Notice that they don't compare synthetic against conventional oil when determining whether a energy conserving formula is granted. The compare the synthetic against the reference synthetic.
The additives in conventional break down very quickly. Synthetic oil uses much fewer additives because of the nature of its far superior base stock. I will bet that any tests between synthetic and conventional oil conducted at
2500 miles with the same oil would yield even bigger differences.Notice that when comparing two conventional oils (5W-30 and 5W-20) Ford found .6% difference in fuel economy. So you say there cannot be a 1.0 % difference between synthetic and conventional oil?
The Southwest Research Institute you provided a link for used a 1993
4.6-liter Ford modular V-8 engine. I am sorry but I would not accept any results from an engine design that old, and further I personally would not accept any results from a US manufacturer's engine, whose build tolerances are not the same as Toyotas and Hondas. If you have a Ford engine, go ahead and use recycled conventional oil, because it will not make any difference.Let me ask you a question. Have you ever changed to synthetic oil in a relatively new car (after about 5K - 10K miles) and observed the difference? I have, and it is instantly noticeable.