was changed.

30W non-detergent or if you can find it, a multi grade like 15W30 non-detergent. The same oil that should be used in most lawn mowers (and often isn't).

Detergent is added to oils to keep dirt etc in suspension and carry it to the filter. On non filtered systems like an air compressor you want any dirt to settle out and stay in the bottom of the crankcase. Non-detergent oils are used in these applications.

I use I-R synthetic compressor oil - don't recall the grade but it's the one they sell to honor their factory warranty. The cost is minuscule if it makes the compressor last some years longer.

Phillips MM 30 wt ( non det ) and an ounce of seafoam. 9 year old compressor. Was changed at 20 hour intervals for the first hundred hours and since is changed when it gets dirty ( through the sight glass ). DRAIN THE TANK DAILY if you are using it daily !

My Hitachi warranty requires synthetic oil,Great compressor, by the way!! :)

I also use the I-R synthetic oil. It's what the compressor came with so thats what I change it with.

The guy who sold me my compressor said to "Use any oil that says air compressor oil". That's a reminder, I need to change it again!

I also use Ingersall Rand synthetic oil.