Engine....also how often on air filter change? Dino or Synthetic? First oil change in 3 years, which I know is BAD.
I have a Yth24v48, and it's doing fine, so far. I use Pennzoil 10w30 and change it, and the oil filter every 50 hours....about once a year. In the Winter, when it sits for a long time, I fire it up and run it for 20 or 30 minutes, until the engine reaches a good operating temperature....which also helps keep the carb from gumming up. Every 2 or 3 cuttings, I clean the air filter....wash the foam "pre filter", and vacuum any dust/dirt off the filter, and the inside of the filter housing....if I mow on a dry day, and kick up a lot of dust, I clean the filter afterwards. IMO, any good quality oil is ok, so long as you follow the owners manual recommendations....and I prefer the 10w30 over a straight weight. Leaving the same oil/filter in for an extended period of time...3 years...can allow moisture to build up in the engine, and cause premature wear.