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Discussion Starter · #1 · (Edited)
'014 Touring was getting an average at the Easy Coast of 33 MPG and 36 (and my wife could nail 38 MPG regularly out west) at my Colorado home in the summer, but now in November I'm lucky to squeeze out 30 MPG average. Local Service tech blames the decrease on the winter blend gasoline. So is 10% loss about right or is it because of, or in addition to buying new tires? I really like General Altimax HP-43 tires; cheap and quiet. I can't believe the OEM Yokahamas nor winter blend gas could make that much difference. I have to drive like a granny to get the 30 MPG when in the summer I didn't think about it. Any thoughts:icon_question:
 

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My cars also achieve better fuel economy at altitudes such as those in Colorado. I attribute it to lower aerodynamic drag due to thinner air (low air pressure).

I'm not a big fan of the "winter blend" theory behind reduced winter fuel economy, at least not as the primary cause. Instead, everything else being equal, I believe that winter aerodynamic drag is higher due to more dense air that's both colder and drier. The higher drag leads to lower fuel economy.

The Department of Energy makes this statement regarding season fuel blends:

The energy content of gasoline varies seasonally. Typical summer conventional gasoline contains about 1.7% more energy than typical winter conventional gasoline.

At 30 mpg, a 1.7% difference in energy content may result in a fuel economy difference of ~0.5 mpg.

Check your tire pressures in the morning when they're cold, even if it means leaving the car outside (not garaged) overnight. Cold ambient temperatures lead to reduced tire pressure, which in turn leads to reduced fuel economy.

Other factors that can reduce winter fuel economy include longer warm-up times and frequent use of the windshield defroster, which turns on the a/c compressor when outside temps are above freezing. Subaru claims the OEM tires are "low rolling resistance". The Altimax tires' RR may be higher because they're new and/or their overall design.

Finally, Subaru recommends using 87 AKI or higher fuel in your non-turbo '14 Touring; see page 7-3 in your OM. Although it may seem to run OK on 85 AKI (= high-elevation regular) at high elevation, it may actually do even better on 87 AKI (= high-elevation mid-grade).

HTH,
Jim / crewzer
 

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2014 Forester XT Touring CVT
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Winter blend fuel contains more Butane than regular summertime fuel does.

Butane contains fewer carbon atoms, and since it has fewer carbon atoms, it burns less efficiently.

Here is a better article I have been sharing in a few other threads about the winter blend fuel.

What You Should Know About The Fuel You'll Be Putting In Your Car Soon

It mentions a loss in MPG between 2-8%.

I have noticed a drop close to 10% in my 2014 XT, but it is likely more sensitive due to the turbo.
 

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I just did a 13+ gallon fill-up with 91 octane ethanol free gas today. Will see how it compares with my prior tank of 87 octane and 10% ethanol. I have a few friends with outbacks who report getting better mpg with this gas so will see. Though I doubt any mpg increase will pay for the higher cost of the gas. I am doing it just as an experiment.
 

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Discussion Starter · #5 ·
This winter (maybe) MPG reduction is new to me as I've just ditched my diesel Jetta to buy the Forester. I think its a tire issue more than a fuel issue. BTW, does anyone know why gasoline is 85 octane in higher altitudes and 87 octane at lower? Lower air density means less detonation? I too think the air density has something to do with how easily a car slips through the air molecules, but I can't imagine it would make a 10% difference.
I'll be interested in seeing how the straight up 91 octane does for you. I'm paying about $2.75 for regular Shell here in Virgina so ten percent of that is around a .30 per gallon penalty or $4.00 loss per fill-up. So paying .30 more for ethanol free fuel would be a break even think.
 

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I'll be interested in seeing how the straight up 91 octane does for you. I'm paying about $2.75 for regular Shell here in Virgina so ten percent of that is around a .30 per gallon penalty or $4.00 loss per fill-up. So paying .30 more for ethanol free fuel would be a break even think.

Wow you guys have some cheap gas. I am paying $3.40 + for 87 octane. The ethanol free premiums was $4.01. So I guess they are charging a premium for ethanol free premium.....ha! :icon_biggrin:
 

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Wow you guys have some cheap gas. I am paying $3.40 + for 87 octane. The ethanol free premiums was $4.01. So I guess they are charging a premium for ethanol free premium.....ha! :icon_biggrin:
87 w/ ethanol is down to $2.58 here in OKC. Premium with no ethanol is around $3.25 - $3.50 or so I think.
 

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My winter mileage in NJ always drops, regardless of the weather conditions and regardless of the vehicle I'm driving. Seems to start sometime in September. Yes, the winter blend gas does adversely affect mileage and it really bugs me.

I guess the claim is that it's supposed to reduce harmful emissions, but if it makes vehicles burn gas I have to wonder just how much it's reducing those emissions.
 

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Does gas have anything to do with it or is it just the cold? Tires get stiffer, oil in gear boxes and differentials thickens, all moving parts stiffen up. When we buy fuel it comes out of the ground (usually). The fuel tank in your car is exposed to the weather so the fuel cools and contracts. Is cold gas less responsive?

Snow tires are notorious for reduced fuel economy, partly from tread design but also from stiff rubber after sitting over night. Tire pressure has to be watched closely in the winter because it will go down with the temperature. Un-watched tires will soon be under-inflated.

Then, there are those who idle their engines to warm the passenger compartment.
 

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Does gas have anything to do with it or is it just the cold?
The gas definitely has something to do with it.

I am sure some of those other things have an affect too, but fuel is a definite contributor to the loss.

Winter blend fuel contains more Butane than regular summertime fuel does.

Butane contains fewer carbon atoms, and since it has fewer carbon atoms, it burns less efficiently.

Here is a better article I have been sharing in a few other threads about the winter blend fuel.

What You Should Know About The Fuel You'll Be Putting In Your Car Soon

It mentions a loss in MPG between 2-8%.

I have noticed a drop close to 10% in my 2014 XT, but it is likely more sensitive due to the turbo.
 

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Has anyone tried the "midgrade" option?...around here it's usually 89 octane (which is obtained by mixing premium 93 octane with the 87 stuff) and ~ $0.15-$0.20 more per gallon...it might justify since my calculated average has dropped from 30.5 to around 28 MPG
 

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Has anyone tried the "midgrade" option?...around here it's usually 89 octane (which is obtained by mixing premium 93 octane with the 87 stuff) and ~ $0.15-$0.20 more per gallon...it might justify since my calculated average has dropped from 30.5 to around 28 MPG
I don't think the octane is the issue. More all the crap they are putting in the winter blend. I am running a tank of 91 octane only because that is the only octane locally that can be had without ethanol. Though even that may have other stuff in it that I am not aware of.
 

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Running a higher octane is not going to do anything.

The only reason to run a higher octane fuel in a vehicle tuned for 87 octane would be if your engine was knocking when running that octane fuel.

Octane controls how early the combustion takes place. Higher octanes = later combustion. Lower octanes = earlier combustion.

THE TRUTH ABOUT WINTER GAS. BY JOHN HUNKINS

Winter fuel blends would have much lower octane levels than summer blends. Because of this, they have to add oxygen-bearing components (with very high octane levels 100+) to regulate the octane. These oxygen-bearing compounds take the place of some gasoline, so it takes more of the gasoline to get the job done.

So, regardless of what octane fuel you run, you are still going to see the same results. You might actually see a decrease in MPGs running a higher octane fuel because you engine is not tuned to run on it (unless you have an XT).

Some quotes from the above link:
The trick is to have the right fuel for the right time of year. In the summer, when the temperature is high, the presence of too many light components will cause the fuel to evaporate too readily. This can result in vapour lock, an over-rich mixture and excessive evaporative emissions. In the winter, too many heavy components keep the fuel from evaporating, causing hard starting, a lean mixture, heavy hydrocarbon emissions and poor converter light-off.
For reformulated winter gas, lighter, low-boiling-point components are added to the gasoline to increase volatility. This makes your car easier to start and accelerates converter light-off, thus lowering emissions. That's the official line on reformulated gas.
 

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yes, i am getting 1-2 sometimes 2-3 mpg lower according to my screen reading on my '14 premium 2.5i. I used to hover around 30, but lately its been closer to 27-28. I dont account for the load startups i get too waiting for the blue light to go away which takes like 4 minutes now that is it colder.
 

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yes, i am getting 1-2 sometimes 2-3 mpg lower according to my screen reading on my '14 premium 2.5i. I used to hover around 30, but lately its been closer to 27-28. I dont account for the load startups i get too waiting for the blue light to go away which takes like 4 minutes now that is it colder.
I don't wait for the engine to warm up completely before leaving, it wastes too much fuel IMO. I'll idle for a minute or two, then go. I keep the rpms below 3000 until the cold light goes out. Once I'm on the highway I'm only cruising at around 2,500 rpm anyway so I'm not concerned.
 

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anyone know when the winter gas starts flowing in our pumps in the northeast (US)

I've been closely averaging my MPGs with my all seasons before the switchover to winter tires. guess I'll have a double whammy knock-down in MPGs with tires & winter gas
 

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yea I typically give it 30-45 seconds to get the oil circulating then take off. Does the owners manual recommend waiting for the blue indicator light to go off? If not I doubt very much that it is necessary.
 

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anyone know when the winter gas starts flowing in our pumps in the northeast (US)
It has already happened, I can assure you of that.

I have seen as early as September 15th.

Standards for June 1 to September 15 are maximum standards for all regulated parties including retailers and wholesale purchaser-consumers, unless state has an extended summer season as part of the federally-approved SIP
Guide on State Summer RVP Standards | Fuels and Fuel Additives | US EPA
 

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Discussion Starter · #19 ·
yea I typically give it 30-45 seconds to get the oil circulating then take off. Does the owners manual recommend waiting for the blue indicator light to go off? If not I doubt very much that it is necessary.
All I've read says to do exactly what you're doing. Idle for the shortest period to get oil flowing and then drive off keeping the speed low until engine warms.
 

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The octane rating does and can affect fuel economy. As stated earlier, a lower octane fuel burns faster and higher octane fuel burns slower which is an over simplistic way to look at it. Low octane fuel has a lower resistance to detonation and burns faster during combustion. This is bad because combustion can happen too soon in a motor rated for a higher octane fuel which will cause engine damage from the air/fuel mixture igniting too soon and pushing down on a piston which is still traveling upward toward top dead center. To offset this, ignition timing is reduced such that the ignition happens several degrees of crankshaft rotation later. The bad part is this reduces power since timing is reduced all along the spark table. Idle and cruising spark doesn't change much, but any point at which the motor comes out of vacuum and goes into boost will experience ignition timing that will be reduced considerably.

Reduced in timing means the engine has to work harder which equals reduced fuel economy for a turbocharged engine.

Conversely, running a higher octane fuel in an engine designed for low octane fuel will actually reduce power because of its longer combustion time.
 
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