Mileage Per Gallon

I know for sure we got some crappy lower octane than advertised (87) gas in the NC mountains, and when we had a really long hard pull on the interstate coming back, we got some wicked bad pinging for the two seconds it took me to shut the cruise control down when big Ex shifted to 3rd at 65mph. Next fill up we put in a higher octane (91), then got into the mountains again.. no pinging at what appeared to be the exact same conditions. (RPM incline, and road speed)

I don't think I have ever heard of damage from a higher octane being used, it just isn't always helpful or needed. Most modern vehicles will adjust ignition timing and spark to compensate anyways. Our GTi does that. It wants 93, but you can run it on 87.. and you can tell when you do. My guess is it cuts boost and timing advance pretty harshly, because merging and passing are noticeably different.

I was always under the impression that you can actually do damage to a car engine running higher octane fuel if not called for.  And could actually decrease your MPG using higher tyan recommended octane. 

Originally posted by David and Danette Originally posted by hogone Ethanol definately decreases MPG.  Another point that hasn't been brought up is time of year, use of air conditioner, windows up or down.  Probably minimal effect however.  And being a sailor I would like to add wind direction and speed.

Ethanol definately decreases MPG.  Another point that hasn't been brought up is time of year, use of air conditioner, windows up or down.  Probably minimal effect however. 

One variable that is difficult to pin down is the amount of ethanol that is actually in gasoline!
Ethanol may make gas burn cleaner but it has less energy per gallon.  Here in the Midwest, States are pushing for 15% ethanol vs the normal 10%.  Theoretically, this is a farmer pushed potential change.  More money for them but a noticeable decrease in mpg.  In Minnesota, several sampling tests were done and the 10% ethanol varied +/- 2%.  This may not seem to be much...but when
R-Pod owners are trying to 'hyper-mile' their tows, this can make a noticeable difference in mpg.
I took a trip out west with the Pod and as soon as I passed into another state which had non-ethanol 87 octane gas...my mpg jumped by more than 3 mpg!