I run cheap 10/30 and an oil conditioner like Lucas(start-up rattle is gone). But this engine has 200K on it. Runs very well for its age. The big deal is to change oil often, since the engine is not as well sealed or as tight on its tolerances as modern designs. A *lot* of grime gets sucked into it. Even at 3K miles, the oil is nearly twice as dirty as my dad's 10 year old Buick.
