I have been told the air cooled engines are about the hardest on motor oils that you can throw at them. On that same subject,I was useing my Cub Cadet "2145" hydro (14 HP single Onan) quite hard today,and stopped to get a cold drink,Meanwhile I took my hand held infra temp gun and shot around my hot engine,WOW the sump was well over 300 degrees! with the oil filter itself at 303 degrees!!! I use this mower very hard,but really it is real dependable.I run Mobil 1(15W-50)I would say this temp. would break down a non syn. oil very quickly. what are your thoughts? Gregg/Ohio