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Better mileage from premium gas? #4098046 05/16/16 07:37 AM
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SubieMovie Offline OP
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Just a question. Although the Crosstrek manual states that regular gasoline should be used, I put 4 gallons or so of premium fuel a few weeks ago and saw roughly a 6 mpg gain.

I'm running regular again and it's fallen back down to Earth.

Do the Boxer engines run better on premium or is this just imagined placebo [censored]?

I wouldn't mind throwing a blend in there if it meant a decent boost in mpg.

Re: Better mileage from premium gas? [Re: SubieMovie] #4098051 05/16/16 07:41 AM
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Quattro Pete Offline
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If you could truly gain an additional 6 mpg by running premium, Subaru would be mandating you to run premium in order to claim much better CAFE MPG numbers.

IMHO, there is no way you're gaining this much just by switching to premium.


2002 530i   2015 Q5 3.0T   2018 Charger SRT
Re: Better mileage from premium gas? [Re: SubieMovie] #4098056 05/16/16 07:47 AM
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kschachn Offline
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The energy content of gasoline is irrespective of the octane rating - assuming it is all gasoline. If it is a blend of gasoline and ethanol then that does not apply. Some regions/stations sell premium that is E0 instead of E10, that can make a difference.


1994 BMW 530i, 251K
1996 Honda Accord, 280K
1999 Toyota Sienna, 430K
2000 Toyota ECHO, 284K
Re: Better mileage from premium gas? [Re: SubieMovie] #4098058 05/16/16 07:48 AM
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Reggaemon Offline
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Both of my Subarus get the same mpg regardless of the grade or brand of gas used.

Re: Better mileage from premium gas? [Re: SubieMovie] #4098063 05/16/16 07:53 AM
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Miller88 Online Content
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Some vehicles can see an increase with premium fuel. Higher resistance to detonation means that the ignition timing can be advanced.

DI engines, higher compression engines will see at least a slight increase in fuel economy for sure. My parents got quite an increase in fuel economy switching their Ecoboost Escape to 91


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Re: Better mileage from premium gas? [Re: Miller88] #4098069 05/16/16 07:55 AM
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Benzadmiral Offline
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Originally Posted By: Miller88
Some vehicles can see an increase with premium fuel. Higher resistance to detonation means that the ignition timing can be advanced.

DI engines, higher compression engines will see at least a slight increase in fuel economy for sure. My parents got quite an increase in fuel economy switching their Ecoboost Escape to 91

Last summer I tried 93 E10 in my 2.4L DI Ecotec engine. While I saw a small boost in economy, it wasn't enough to offset the extra cost of the 93. So I stick with 87 now, usually Exxon. The Regal seems to get the best mileage on it, and I get a .06/gallon "loyalty reward" rebate on each gallon I buy.


* *
-- Paul W. (The Benzadmiral)
('16 Buick LaCrosse Premium, 3.6L, deep garnet/light neutral)
http://benzadmiral-uncle.blogspot.com/
Re: Better mileage from premium gas? [Re: SubieMovie] #4098078 05/16/16 08:05 AM
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dparm Offline
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To be as scientific as possible, you'd need to keep the conditions exactly the same tank-to-tank. In the real-world, that's virtually impossible.

Only way I can think of to definitively measure this would be to either run several premium tanks and work very hard to keep conditions nearly the same, then run a few regular tanks and replicate those conditions.

Alternatively, if you have some datalogging software, check if the timing is being advanced while running premium. If it is, that means the car is taking advantage of it.


2017 Chevrolet Corvette Grand Sport
Re: Better mileage from premium gas? [Re: SubieMovie] #4098082 05/16/16 08:11 AM
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FutureDoc Offline
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A few engines can get a small bump, but it normally is not enough to offset the price-point. Often you would need one of two things, an engine that was converted to "accept" regular after being designed around premium... or a higher-compression (sometimes a turbo) DI engine that has knock sensors designed around different octane/HP abilities. One good example of the higher-compression/turbo engine is GM's GenIII Fam0 1.4T DI engines. Cruze/Encore/Spark owners see a mild bump. Something like 5-10% but not often enough to make-up the cost in gas. I have seen this when driving my mother-in-laws Buick. However, I can not completely discount error in this observation as the difference could be cause by other spurious factors. On the other hand, I think I could get a bump on my DI Hyundai as I have different EPA HP numbers for the Genesis Coupe. Have not tried it yet.

For Subaru, only the old EJ2.5 Phase I could/would see a bump. Mostly this was because the first EJ2.5 were designed to use Premium and then were later reworked for "regular". So 1995 required Premium but 96-99 could run "regular". I have tested this out with my '99 and I might see 0.5-1mpg (5%) if I am lucky. Not enough to to rule out random error.

Thus with your MPI 2.0, I would keep to regular.


'15 Hyundai Genesis Coupe 3.8 - Havoline 5w-30 & OEM
'14 Subaru Outback 2.5 - NAPA 0w-20 & Wix
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Re: Better mileage from premium gas? [Re: SubieMovie] #4098134 05/16/16 09:17 AM
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Jetronic Offline
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seems the answer is: depends on the vehicle...


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Re: Better mileage from premium gas? [Re: Miller88] #4098136 05/16/16 09:21 AM
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bubbatime Offline
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Originally Posted By: Miller88
Some vehicles can see an increase with premium fuel. Higher resistance to detonation means that the ignition timing can be advanced.

DI engines, higher compression engines will see at least a slight increase in fuel economy for sure. My parents got quite an increase in fuel economy switching their Ecoboost Escape to 91


Absolutely 100% correct. Some high compression engines will run 87 octane, but the computer retards the timing to prevent detonation. When you fill it back up with premium, the computer advances the timing to where the engine runs optimally, and thus increases fuel mileage. My Acura has 11 to 1 compression and will get about 1 mpg boost running premium fuel.


2019 Honda CRV 1.5T dealer bulk
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Re: Better mileage from premium gas? [Re: SubieMovie] #4098201 05/16/16 10:26 AM
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I've never noticed a difference in fuel mileage on any vehicle I've owned in the past, but my current Cruze Eco definitely gets better mileage with mid-grade or premium. It has smoother power delivery and the calculated mileage is better by a noticeable amount. The mpg's showing in the trip computer don't show it is any better, but in warmer weather the calculated mileage is much less than the trip computer if running 87 octane. Running 89 octane or 93 octane and the calculated and trip computer are very close. You can actually feel the timing get cut back and power drops under certain circumstances when running 87 octane. In the winter I run 87, and 89 octane the rest of the year.

Each car type is different in how it responds.


1996 Buick Roadmaster Wagon
2014 Cruze Eco Manual
2003 2500 Suburban, 8.1L
Re: Better mileage from premium gas? [Re: SubieMovie] #4098221 05/16/16 10:45 AM
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racer12306 Offline
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Makes me curious to do a test. I've been tracking everything about my car since I started driving it regularly again back in October.

My driving is so consistent that I could feel I could accurately test something to determine effectiveness.

Seems if I can make my drive with zero or very minimal traffic delays, it returns between 34.0 and 34.6 MPG. As soon as traffic gets thrown into the mix or more than one trip of local driving it dips to 30-32 MPG depending on the situation.


16 Ford Focus/2.0/6A
04 Dodge Neon SXT/2.0/MTX
17 Chrysler Pacifica/3.6/9A
Re: Better mileage from premium gas? [Re: SubieMovie] #4098266 05/16/16 11:28 AM
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I've only seen an improvement of 1-2 mpg using Shell V Power 91 which is E0 up here. Essa, Petro Canada, Ultramar and Husky premiums are all E10 and I've not seen any change with those. I think in the average engine, ethanol content has more of a fuel economy effect than octane rating


2011Toyota Matriix
2016 Nissan Rogue


Re: Better mileage from premium gas? [Re: SubieMovie] #4098272 05/16/16 11:36 AM
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surfstar Offline
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^bingo

If 91+ gets you E0, vs E10, then yes, you may actually get more MPG.


2016 Golf Sportwagen 5MT M1 0w40 LC20 RLI BioPlus
my other vehicle is a Roth IRA
Re: Better mileage from premium gas? [Re: SubieMovie] #4098284 05/16/16 11:53 AM
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1000MPH Offline
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I've been tracking the mileage on my 4Runner since new. I do a 360 mile one-way trip about 15-20 times a year. I usually stop at the same gas station and same pump. This trip is done very early in the mornings with little to no traffic. Mileage results are all over the place with the only real measurable being a consistent 10% drop in the Winter months (approx dec-feb) on the outbound leg.I've tried multiple tanks of premium but cannot track results accurately enough.
The biggest obvious factor is winds.


2010 4Runner 106k mi M1 EP High Mileage 0W-20 OEM filter cartridge. Delvac synthetic gear 75W-90.
2015 Rav4 47k mi M1 EP 0W-20 OEM filter cartridge. Delvac synthetic gear 75W-90.
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