After reading all the answers and you still cant figure it out. Dont change it. Its simple. Then wonder for the next few years what damage you may or may not have caused. Wasting resources? Oh Christ. Now you're a freakin tree hugger. Why use a gas powered mower and pollute the air in the first place? Got get one of the old mechanical push lawnmowers. There, feel better? Saving a $2 quart of oil or spending $300, $500 or $1000 for a new mower just because you wanted to save some oil. Senseless boy, Senseless! Bubba