I have used synthetic several times over the years and have not noticed any difference at all in performance or fuel mileage. I have Amsoil synthetic in my Duramax diesel now and not even a tenth of a mile per gallon increase in mileage or performance, but with a diesel I am going to use it in the winter for easier starts and less engine wear in hopes to not ever have an engine overhaul. In moderate temps I think it's a waste of money. This is why I think it is a waste. I just got rid of my 96 f-150 4.9 6 cyl., I parked it outside since it was almost new 24k mi. I used whatever oil was on sale and changed the oil and filter about every 6,000 miles until 180,000 miles and then every 10,000 miles until I junked it at 225,400 miles. The engine ran as good as new and the last days burned a quart of oil every 5,000 miles. The truck before that was an 86 Ford 150 4.9 6 cyl., bought new , parked outside it's whole life till I sold it at 213k . I ran synthetic once when it was new and then whatever oil was on sale. I averaged an oil and filter change every 4,300 miles through the life of the truck. At the end it burned a quart of oil about every 1,000 miles. I ran these motors hard too because the power just ain't there. So how can synthetic be so much better? Both the trucks were junk in almost everyway except the engine so the oil did it's job. I am sure I could have ran the 96 engine to 300k mi.