# Subaru Forester MPG-Real World Numbers

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272,587My average improved by about +3mpg after a year or so, that would put you in the low 20s at least.

-juice

1,878Stop racing those CRVs :P

15.5 XC70 T6 / 16 Soul EV / 17 Toyota 86

291I'm a little disappointed with my new Forester's mileage. I'm on fill up number three and I get a little over 18 MPG in the city. Does that seem right?Let's define "in the city," first -- are you talking about going 95%+ of a tankful driving on actual city streets? You know, stoplights at every intersection, rarely traveling above 30 mph, lots of idling?

If that's the case, I'd actually be pretty happy with 18 mpg. I live in New York City, and on those occasions where we go a whole tankful w/o ever leaving the city limits, driving exclusively on local surface streets (no intracity jaunts on the highway), I've gotten as low as 15-16 mpg in the summer (AC).

I have a 2004 Forester, which lacks throttle-by-wire and a couple of other refinements that yours has, so I wouldn't imagine you'd ever end up that low. But if you're talking about extreme conditions like the ones I outlined above, then 18 mpg doesn't shock me.

FWIW, I get about 27-28 on all-highway driving (rare for us) and 23-25 on "mixed" (almost every tankful we drive will be at least 50% hard-core urban mileage). I had one tankful just over 30 mpg, driving 45-55 on rural back roads in Ohio. EPA for my model is 22/28.

Hope that helps. I'm not thrilled with my urban mileage, either, but I think it's got more to do with the conditions than with the car.

22113I think an engine should be fully broken in within 2-3000 miles, really there isn't that much lapping/wear-in happening. I'm not unhappy with the 20-21, was just hoping for 25ish with careful driving.

67Two real-life examples:

I have a commute that occasionally goes 28 miles one-way. In my prior car (an old BMW), I could see the difference in economy by watching the range (miles to empty) number during the commute. This number would drop steadily over the first 10-12 miles, then start holding steady and then increase slowly over the second half of the trip.

Wife has a Prius with an LCD display with MPG charting capability. It shows the MPG in a bar chart. Each five minutes another bar pops up with the previous 5-minutes measurement, and so after 30 minutes you'll see 6 bars showing the MPG for each 5 minutes during that span. The first bar always shows about 25 MPG, the next one is about 40 MPG, then each succeeding bar shows 45-55 mpg depending on the terrain. Should it be any surprise that said wife gets under 40mpg for her 2-mile commute when I get 50 or better on weekend jaunts over longer distances? (EPA for '02 Prius - 52 city/48 hiway). Granted, the Prius is an extreme example since the gas engine doesn't run all the time, so it should take a bit longer to get to maximum operating efficiency. (It runs for a minute or two at startup to heat up the cat converter, then it runs as needed afterwards.)

Bottom line, you really need to be driving longer distances in order to see MPG numbers approaching the published EPA numbers. Say, 15-30 miles at a time, not 6 miles.

Break-in. 10,000 to 15,000 miles is a more realistic break-in period. You'll see a gradual rise over that time, I'd say about 1-2mpg, eveything else being equal.

13I love this car, it just feels unusually solid and smooth. When your biggest gripe is that the radio blanks for a half second coming off "scan", I'm really having to stretch to find anything to not like :-)

The big moonroof, feel like I'm just a notch down from a convertible.

First few days with the new Forester, had this weird feeling that I could almost forget that it needed to be driven. The old 92 Loyale never felt that way, kept me on my toes.

Do boxers minimize thermal mass, standing coolant in the engine? Warm up time is amazingly fast, the old Loyale was great that way too.

67The car it replaced (old Beemer 525i) took an extra 2 miles to get to the same point. Dunno why, I'm thinking the Beemer had a bigger radiator. 2.5 liter engines in both.

72,587-juice

714,423-Frank

7,717It's a Tuesday, how could I be bored???

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4,423-Frank

10,059tidester, host72,587Peak of 30.4 mpg on a trip.

Low of 17.3 mpg while towing a 1500 lb trailer the entire time.

-juice

67October thru April - 28 mpg

May thru September - 30+ mpg

(difference due to seasonal temp variation (eastern Pennsylvania) and winter gas additive changeover at refineries)

Best mpg - 32.3 on 440 miles (same tank of gas) mostly long distance. Last month.

Worst - first tank, at 24.5

72,587-juice

3,613best: 26 mpg (all highway at 75 mph)

worst: 18 mpg (winter)

average: 21 mpg

Average mpg up until this past winter was 1 mpg better than my Outback. Partial thanks to winter fuel, no doubt.

-Brian

3,613Averaged 26 miles per day, or about 9,500 miles per year. 87 octane from Super America. Reformulated fuels and winter blends both with 10% ethanol.

best: 28 mpg (highway trip)

worst: 17 mpg (again, winter)

average: 22 mpg

-Brian

1- 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

3,613-Brian

235Filled 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

72,587Try 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

223I did notice that mileage improve markedly after ~7500 miles or so.

67How 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.

491The 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.

10,059The 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, host491That 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 consumedper 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.

491Speed(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