There's a lively discussion over on BobIsTheOilGuy about the benefits of 0W20 and similar 'fuel saving' oils. Has anyone here switched from a thicker oil (5/10W30/40) to a 'thin' (0/5W20) lube? Did you see a significant change in FE? Do you happen to have fuel log data? (Not a matter of trust, I'd just like to see the numbers! )