Some say you should run one particular oil in 4 stroke mowers. Personally by the time a lot of mowers get their first oil change, anything is better than that thick black gluggy sooty Poo in the sump.
I generally use the left over oil from my cars oil changes, being either magnatec from Kirstins car or shell helix left over from the datsun.
Joe, during its working life oil gradually acquires suspended dirt, grit, and metal fragments. Oil filters limit the size of particle that is allowed to recirculate in the system, but four stroke mower engines seldom have filters. If you put oil that is already carrying a maximum load of suspended crud into a four stroke mower, you might as well leave the old oil in there. Perhaps the greatest benefit from changing oil in a mower is getting rid of the old load of suspended crud and starting off clean. (In a car engine the biggest benefit from changing oil is getting a new supply of detergents and other additives, but mower engines need new oil every 25 hours - cars engines, with their filters, mostly only need oil changes every 15,000 km). I think you'll get longer life from your mowers - many of them rare collectors' items - if you feed them new clean engine oil at regular intervals.
