Yes, as
'Kule and a couple others have pointed out, the typical lawn mower engine (B&S, Honda, etc ...) are very robust lil' beasties. Any oil, with years in between oil changes, will do. Just about every other part of the machine (lawn mower, generator, pump, etc ...) will wear out, rust out or otherwise fail before the internal combustion engine does.
So, any time spent agonizing over choice of oils is time wasted for nothing.
Of course, I'm the worst offender in this regard.
I get off on babying my stuff so I'm another clown looking for that "perfect" lube.
I use the 15W40 fleet oils, namely; Chevron Delo400, Pennzoil Long Life and Schaeffer Supreme 7000 (synthetic blend). Their robust additive package is more than capable of surviving the more common torture tests we subject out equipment to.
As for a straight weight oil, I'd use either Pennzoil (30 and 40 weights are both available at WalMart) or Chevron Del400 in straight 30 which i think you can get at AutoZone. The Pennzoil has a group II+ base oil plus moly and the Chevron oils consistently turn in great wear results in the UOA section of this forum.
I have been less than impressed with OEM brand oils, in general. They seem to be of indifferent quality.
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Bror Jace