I use RTS, M1 0W-40, and Valvoline Premium Blue 15W-40 but will be switching to M1 15W-50EP GoldCap at the next OCI for all 4 cycle equipment. I keep spare a spare gallon or so of Premium Blue around in case I need a break-in oil for a newly rebuilt engine. For my father's riding mower that uses a spin-on filter, I use only M1 filters.