I have a 2007 ST with 93,000 miles .I am currently using a full synthetic oil . Sometimes when I first start the engine a puff of smoke comes from the tail pipe . It may happen twice in a week or once in a month . That Is the only time I see smoke .Its not a lot of smoke just a puff then it goes away and no more . It is not using oil . Usually thats a sign of valve seals leaking a little but it does not do it often . Anyone have this same experience ?