I changed it out at the end of last season.
I was using Quaker State Synthetic 10w30, but I put in
15oz 15w40 Rotella, 1oz Marvel Mystrey Oil.
It smoked a bit at the initial seasonal start, only took 3 pulls, but soon afterward it stopped and ran normal.
I have had the mower for one season, a Toro with B&S engine, and after a couple hours of usage I plan on dumping the current mix and going to Rotella T6. At the end of last season I was still getting some silvery debires out with a hot oil change.