Last post on Aug 18, 2008 at 7:25 PM
You are in the Subaru Legacy & Outback
What is this discussion about?
Subaru Legacy, Subaru Outback, Fuel Efficiency (MPG), Sedan, Wagon
#29 of 49 Re: Subaru Outback 2008 MPG [pilot1226]
Jun 21, 2008 (3:25 am)
I just thought I'd also comment I don't condone everyone running out and buying premium fuel - the octane rating is simply the fuel's resistances to detonation (premature ignition). Higher-end cars that call for premium gasoline have a higher compression ratio in the combustion chamber (the specific ratio is typically found under the performance specs of the car), so the fuel needs to resist spontaneously combusting when it enters the chamber.
I would keep in mind too that you could - keyword COULD - run into fuel injector issues if you continuously run 93+ octane in a car that says "Unleaded 87 or better". I usually run plus test when I have long road trips, and a tank of premium every few months.
If you want more information on why not to run premium constantly in a car built for 87 octane, Google it. There's a lot of returns.
#30 of 49 Re: 2007 2.5 base automatic, 34 mpg. [peralta]
Jun 24, 2008 (7:54 am)
While we're all talking about MPG's, I figured I have a deep thought for us to discuss:
Gasoline is sold by volume (gallons in the USA). Temperature is directly proportional to density (If you have thing "x" at two temperatures, one higher and one lower, the lower temperature one is more dense.)
My thought is, if you purchase gasoline in the early morning hours before the sun rises and starts re-heating the earth, you're getting more gasoline than when you purchase it in the middle of the afternoon. While the volume is the same, the density is different, and in theory you should be able to get better mileage out of the tank that was filled in the early morning.
#31 of 49 Re: 2007 2.5 base automatic, 34 mpg. [pilot1226]
Jun 24, 2008 (7:59 am)
There was a news report on this recently, but I unfortunately don't remember the news source. The bottom line, however, is that whatever gain you get is really minimal and not worth the effort.
#32 of 49 Re: 2007 2.5 base automatic, 34 mpg. [pilot1226]
Jun 24, 2008 (2:06 pm)
The tanks are underground and well insulated from temperature fluctuations.
Jun 25, 2008 (12:29 pm)
lower octane fuel doesn't give as much energy per joule compared to plus or premium.
isn't a joule a joule regardless of its anti knock capability????
#34 of 49 Re: joules [cptplt]
Jun 25, 2008 (6:18 pm)
Yes and no. Since there's more resistance to premature detonation, there's more power in the bonds of the hydrocarbon, therefore it releases more energy when the bonds are broken.
It's a minimal gain.
#35 of 49 Re: joules [pilot1226]
Jun 27, 2008 (2:11 am)
Actually from what I remember if your car is tuned to run on regular you will actually get MORE power from a lower octane fuel than from a higher octane fuel. The higher octane is merely there to prevent detonation before the spark plug detonates the fuel due to heat.
Bottom line is unless your car is tuned for premium (turbo cars/supercharged cars, higher performance cars) then you are wasting your $ on premium.
#36 of 49 2008 Outback 2.5i Manual
Jul 06, 2008 (11:25 pm)
I live in Los Angeles and my one-way commute to work is about 13 miles hwy. Round trip, the dash computer says 28.5ish mpg. On a recent 60 mile roundtrip this weekend, trip computer noted 33.6 mpg.
I drive like a grandma (no offense), between 58-63 mpg. I use the cruise control when possible and avoid all the jackrabbit starts at the line. Car only has about 3500 miles on it now, would like to see how mileage changes as we head to our camping spots in the mountains this fall.
#37 of 49 Re: 2008 Outback 2.5i Manual [carlo808]
Jul 07, 2008 (10:01 am)
Grandmothers should not be offended, in fact with current gas prices they should be proud! 33.6 mpg sounds good to me!
#38 of 49 Re: 2008 Outback 2.5i Manual [ateixeira]
Jul 08, 2008 (7:51 pm)
I've seen grandmothers driving STis before.