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Discussion Starter #1
We struggle to get the rated fuel economy most times. We usually chalk it up to payload weight- on any long freeway drives we tend to have a few hundred pounds of gear and a hundred and fifty pounds of dog. But every now and again, for absolutely no apparent reason, suddenly driving is effortless and the engine computer will start reporting 35 -40mpg instead of 20-25mpg. I make notes about tire pressure, air temperature, slope- but haven't figured it out.

Recently, mid-trip the numbers changed dramatically- which is significant because it suggests it isn't a question of payload.

We drove out to the west coast on I-80 towing a small trailer. Tires were set to 37PSI before we left (I juiced the rears because of the tongue load, but I've learned today it's apparently important to have the rears set lower). We've been running 87 or 88 octane. We drove 55-65mph the whole way. We were getting around 22-24 for the whole trip, UNTIL we hit California. We filled up shortly after getting down from the pass, and suddenly we were hitting 27-30mpg- exactly what I had originally hoped to hit, and what I had been told to expect (10-15% hit over rated with the particular trailer). I was even still hitting 27+ with short spurts of 70-75mph, and indeed I swear the Subaru suddenly felt like it wanted to go faster.

I've been wracking my brains to figure out what happened.

- Did the drop in altitude (much of I-80 west of Nebraska is 3-6k feet) make the engine run better? Of course, most people say they get BETTER mpg at altitude.

- Or did it change the tire pressure?

- Or is temperature a factor? It was forties and below across WY/UT/NV, but much of CA is mid-sixties during the day right now. This one seems unlikely, as we've owned the car for more than a year and driven through all sorts of weather.

- Is California running summer mix in mid March while the rest of the West is running winter mix?

- Is the road surface in California different, with less rolling resistance?

- What other variables have I missed?

We also reset the engine computer about a thousand miles ago due to disconnecting the battery while installing the hitch.
 

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2017 2.5 Touring
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One thing to keep in mind is that the EPA ratings are determined with straight gas, not 10% ethanol. Also, winter blends have butane added, to assist in sub zero starting. God only knows what your gas consists of, and you can't do much about it.
Also, trailers, no matter how light, drop your mileage. So do things on the roof of the car.
 

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Discussion Starter #3
One thing to keep in mind is that the EPA ratings are determined with straight gas, not 10% ethanol. Also, winter blends have butane added, to assist in sub zero starting. God only knows what your gas consists of, and you can't do much about it.
Indeed, I just wish I could isolate that factor & identify it, so I'm not pulling out my hair over it! Reading around, it sounds like entire refineries produce either winter or summer blends, and typically switch in later spring, so it seems less likely now that CA could be on summer blend while CO/WY/UT/NV are all on winter blends, especially in mid-March.

Also, trailers, no matter how light, drop your mileage. So do things on the roof of the car.
Naturally- I don't expect to hit 33 highway with the trailer! But, seeing as we didn't leave behind the trailer at the CA border, I figure it's not part of the sudden mid-trip jump in numbers :smile2:
 

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What road you roll into CA on? I’ve seen the same result but it wasn’t fuel related. I’m in CA btw. Your trailer must be pretty low profile to average 22-24mpg. I run 35psi in the rears when towing and packed. It’s a must or you trash the rear tires pretty quick.

4x6 900lbs empty around 1300lbs loaded. Sits about even with the rear window on the OB. We run 20-24mpg tank averages on trips with no Bikes on the roof. 18mpg with bikes
 

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2015 Legacy 3.6R ES, 2014 Forester Touring ES, 2005 Jeep Liberty Limited
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What you are seeing is point in time MPGs and not average. I am surprised you haven't seen 99+ on the gauge. It is not real, especially if there is crosswinds or winds from the back. So all the wondering is just a waste of time and has little bearing to the real world.

Laughing at oneself and with others is good for the Soul!
 

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.......We drove out to the west coast on I-80 towing a small trailer. Tires were set to 37PSI before we left (I juiced the rears because of the tongue load, but I've learned today it's apparently important to have the rears set lower). We've been running 87 or 88 octane. We drove 55-65mph the whole way. We were getting around 22-24 for the whole trip, UNTIL we hit California. We filled up shortly after getting down from the pass, and suddenly we were hitting 27-30mpg........with short spurts of 70-75mph, and indeed I swear the Subaru suddenly felt like it wanted to go faster.
Couple of things.

1) if you load the back of the vehicle, you'll need higher tire pressure. The front tire bias for running higher pressure is without a load. I run my vehicle f38/r34 psi, normally, but if the rear is heavily loaded, I increase the rear until off loaded, then return to 38/34.

2) Since you were on I-80, you do realize that from Truckee to Sacramento, its all down hill. You have gravity helping you roll down the freeway to give you higher speed and better milage.

Unfortunately, on your return, you'll likely to see worse than your original milage going up hill (Sierra mountains).
 

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2018 Outback Touring 3.6R
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Yoda, you made an excellent point. In southern CA there are often winds blowing from the east to west. He could easily have picked up a strong tailwind and not have been aware of it.
 

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2015 Outback Limited w/ES, Wilderness Green
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How do the computer numbers compare to actual hand calculated mileage?
I've got a 2015 OB Ltd 2.5 and have tracked mileage for 3 1/2 years, keeping records of both the car's indicated mileage and hand calculations.

On average, the car's computer is more optimistic by 1.5 mpg. The range of deviation between the two numbers varies from agreeing to the car being 2 mpg high. I don't think I've ever had a reading where the car was less optimisic than the hand calculation.
 

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I don't understand all the fuss folks make over the EPA ratings. It's just a number. Some hit it, some do not. Too many factors to truly determine why.

I pretty much always hit it in the OB. My wife rarely hits it in her Forester. We have two different styles of driving.

When she was recovering from knee replacement I drove her to PT in her Forester. After a couple weeks it was magically getting EPA rated mileage.
 
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I know you want to isolate, but you will live a lot longer if you accept the things you cannot change: Wind, gas makeup, grades, loads.
Get your tires aired up, drive below seventy, pretend there is a raw egg on the skinny pedal.
The rest is out of your control.
 

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I once got 37 miles divided by gallons for 250 miles at 70 mph with tailwind. With headwinds on return my 1000 mile trip average was 30. Calculated.

On 120 mile days at 55-60 mph I expect 37 mpg actual, nearly 40 on the fool computer.
 

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I don't understand all the fuss folks make over the EPA ratings. It's just a number. Some hit it, some do not. Too many factors to truly determine why.

I pretty much always hit it in the OB. My wife rarely hits it in her Forester. We have two different styles of driving.

When she was recovering from knee replacement I drove her to PT in her Forester. After a couple weeks it was magically getting EPA rated mileage.
I get better gas mileage in my Outback than my wife gets in her Crosstrek. She's got the lead foot in the family -- she had a Mini before getting the Crosstrek. :wink2:
 

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My best mileage to date was with a decent tailwind. It was on a 1,000 mile road trip where I averaged about 28MPG until the last leg. I went from having a crosswind a tailwind. The last tank was 30.8 MPG.

Back when I rode a motorcycle, the wind had a more noticeable effect. Highway riding usually returned 65-70 MPG on my NC700X. Rode with a sustained 30+ MPH headwind one day. Only got 45 MPG. Very frustrating going from a 210+ mile range down to 130 miles. Adds a bunch of extra, unplanned stops. Best mileage was riding through Colorado where a combination of tailwinds, high altitude (less wind drag) and lower speeds gave me 85 MPG.
 

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If you value numbers, here is some comparative data:

1) Based on tracking of nearly 2+ years, the computer estimate is a couple MPG rate is higher than measured value using actual distance and reported amount of fuel paid for at the pump. I average 25.8 MPG. Lots of city driving at 75 kph (46.6 MPH), but some freeway driving.

2) I have driven several times from SoCal to Colorado, and have achieved far better performance traveling west to east. I'm pretty consistent at 125 kph (77.7 MPH). (FYI: Only 1 ticket for speeding in 32 years. 85 MPH and it cost me $50. Keep it under 80 MPH, and you won't be bothered.)

3) Consumers Union, writers of Consumers Report, report 24 MPG for the 2.5 engine and 22 MPG 3.6 liter engine.

4) Any towing and all numbers go out the window. A neighbor, using a Hummer, towing a boat, complained about... are you ready... 3 miles per gallon.

If you really want good mileage in a larger vehicle, consider purchasing a Camary hybrid.
 

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I wrote about this topic a couple years ago and saw this topic on an update email from this Forum, (which I have not logged onto in over a year).

I believe the EPA mileage rating on the 2017 Outback Limited 2.5L is 26 – 33 mpg. This shows on the window sticker in the largest letters.

I have monitored my cumulative mileage average for 2 years and am at 26.5 mpg. I don’t drive erratically or rabbit start. As a matter of fact, I have changed my driving habits with this vehicle, focusing on even acceleration and keeping the engine rpm around 2000.

What I know, have learned and believe:

With outside temperatures over 47F I can get abt 30mpg on a relatively flat road and constant speed under 70-75 mph. At 55mph, I can increase that rate another mile or so. Seems an engine rpm of 2000-2200 is ideal.

With outside temperature below 47F and say 30F, I will drop 4 mpg.

What happens below 47F is the front grille dampers close. Subaru publishes that the grille dampers improve performance and perhaps they even use the word fuel economy, I don’t recall for sure. Subaru also published a coefficient of drag number, which looks good to us engineers. Subaru does not say that this coefficient was gather with the grille dampers closed or open. Puzzling me was an article I read on the current design (2015-present). The article mentioned how Subaru had re-designed the air flow pattern through the engine compartment to the underside of the vehicle and dispersing off the underside. I have search and re-searched for this article but cannot find it today.

I understand that ethanol, and winter blend, and change in elevation, effects fuel economy. This past February in my world, there would be one week of temperatures consistently below 47F and my weekely average was 24.5. The next week the temperatures were consistently above 47F when I was driving and my average was over 28. My driving paths and habits changed little.

I believe when the front dampers are closed, that drag coefficient increases. Common sense says if you put an obstruction in the air flow path, it will create resistance, make the vehicle work harder to achieve the same speed, using more fuel to do so. I believe the article I read about the engine compartment re-design for improved air flow is real. Doing this was a common engineering improvement during the years auto manufacturer where trying to improve fuel economy on vehicles. That the Outback has a somewhat flat front design is only exacerbated with the grille dampers closed. And the reason for the dampers?? Likely has to do with 2.5L engine efficiency when the temperature is below 47F. And as far as I know, Subaru doesn’t have this damper on the 3.6L.

I really like my Outback Limited. I choose a 2.5L, in part, because the mileage rating pleased me. Perhaps it was so pleasing because it is the first thing one see’s on the window sticker. In hindsight, I would have selected a 3.6L if I had known I would get 24.5 mpg at a temperature below 47F.
 

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You don't happen to be using the remote start or letting it idle at some times and not others are you? With my 3.6 I consistently get 27-28mpg, use the remote start just once or twice a tank though and it drops to 22-23mpg very quick.
 

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I believe when the front dampers are closed, that drag coefficient increases.
Highly unlikely.

Common sense says if you put an obstruction in the air flow path, it will create resistance, make the vehicle work harder to achieve the same speed, using more fuel to do so.
To paraphrase Theodore von Karman, the wind doesn't care about common sense. Aerodynamic drag results from the loss of momentum in the air stream as it flows around the exterior of the vehicle and through the radiator and engine compartment. From the standpoint of drag, it is more efficient to deflect air smoothly around the vehicle rather than allowing it to flow through the labyrinth presented by the radiator and engine compartment.

From Subaru tech training materials [AGAS = Active Grille Air Shutter]:
The AGAS is designed to improve fuel efficiency by improving body aerodynamics and decreasing
engine warm up time.
...
Note: The AGAS will remain closed if the ambient temperature is lower than 37 degrees
Fahrenheit (3 degrees C).


The opening and closing of the AGAS is determined by ambient temperature, coolant temperature,
and vehicle speed.
 
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After 7 years of driving our OB and this year doing a 200 km daily round trip commute to work, I can say with confidence that the on board mileage gauge is optimistic. I use my ultra gauge for a more accurate calculation but I use my fill up to do the math that tells the real truth. In good warm weather I avg 31 to 33 mpg imperial gallon. In cold winter weather I avg 29 to 31...ish mpg imperial gallon. It is no longer a mystery to me...weather, wind, roads (flat or hilly), load, these make all the difference in how well the car does on a tank of gas. I know that I can get 700km on a tank and last week was good week where my first 250km of the tank was a relatively flat drive so I was at just about 800km...but that is RARE!

Let's face it though...the mileage given to you when you buy the car...is optimistic and not the truth of what you are going to get in real world mileage...unless of course you drive a Diesel. Oh how I miss my 1000km tanks of fuel....:crying:
 
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