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Big Daddy 06-20-2011 06:11 PM

Interesting Gas Mileage Change
I've been running the 93 octane tune in my truck and consistently getting around 20.3 mpg on the highway running about 65 mph. While on the Gatty trip the best gas I could find in TN was 92 octane (they may sell higher but that was the best I could find) so I had to run that and because I left the Diablo at home I couldn't de-tune the setting. After running two tanks through on our trip my highway mileage dropped to 18.4 mph, down roughly 11.1%, on the trip back home. All of this mileage was noted using the on-board computer so even if not completely accurate I was comparing apples to apples. I didn't notice any knocking or pinging going on with the lower octane but there definitely was a decrease in mileage. Do you all think a drop of 1 octane could cause that or do you have some ideas of what's happened? Oh, and we didn't come home with a bunch of souvenirs so no weight difference on the return trip.

theweavman 06-20-2011 06:24 PM

I mentioned this on another recent blog, Gasoline is blended differently in different states and different regions of the same state... No mater what brand name is on the pump, all the gasoline comes from the same area refinery...meaning the gas being pumped at a Chevron, or Mobil, or Arco or Texaco, or Shell, in the same town, most likely all came from the same place, and possibly from the same tanker truck.... So, your gas mileage variance, may be more dependant on the refinery and the local blending than on the octane markings your seeing on your pump....There is so much BS in the world today, it's tough to believe in almost anything, sometimes left over gas in trucks, is sold at a discount to stations just to get rid of it, and who knows what the station owners are told?

MADDOG 06-20-2011 06:30 PM

You may have gotten some leftover winter blend fuel, Dennis!

Either that or you've somehow increased the frontal area of your Ram... ;)

Big Daddy 06-22-2011 06:47 PM

Got to thinking more about this and I'll bet I just got some cheap blend gas. Other than the National Park the Gatlinburg/Pigeon Forge area is just one vast tourist trap and I can believe every station on the main drag buying the cheapest stuff they can to rake in more from the tourists. Next year I'll get a little off the beaten (tourist) path to gas up.

kewlguy53403 06-22-2011 07:48 PM

Could the overall grade of your drive have affected the milage as well?

Big Daddy 06-24-2011 09:13 PM


Originally Posted by kewlguy53403 (Post 553992)
Could the overall grade of your drive have affected the milage as well?

Don't think so. Birmingham is roughly 600 ft above sea level and Gatlinburg comes in around 1300 ft. Looking at the big scheme of things I was going uphill to the mountains when I got the best mileage. Pretty sure it was the gas.

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