1985 Craftman tractor 16HP B&S eingine, 4 hours a week cutting 2 acres during the summer then used a bunch of times during the winter for snow blowing. Every year change the Pennzoil 30WT, new air filter, fuel filter and spark plugs, that's it. It sits out in the shed all year and it runs like a top, smooth, no smoke, starts EVERYTIME. Running a synthetic motor oil a lawn mower and then changing more that once a year really is a waste and not enviromentally friendly.