Ok you say if you run regular change your oil every 50hrs and if you run synthetic you can change it every 100hrs. To me that sounds stupid and the reason being is that the synthetic is going to be just as dirty at 50hrs as the regular oil is in a mower. Oil change intervals can be as short as 3,000 miles or as long as 15,000 miles on some new cars. Even the oil manufacturers recommend that you follow the oil and filter change frequencies shown in your owner's manual. So you should also do in your mower manual.