I have spoken to Representatives of Briggs, Kohler, and Kawasaki they are recomend NOT to use synthetic oil at all in their engines. First of all we as a dealership and the manufacturers recomend you DO NOT use Automotive Oil in their engines either - Automotive Oils today are formulated for newer engines and have about 20% detergents in them - causing foaming in small engines.... also we recomend to not only use small engine oil which doesn't have this detergent base but to us straight 30 weight during the warm months and only use 10W-30 if you are going to use the engine during the winter. Multigrade oils are actually the lighter number but act like the heavier weight number and burns off past the rings that is more than likely where you oil is going. We had a customer with a new Ferris ZTR and Kawaski motor - he owns a Kawasaki bike he bought at a dealer up the street and they were offering a double warranty for using the Synthetic Oil made for their bikes - he brought us the oil to use to service his unit and that is when we called the engine manufacturers.... Kawasaki explained it to us that their Synthetic was safe in the bikes because they achieve high speeds with enough air to keep the engines/oil cool and their small engines do not and the higher operating temps could cause the Synthetic to break down and burn off more excesively than conventional multi-grade oil... hope this makes sense..