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Old 05-25-2013, 09:54 PM   #1 (permalink)
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Default Premium gasoline?

As I have mentioned in another thread, I am looking into purchasing my first Subaru. I have been reading about the 2014 Forester 2.5i CVT and once in a while people will strongly suggest using premium.

Is this necessary? Will I get horrible MPG or ruin my car if I use regular unleaded?

Thanks!
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Old 05-25-2013, 10:24 PM   #2 (permalink)
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The 2.5L engine is rated to use 87 octane (regular) at or near sea level - Use that :P
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Old 05-25-2013, 11:16 PM   #3 (permalink)
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Regular unleaded is just fine -- and recommended. Higher octanes are only beneficial in engines designed for them, generally preventing premature ignition (or "knocking") under high compression.

Because higher-octane fuels are marketed as "premium," there's a common notion that they're otherwise "better" and will benefit operation and performance. Actually, the opposite is true: engines not spec'd for premium will run less efficiently due to the fuel's higher ignition threshold. You're literally getting less bang for the buck and an accordant loss of power/MPG.

Best luck with your shopping, and welcome to the forum!

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Old 05-26-2013, 04:10 AM   #4 (permalink)
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Quote:
Originally Posted by Zappy View Post
As I have mentioned in another thread, I am looking into purchasing my first Subaru. I have been reading about the 2014 Forester 2.5i CVT and once in a while people will strongly suggest using premium.

Is this necessary? Will I get horrible MPG or ruin my car if I use regular unleaded?

Thanks!
Here's Subaru's guidance on fuel requirements for the U.S. market 2014 Forester (ref 2014 OM page 7-3):
Quote:
Non-turbo models

The engine is designed to operate using unleaded gasoline with an octane rating of 87 AKI (90 RON) or higher
Quote:
Turbo models

The engine is designed to operate at maximum performance using unleaded gasoline with an octane rating of 93 AKI (98 RON) or higher. If 93 AKI (98 RON) fuel is not readily available, unleaded gasoline with an octane rating of 91 AKI (95 RON) or higher may be used with no detriment to engine durability or driveability. However, you may notice a slight decrease in maximum engine performance while using 91 AKI (95 RON) fuel.

Regular unleaded gasoline with an octane rating of 87 AKI (90 RON) or higher may also be used. Using regular unleaded gasoline will not be detrimental to engine durability, nor will it affect your warranty coverage. However, depending on your driving habits and conditions, you may notice a decrease in maximum engine performance, fuel economy or slight engine vibration or knocking. If you experience any of these conditions while using a lower octane rated fuel, you may want to return to using 91 AKI (95 RON) octane rated fuel as soon as possible. Additionally, if your vehicle knocks heavily or persistently, or if you are driving with heavy loads such as when towing a trailer, the use of 91 AKI (95 RON) or higher grade unleaded gasoline is required.
I regularly experiment with this volatile issue . For your area's general elevation, I suggest you try 87 AKI (low elevation "regular") in the colder months, and 89 AKI (low elevation "mid-grade") in the warmer months. If you see no improvement when using 89 AKI fuel, then just run 87 AKI year 'round. However, operating with a full load and/or towing a sort-of heavy trailer (using Subaru tow specs) may warrant 89 AKI fuel, especially in the summer.

"Premium" fuel (93 AKI at low elevation) in a 2011+ Forester FB25 non-turbo engine would be a waste, IMHO. And, other than urban legend, I've not seen any evidence that would suggest premium grade fuel would harm your engine in anyway.

My '12 Forester delivered its best overall fuel economy run (mileage + distance) last September: 479 miles on 15.37 U.S. gal. of Shell 89 AKI from Erie, PA, to Guelph, ON, via Buffalo, NY, and then back through Buffalo to central PA. That was 31.2 mpg at a fairly low elevation (mostly under 1,000 ft).

Another good run was from eastern TN via I-26W, I-81N, and I-66E to northern VA in April, 2012: 416 miles on 12.99 gallons of a blend of 87- and 89 AKI fuel. That was 32 mpg.

We currently live is western NC at ~2,700 ft elevation. I've not seen any significant local fuel economy difference between using 87 AKI and 89 AKI fuels in the Forester. However, we experience an ~600 ft elevation gain over the last mile of road to our house, and the engine definitely pulls better on 89 AKI fuel. Specifically, there are two turns where I need to drop to first gear when using 87, but I can stay in second gear when using 89. It's an ignition timing thing...

And, a final comment regarding fuel octane (AKI) ratings and performance, and I love this one. Subaru of Australia specifies a fuel requirement of 90 RON (~86 AKI) for their new Forester with the FB engines. However, this disclaimer is added:
Quote:
@ All performance data measured using 95 RON as required by Australian Design Rule 81/02. Vehicles tested in accordance with ADR 81/02.
95 RON fuel is ~91 AKI in the U.S.

HTH,
Jim / crewzer
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Old 05-26-2013, 08:04 AM   #5 (permalink)
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Thanks everyone! I'll just go with the 87 off the bat.
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Old 06-05-2013, 01:16 PM   #6 (permalink)
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Crewzer, interesting data thanks.
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Old 06-05-2013, 08:48 PM   #7 (permalink)
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Dang, our "premium" in CA is 91 octane, what Subaru calls "regular" unleaded. That means the best gas I can get for my XT is what's considered barely acceptable. That sucks.
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Old 06-05-2013, 09:14 PM   #8 (permalink)
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Where do you see that? Says "regular 87 AKI (90 RON)". Our gas sucks because of ethanol content and price higher than in other states, but octane rating is high enough. Just stick to filling up at good stations and you should be okay.

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Old 06-05-2013, 09:31 PM   #9 (permalink)
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Originally Posted by stan_t View Post
Where do you see that? Says "regular 87 AKI (90 RON)". Our gas sucks because of ethanol content and price higher than in other states, but octane rating is high enough. Just stick to filling up at good stations and you should be okay.

Stan
Unless you can find ethanol free stations at pure-gas.org. I found one locally, and they proudly display that it's ethanol free.

I will warn though, ethanol free SUCKS to start in the winters. If it gets to below 20 degrees, the car will fight to start and stay running. But other than that, in the warmer months, I get smoother operation, better idle, better power, and improved fuel economy. Freaking love ethanol-free gas.
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Old 06-05-2013, 09:56 PM   #10 (permalink)
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Quote:
Originally Posted by stan_t View Post
Where do you see that? Says "regular 87 AKI (90 RON)". Our gas sucks because of ethanol content and price higher than in other states, but octane rating is high enough. Just stick to filling up at good stations and you should be okay.

Stan
It's in the quote for Turbo Models in post #4 above. Am I reading it wrong?
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Old 06-06-2013, 04:47 AM   #11 (permalink)
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It says the car is tuned for 93 octane, at least 91 is to be used, using 87 won't void warranty and if knocks use at least 91.

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