Here's another anecdote. I've added another cell to my
 spreadsheet to calculate the separate average since the gas I use
 started adding 10% ethanol in August of 2009.  Haven't really
 noticed much of a difference in the averages (19.28 before the
 ethanol date, 19.01 after that date, and 19.25 overall including
 all tankfuls since I bought the car). Those numbers pretty much
 reflect my overall driving habits and destinations.

 Harley

 Well I am fond of the OBD II method  because it indirectly reveals
 the BSFC. Drag and therefore HP required is constant. It would not
 surprise me to find out the trailing plugs hurt the mileage as they
 are there mostly for smog reasons.

 Lets see 19.01/19.28 = 9.8% hmmmm 10% ethanol you say :)

 Paul Lamar

Oops, math class.

(19.01/19.28)100 = 98.599%.  100 - 98.6 = 1.4%. Now 10% ethanol will not
affect milage by 10%. It will reduce it due to the lower BTU content.

Dale Davies

John beat you to it :)

Paul Lamar


Just a comment on ethanol (which I prefer to call crapenol!  It's
only purpose is to enrich corn and sugar cane growers.  When you
calculate the oil used to fuel the tractors, manufacture the
fertilizers and ferment and DISTILL the stuff, you would use fewer
barrels of oil if you just made it into petrol or diesel
fuel.  Numbers I have heard range from 1.2 to 1.5 gallons of
petroleum consumed per gallon of crapenol produced.  And the crapenol
has less energy content than a petroleum fuel.)

My street car is a 2005 Buick with that very well developed 3.8
V-6.  Before FL started putting 10% crapenol in the gas, I got 29-30
MPG on the highway.  With the crapenol, I see maybe 25-26 MPG.  This
seems to be independent of seasons.  I have seen the MPG go back up
when I encounter crapenol free gas when traveling out of state.

SD
Orlando, FL