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Subaru Forester MPG-Real World Numbers

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Comments

  • cinemod1cinemod1 Posts: 1
    Never did better than 21mpg, whether I go 65 or continuous 85mph.
    - 80 miles per day 95% highway.
    - - Use 87 octane, with that lousy ethanol.
    - - Tried all brands of gas - no difference.

    Tried Octane booster to a tank of gas, new special, copper plugs - drove 65-70mph - 20 mpg.

    Winter milage is even worse.
    My '92 Legacy LS Wagon got 25 and it's >= 400 lbs heavier.
    ( It's still on the road BTW )

    How are you achieving those type of numbers?
    Dom
  • subearusubearu Posts: 3,613
    Both of my Subies were not driven lightly, I would allow it to rev into the 3-4k rpm range normally and even higher when necessary. Doesn't require a lead foot to do that either. I do run Mobil-1 in my cars though, which may help 1mpg or so.

    -Brian
  • joseph50joseph50 Posts: 235
    Just for the heck of it, during a day on the turnpike I was curious to see what it cost to run the AC. (2001 Forester S, AT.)
    Filled up, then took it down to exactly the first quarter tank mark. 108 miles without AC.(It was just cool enough to run with windows closed.)
    Upon next fill up, I did it again, but ran the AC on number 2 setting. 86 miles to the quarter mark. Pretty significant, I say.
    Joe
  • ateixeiraateixeira Posts: 72,587
    The fuel guage isn't really that precise, I doubt the actual different is that pronounced.

    Try a full tank, and even then, just one tank isn't really significant.

    I track my mileage, and I've found that in the summer my average dips about 1 mpg, likely due to the A/C. But...in the winter, my average dips about 2mpg, due to having to warm it up longer is my guess. So the A/C puts less of a burden overall than having to warm up from freezing temps.

    -juice
  • gouldngouldn Posts: 213
    I've had my 01 Forester (S+ Automatic) for 102K now, and am getting 24 MPG.

    I did notice that mileage improve markedly after ~7500 miles or so.
  • growler5growler5 Posts: 67
    How are you achieving those type of numbers?

    Not by driving 85mph. Speed kills gas mileage. The sweet spot seems to be about 45-55 MPH for most cars.

    The FXS isn't going to win any prizes for minimum air resistance either.

    It's too bad the EPA doesn't do an experiment with the MPG test by doing the standard test for highway speed, and then repeating the test at a higher speed, say 80-85 mpg. It would be interesting indeed to see the MPG difference.
  • jim314jim314 Posts: 491
    The EPA test wouldn't allow a comparison of the difference in fuel use between moderate and high highway speeds because the EPA test is done on a dynamometer with the vehicle stationary relative to the air. The air resistance is accounted for by a calculated correction.

    The air resistance is proportional to the speed cubed so it rises strongly with increasing speed. But this doesn't mean that the proportionality factor is 1. Link.
  • tidestertidester Posts: 10,110
    The air resistance is proportional to the speed cubed ...

    That's actually the power required to balance the force of air drag - which varies as the square of the speed.

    tidester, host
  • jim314jim314 Posts: 491
    Thanks for the correction.

    That third power bothered me, but I didn't think it out. In the past the usual reference has been to the retarding "force" of air resistance, which for simple physics problems I thought was proportional to speed, so power (speed times retarding force)should be proportional to the second power of speed. But in air, and with turbulence, etc. the retarding force must be proportional to the square of the speed in order to give a third power dependence of the power. As I recall the old statement was that the "air resistance" at 70 mph was twice that at 50 mph, which fits with the force being proportional to the square of the speed since (70/50)^2 = 1.4^2 = 2.0.

    The power (metric unit of power is the Watt, where 1000 W = 1 kW = 1.34 HP) is the energy consumed per unit time, but what we usually want to know is energy consumed per unit distance travelled. In Europe this is the litres of fuel consumed per 100 km travelled, but in the US we use the reciprocal, that is, distance travelled per unit of fuel consumed (mi/galUS or simply "mpg"). FYI the conversion between the European and US measures of fuel economy is y mpgUS is related to the equivalent z L/100km by yz = 235. That is, you divide whichever one you have into 235 to get the other one.

    But the point is that to get the extra vol of fuel consumed per unit of distance caused by driving faster we should divide the vol of fuel consumed per unit time by the speed (distance/unit time). So it would seem that the extra fuel per unit distance required to go faster would be proportional to the square of the speed, or maybe proportional to the square of the increment in speed, or maybe proportional to the difference in the squares of the speeds. You'd need to do some algebra to get it exactly straight. But as I said the proportionality factor is presumably much less than one. The formula given in the link could be used to calculate the factor for a given vehicle.

    But for any given vehicle, the best way to determine this would be driving different steady speeds (40 mph, 50 mph, . . .80 mph) and recording the instantaneous mpg values (or L/100 km values) shown on the fuel mileage computer display. I think these are pretty accurate, aren't they? Then you would just subtract to get the benefit from driving slower and the penalty from driving faster than the posted speed. To get the actual fuel and money saved you'd express the fuel use as gal/mi not mi/gal as we usually do in the US.
  • jim314jim314 Posts: 491
    I don't have a car with a mpg readout, but if anyone wants to do this here is some madeup sample data to show how it would be done, assuming level ground and the tranny in top gear:

    Speed(mph)..mi/galUS.....galUS/100mi....Fuel-Std 70mph*

    45..........35...........2.86...........-0.71 gal/100mi
    50..........35...........2.86...........-0.71
    55..........34...........2.94...........-0.63
    60..........32...........3.13...........-0.44
    65..........30...........3.33...........-0.24
    70..........28...........3.57............0.00
    75..........26...........3.85............0.28
    80..........23...........4.35............0.78
    85..........19...........5.26............1.69

    So if you want to know how much fuel you'd save on a 500 mi trip at 65 mph as opposed to 80 mph,
    Fuel saved = (0.78-(-0.24)) x 500/100 = 1.02 x 5 = 5.1 gal
  • jim314jim314 Posts: 491
    RE post #18:

    It would be much better to use the average mpg function of the computer, if it can be reset. The one computer I have seen in action is in my nephew's Jeep Grand Cherokee Ltd. As I recall the instantaneous mpg display is to the nearest mpg which is not really good enough precision. The ave mpg though is reported to the nearest tenth of a mpg. So you would estblish a constant speed and set the cruise control. Then reset the average mpg and then read it after a minute or two. Then go to the next speed, reset the ave mpg and read it after a minute or two, etc.
  • ateixeiraateixeira Posts: 72,587
    You'd have to make sure the road was perfectly level, though. Hills really throw the numbers off.

    -juice
  • kavoomkavoom Posts: 181
    I have an 04 X Forester manual. I have gotten as high as 31 highway mostly just above 29 mpg and generally in the 23 - 24 mpg range for other driving.

    I tow an 18 to 1900 lb pop up and have generally been at 21 mpg for three 3000 mile trips and almost 24 for one trip. Don't ask me. These are virtually all highway miles. I do know that the first three were through states where we were getting 10% ethanol for probably 2/3 of the gas.

    The last trip we also did a lot of driving without the pop up trailing behind.

    Not bad for these days.
  • ateixeiraateixeira Posts: 72,587
    Not bad at all.

    -juice
  • I own a 2003 Forester and get approx. 26 MPG. I love the vehicle and have had no prolems with it at 51,000 miles.
    The only issue was the mechanics who changed my oil didn't know that the o ring should be replaced when an oil change is done. It is in the book but I never read it! I had a small leak until I called Subaru and they made me aware of this.
  • I have tracked my 2001 Forester L (AT)'s mileage for the past two years. It has recorded a low of 20.27 and a high of 28.46, with a two-year average of 24.59 MPG, under an approximate split of 50/50 city/highway driving. The car has just about 90,000 miles now.

    The low of 20.27 MPG came about when it was 100% short city trips. The high of 28.46 MPG was a 100% cruise-set 55 to 65 mph driving.
  • In doing my homework to decide between an XT or XS Premium Package I keep having nightmares about lousy gas mileage with the XT. I live in the Boston area and the "get up and go nature" of the turbo is almost a life/death highway merging necessity ... but at what price? Is the XT's gas mileage really that much worse than the XS? I also noticed that 91 octane is required for the XT (ouch).

    Any cheap "real world" advice out there?

    Thanks,
  • terry92270terry92270 Posts: 1,247
    Ask a dealer about renting the L. L. Bean edition for a weekend, or an extended test-trial. Some dealers will do it.

    For city driving, the non-turbo certainly doesn't lack power, and I also do a fair amount of mountain driving with it, from Reno to Lake Tahoe, a 40 minute trip. And it uses regular unleaded. ;)
  • Thanks Terryl,

    I test drove both models yesterday and yes I was very impressed with the power on the XS. My previous 4 cylinder experiences include Ford Bronco II & Ford Pintos (ok stop laughing) ... so I was curious to see how far the 4 cylinders of today have come. Today's 4 cylinders are not those of the mid 80s for sure. But then I drove the XT and oh my gawwwwwd (I used to have a Turbo Trans AM as well) it was extremely impressive and I've seen its 0-60 ratings at around 6 seconds. I'm trading in a 6 cyl Grand Cherokee for a Forester and like I mentioned before, Massachusetts drivers are known as Massholes (sorry) for a reason ... they don't let you merge onto the highway ... you have to earn your way onto the road or :sick: else.

    Thanks again!
  • lfdallfdal Posts: 679
    Afraid so.. I live just north of Boston and on average I get 14-16 mpg in traffic, 24 on the open road (when I keep it under 80, BTW - that's very hard to do in an XT) ;) . My wife's 03 OBW in the same situation gets 18 and 27 respectively.
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