Originally Posted by LoneRanger
As an aside, yesterday evening I filled the F-150 with 89. Was indicating 1/4 tank, took 16.8 gallons. $6 more cost than to fill w/ 87. I swear the truck lost just an edge in throttle response, which is the opposite of what might be expected, although the small bump plus the ratio of remaining 87 to new 89 would only put the full tank at 88 which should make zero diff. Impulsive, idiotic thing to do actually. $6 wasted. This was an instant blend (for 89) station-- only three storage tanks, 87, 93, and diesel.
Well, believe it or not, when I switch from one brand to the next or if I've been running 87 and switch to 89 in the summer, I swear I can feel the car behave oddly on that first tankful. It seems to settle-out and return to normal after 50-75 miles or so. I don't know for sure but suspect the ECU is doing some adaptive learning.
Just recently however, a tank of mid grade from a brand new station that just opened up ran noticeably poorer for the whole tank. Weather, environment conditions and commute pattern remained the same. Quite certainly though, I could feel a distinct vibration in the steering wheel and gear selector lever. Things cleared-up about 50-75 miles into my next fill-up at one of my regular stations.
I always fill-up when the gauge gets to (or slightly below) 1/4 tank.
Ray