84 vs 87 Octane and MPG

[desertland]

I've had my 01 Sport Trac for a week now and just ran out the first tank of 84 octane regular ( no 10% ethanol either ) and got 16.25 MPG. I read the manual and it recommends the 87 octane so my second fill up it with 87.
Just thought I would ask if anyone has noticed gains or losses depending on the fuel grade. I've heard some engines just do not care what you throw in it, you get the same MPG one way or the other.
If this has never been addressed ( some how I doubt that ) I'll post my results on the next fill up. My old Isuzu HATED 10% ethanol so it will be interesting to see.

 

[ncranchero]

I haven't seen any pumps labeled 84 Octane here??? Some 87's do say up to 10% ethanol.

 

[techieman33]

I haven't seen any pumps labeled 84 Octane here??? Some 87's do say up to 10% ethanol.

It's more common in higher elevation areas like colorado, I usually saw 85 out there. I think 84 will probably be fine, especially if your not agressive with the skinny pedal.

 

[John_Rock]

I always seemed to have heard pinging with 87, so for years I've been running 89 in my vehicles.