You still have to dispose of the oil when you change it on a four stroke. How much of that oil gets disposed of properly? I have an Optimax 115. I have not seen one puff of smoke out of it when I crank it up. It is louder than the Mercury 60 hp four stroke I had on my 2006 boat but it is almost twice as large. My new Optimax 115 has a five year warranty also.