I ran premium until about a month ago when I switched over to 87 with no noticeable difference in mileage. I'm still training myself to drive conservatively. Old driving habits are very hard to break. I need to get a ScangageII for some real time feedback.
The issue is NOT gas mileage it is engine damage. Predetonation to be exact. If you run the motor under low loads on a cool day you should not have a problem. Under high loads and hotter days the motor may predetonate thus igniting the fuel on the up stroke of the piston too early and cause engine damage. That being said our engines do have knock sensors that will retard the ignition to resolve this condition somewhat. If you are running lower octane and hear some engine knock think of changing to a higher octane. Unfortunitly in our engines we may not be able to hear the knock before the knock sensors retard the ignition. Bottom line is that it may be OK to run lower octane but as a rule if I am going to ask the engine to do any type of hard work such as trailering and offroading or on hot days I will increase the octane to head off any predetonatiion and possible engine damage.
Believe it or not, as of a couple of days ago, there were still 2 places (across the street from each other) that are charging "just" $3.99/gallon for regular in San Francisco, which just got displaced as the MOST expensive place in the country to buy gas by Chicago.Have been running 87 for a while. Now every gas station around me is at least $4.07 for 87