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Discussion Starter #1
Just took a 800 mile road trip with my 2015 Outback. It had 24K miles on it with a Thule Atlantic roof cargo box. Mostly highway driving 75 to 78 mph with cruise engaged, temps around 35 degrees thru OH & IN. Averaged 22 going and 18.5 coming home against a stiff oncoming wind. I'm hoping without the cargo box I can get closer to a 30 mpg average. I thought the Outback would be a lot better than my old Chevy Tahoe that I owned for 20 years and got 16.5 mpg average for it's entire life.
 

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I simply cannot abide useless people.
2006 2.5i and 2002 3.0 wagons.
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75-85MPH with a cargo box? Yeah, that's about right.

Slow down and lose the box unless totally needed.
 

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2018 Subaru OB Premium
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The faster you go the more the car fights air, the closer to 65-70 the better MPG's will be on all cars, and if the cruise is like my Nissans it's awful for fuel economy on anything but flat roads

Currently averaging 26 I think in mine combined, I see 30+ on the highway here in the mountains all day
 

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2015 Outback Limited, 2.5i, 2021 Touring XT in White
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Some time ago, someone posted the average highway speed for the EPA was 48 mph. So any speed more than 48 will give you lower MPG. Test are also conducted using ethanol free gas with a driver who is very experienced in EPA testing.
 

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2018 Touring 3.6R
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Some time ago, someone posted the average highway speed for the EPA was 48 mph. So any speed more than 48 will give you lower MPG. Test are also conducted using ethanol free gas with a driver who is very experienced in EPA testing.
It's correct that the average speeds of the hwy tests are around 48mph, but there's far more to it than that. One of the hwy tests is basically a mix of city and hwy driving with multiple brisk accelerations, full stops, idling, and an 80mph top speed. The other is a more rural highway mix, but still has lots of speed changes and a top speed of 60mph. Those tests only cover 8 and 10 miles respectively. None of the EPA tests reflect a long distance relatively fixed speed highway only run, which is why MOST cars at the very least hit their EPA numbers on those trips. Many vehicles with decent aero easily beat those numbers. I have a sedan that is usually 5mpg over on long trips.

Our OB averaged 29mpg on a 300 mile highway only trip which is 2mpg over EPA. That was 75mph, winter fuel, and only about 1,500 miles on the car at the time. I won't be surprised if 30-31mpg is common in the summer.
 

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2016 2.5i Limited, 2013 Tesla Model S 85
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Our OB averaged 29mpg on a 300 mile highway only trip which is 2mpg over EPA. That was 75mph, winter fuel, and only about 1,500 miles on the car at the time. I won't be surprised if 30-31mpg is common in the summer.
29 MPG at 75 MPH is the best argument I have heard justifying a 3.6. Especially if at temperatures below 40°F. At cold temperatures I can’t get that out of my 2.5 at 70 MPH. But I can reliably get 35 MPG at 55-60 MPH in warm temperatures. And 27 MPG around town. Calculated MPG, not the fool computer.
 

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2014 Subaru Outback 2.5L CVT (Alloy Wheel Package)
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Its the cargo box. I normally get 24mpg city and 30mpg hwy, but if I mount an overhead bike rack with wind fairing and a couple bikes on it, the mpg goes down to what your getting.
 

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Just took a 800 mile road trip with my 2015 Outback. It had 24K miles on it with a Thule Atlantic roof cargo box. Mostly highway driving 75 to 78 mph with cruise engaged, temps around 35 degrees thru OH & IN. Averaged 22 going and 18.5 coming home against a stiff oncoming wind. I'm hoping without the cargo box I can get closer to a 30 mpg average. I thought the Outback would be a lot better than my old Chevy Tahoe that I owned for 20 years and got 16.5 mpg average for it's entire life.
75-80mph with one of those wide short boxes thats right. Add even a light head wind and it could knock you into the 18mpg tank average range. Simple slow down and the mileage will rise. 100,000 miles with our OB the highest tank averages were Eastern Oregon 55-65mph with our narrow and long roof box which typically runs around 1-2mpg hit at 75mph. That was 34mpg over a 520mile run. 65mph our box is a zero hit. But the wide short boxes are closer to 3-4mpg hit at 75mph.

75mph I5 in CA with a head wind and box 24mpg tank average is typical for us. No head wind 26-28mpg tank averages are typical. Two Mountian bikes plus box 75mph us a 18mpg tank. 65mph and under withbikes and box on the lid is 28ish.

No box I5 in CA 70mph tops SF to LA no head wind 30mpg is doable. Traffic and sub 70 speeds 32mpg tanks have been seen many times.

Box plus our 900lb 4x6 loaded to about 1300 for camping trips no bikes on the lid 65-70mph 22mpg tanks are the norm. Bikes added 18mpg tank averages.

Our 4.7L Sequoia with same trailer and box returned 16mpg SF to Twin Falls ID at 80mph. Same stretch with head wind 15mpg.

7 days motoring around Yellowstone and Grand Teton no trailer sub 50mph speeds we saw a tank average 21mpg all time highest ever tank average we’ve seen in that rig.

You want 30+mpg in the Subaru you need to skip the box and run low 70’s max speeds or run the box at 65mph max.

Or just buy my wifes Fusion Energie she averages 80-85mpg every week.
 

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The only non hybrid type car I have ever broke 30+mpg tank average at 75-80+mph road trips is our fun play car SLK 350. That car has a crazy low drag coefficient and 290hp v6 with a 7spd its not even breathing hard till your in 3 digits. 80mph for 1000 miles is like a walk in the park.
My elder father inlaw did a 620mile single tank run in it!! No doubt taking his sweet time!! The Subaru OB isn’t a super sleek ride and drag is the biggest mileage killer. Higher the speed the drag factor multplies
 

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29 MPG at 75 MPH is the best argument I have heard justifying a 3.6. Especially if at temperatures below 40°F. At cold temperatures I can’t get that out of my 2.5 at 70 MPH. But I can reliably get 35 MPG at 55-60 MPH in warm temperatures. And 27 MPG around town. Calculated MPG, not the fool computer.
I don't recall the temp on that trip but it likely was cold. It's been the only time I drove the car long enough to call it highway only. My wife regularly does a ~300 mile trip but she doesn't manually check it. Or care. I did some testing last week on a long stretch of flat highway comparing the displayed mpg at 70 vs 75 and really didn't see much of a difference. Both were right around 32-33mpg when you could keep everything steady. There's also a discussion elsewhere here about how the 2.5 raises the RPMs to ~2,300 with cruise control engaged. Ours stays right at 1,900 with/without cruise. I would bet if you hypermiled the 2.5 and didn't use cruise you could turn some impressive numbers.
 

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I've logged some impressive MPG totals while driving in higher elevation areas. I've logged some impressive MPG numbers driving from Clayton, NM to Southfork, CO. You'd think the less dense air would impact not improve MPG.
 

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You'd think the less dense air would impact not improve MPG.
Nope. Lower air density means lower aerodynamic drag, as well as higher engine efficiency due to decreased pumping losses.
 

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Since early Nov., with the 3.6R, I've been right in the estimated fuel economy range. With mixed driving, little above 22 mpg. With good highway driving almost 27 mpg.
I've not found a secret for improving city mpg. Highway mpg is heavily tied to speed.

The craziest fuel economy I ever had was in the 1990s with a 1991 Acura Integra. While its fuel economy was rated at 21/26 mpg...at a near constant 80 mph, it would get over 40 mpg, repeatedly. It was like you broke into some strange new time/space continuum, it didn't make sense, but a buddy of mine had the same experience.

It would be nice if Subaru added more smart engine technology and other efficiencies for improved fuel economy. In the past decade, many manufacturers have seen some huge advances in fuel economy along with an increase in power/acceleration. It's hard to believe but the "old" traditional F150 with 5.4L V8, 6sp got around 14 mpg, whereas the 2018 2.7L V6 Turbo, 10sp, gets 19 mph with a 0-60 time of 6.8 secs. Subaru is moving towards this with smaller, turbo charged engines but remember we will always take a hit with the AWD.
 

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Discussion Starter #15
MPG was calculated, not based on cars trip computer. Tire pressures were set to recommended psi on door. Tires are Bridgestone Blizzaks. Might be able to lose the rooftop cargo box on future trips. Thanks to all for the responses.
 

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Check your tire pressure.
This is the one ding I'd give the dealer

I checked the pressure on the little read out on the way home and the dealer had all 4 tires pumped up to 40 PSI, and when I got home I lowered them down to near where they needed to be.
 

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This is the one ding I'd give the dealer

I checked the pressure on the little read out on the way home and the dealer had all 4 tires pumped up to 40 PSI, and when I got home I lowered them down to near where they needed to be.
The reason I brought it up, is most folks don't check the pressure when the weather goes from warm to cold, once winter sets in the air pressure will drop substantially per tire giving your terrible mileage if you don't adjust for it.
 

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The Bridgestone Blizzaks are costing you about 3 to 4 mpg.
If you get the cargo box and Blizzaks off the car, you will be increasing your mpg roughly 6 to 8 mpg (maybe more).
 

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The "sweet spot" for MPG is between 45-55 MPH. Any speed above that will reduce your MPH in a logarithmic manor. (sorta like the Decibel scale) ... the fuel-consumption goes up much faster than your MPH increase.

I once went on a trip (over 8 hours driving) with 2012 Outback and PURPOSEFULLY stayed off the interstate highways. Averaged between 45-50 MPH (except for the little towns/bergs).... the resulting MPG was the HIGHEST I ever recorded on that vehicle.
 

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Just took a 800 mile road trip with my 2015 Outback. It had 24K miles on it with a Thule Atlantic roof cargo box. Mostly highway driving 75 to 78 mph with cruise engaged, temps around 35 degrees thru OH & IN. Averaged 22 going and 18.5 coming home against a stiff oncoming wind. I'm hoping without the cargo box I can get closer to a 30 mpg average. I thought the Outback would be a lot better than my old Chevy Tahoe that I owned for 20 years and got 16.5 mpg average for it's entire life.


For reference, I take an 800 mile road trip every week going 70-80mph, 400 miles to WI from and 400 back to MN, I average about 6mpg better than your trip, but I don't have a box. As it warms up my mileage improves to about 32-34 in summer. Wind can make a big difference.
 
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