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2010 FORESTER 2.5XT LTD
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Discussion Starter #1
Hey All,

Just heard some conflicting reports about which type of fuel I can use with my new 2010 Forester XT Limited (Turbo).

The Subaru site says "Recommended" fuel is 91 octane (Premium Fuel). One service manager says if I use regular fuel my engine will break and there is no warranty. Another service manager at a different dealership says his customers use regular fuel all the time!?

Please help.

Thanks.

D.
 

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05 FXT Broken 5-speed
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240 Posts
Use the highest octane fuel you can find on a regular basis and can afford. Even, up here in Denver, Colorado, 91 octane seems not even good enough, for Subaru's crappy factory tune. Usually, when we baseline, prior to tuning, there so a lot of knock (detonation).
I switched to E85, tuned it through OpenSource (Ecuflash and RomRaider). Never had a knock-count since.
Most of the time, I have to pull 5-12 degrees of timing, from the Subaru factory tunes, on turbo Subies.

Subaru's ECU logic is smart enough to pull timing, and add fuel, when it sees detonation. But that still doesn't mean it will save your engine.

I bet, if we pulled your car's history, using the Tactrix cable and Romraider's Learning View, you would see knock counts.
Absubtle
CO
 

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2017 Foz 2.5i CVT
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I assume you have an owner's manual. Read the section on fuel requirements. It says you can use regular gas *temporarily* if premium is not available. I read this as emergency use only.

I would never run a turbocharged or supercharged car on regular gas as a long term diet. The effective compression ratio is much too high and although the electronic controls will keep the plugs and pistons from melting (and they would have in the old days), the engine systems are compromised and performance will be reduced.

George
 

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It would look something like this. This is a 04 STI, the negative values is timing being pulled.
This is not too bad of a learning view, I will save the next one I pull.
Absubtle
CO
 

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2010 FORESTER 2.5XT LTD
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Discussion Starter #7
I assume you have an owner's manual. Read the section on fuel requirements. It says you can use regular gas *temporarily* if premium is not available. I read this as emergency use only.

I would never run a turbocharged or supercharged car on regular gas as a long term diet. The effective compression ratio is much too high and although the electronic controls will keep the plugs and pistons from melting (and they would have in the old days), the engine systems are compromised and performance will be reduced.

George
Hey George,

You are correct. My bad. I just got the car a few hours ago and it wasn't until 3 minutes ago that I decided to RTFM (read the manual). :icon_biggrin:

Quote from manual: "NOTE: Be sure to use premium unleaded gasoline of 91 AKI or higher for turbo engine models. If other gasoline (lower than 91 AKI) is used, knocking, reduced output and poor accelerator response will result."

That seems pretty clear. Everyone one on here was correct. That dude at the dealership had his info all wrong. My only concern is that I drive quite a bit and often in small towns across western Canada where there may not be 91AKI octane fuel. I just bought some "Octane Booster" and left them in the trunk just in case this happens. Hopefully, octane booster actually works in this case.

Thanks all.

D.
 

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2010 2.5 XT Limited
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348 Posts
I use 91 which is the highest octane I can get around here. I wish they have 93 here or even 97 and 98 in the U.S.... LOL
 

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2010 Forester
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High octane is usually 91 or higher. That's what the manual wants, and that's what I've done for the MY10 FXT for it's 6000 mi.

There are a lot of cars out there that are designed for premium, but allow regular, and whoever wrote their manual figured thatit would not cause a warrantee claim in 60,000 miles. But NOT Subaru!!!

Using $2.80/G for reg and $3.00/G for premium, the cost of using prem (assuming a 22 mpg comsumption car) is $.009 (roughly one cent) per mile more with the premium. That is equivalent to driving a car that uses 24 mpg rather than 22 mpg. This calc does not account for possible mpg improvements associated with using the higher octane fuel as recommended, which could possibly reduce the cost/mile differential.

Bottom Line: It is NOT worth risking damage to an engine for the equivalent of a 2 mpg savings.

Bob
 

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Octane booster doesn't do much aside from cost extra money. Most octane booster only does about .1 of an octane.

Also, the ECU only has a certain range it can adjust timing stock. If the fuel is too low octane it will still knock even if the ecu compensates. I know on my XT it knocks even if not driving too hard on 87, but 89 it can deal with it seems. If you have to use regular, try to stay out of boost as much as possible.

Also, the XT will get worse gas mileage if it retards the timing, so you'll get the best fuel mileage on the highest octane (within reason) you can find. I've found mine actually costs less per mile when running 93 than it does on 89,87 etc.
 

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Discussion Starter #11
High octane is usually 91 or higher. That's what the manual wants, and that's what I've done for the MY10 FXT for it's 6000 mi.

There are a lot of cars out there that are designed for premium, but allow regular, and whoever wrote their manual figured thatit would not cause a warrantee claim in 60,000 miles. But NOT Subaru!!!

Using $2.80/G for reg and $3.00/G for premium, the cost of using prem (assuming a 22 mpg comsumption car) is $.009 (roughly one cent) per mile more with the premium. That is equivalent to driving a car that uses 24 mpg rather than 22 mpg. This calc does not account for possible mpg improvements associated with using the higher octane fuel as recommended, which could possibly reduce the cost/mile differential.

Bottom Line: It is NOT worth risking damage to an engine for the equivalent of a 2 mpg savings.

Bob

Yeah Bob. Absolutely right.

I did a calculation last night for fuel costs up here in Canada based on an average of .10 cents difference between regular and premium fuel and came up with almost your exact numbers as well.

On my 2010 Foz there is a fuel consumption display that shows average fuel consumption. It's freaks me out everytime I touch the gas pedal on a green light cause it shows consumption at 50L/100km ha ha ha ha.

Can't wait until I reach 1,600kms so I can start driving this car the way I want!!

D.
 

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2009 Forester XT Limited
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Apparently this stuff works for some folks but from what I can tell, the lead isn't much good for the O2 sensors and I have no idea what it would do to a turbo.

I too was looking for a solution if low octane fuel is the only thing available but I am not recommending this stuff for us, just saying it actually works for some folks and it would be nice if there were a lead free alternative but from what I can gather, the lead is what makes it boost the octane efficiently.

http://www.batterystuff.com/fuel-treatments/OS6q.html
 

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Discussion Starter #13
Octane booster doesn't do much aside from cost extra money. Most octane booster only does about .1 of an octane.

Also, the ECU only has a certain range it can adjust timing stock. If the fuel is too low octane it will still knock even if the ecu compensates. I know on my XT it knocks even if not driving too hard on 87, but 89 it can deal with it seems. If you have to use regular, try to stay out of boost as much as possible.

Also, the XT will get worse gas mileage if it retards the timing, so you'll get the best fuel mileage on the highest octane (within reason) you can find. I've found mine actually costs less per mile when running 93 than it does on 89,87 etc.
Thanks. I'm gonna return these Octane Booster additives. I checked my "routes" across Western Canada and there are Husky Gas stations in each small town. Husky shows a "Premium Plus" fuel of 93 Octane! Whoa. I wonder what they charge for this extra octane gas? I know Esso only goes up to 91Octane and they charge .12 cents more than regular on average.

However, your post and this topic has certainly got me thinking I should spend the extra $$ and change gas stations from Esso (goodbye Aeroplan miles. Waaaa) to Husky (Hello CAA/AMA rewards. Meh) for the extra octane premium fuel.

D.
 

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Thanks. I'm gonna return these Octane Booster additives. I checked my "routes" across Western Canada and there are Husky Gas stations in each small town. Husky shows a "Premium Plus" fuel of 93 Octane! Whoa. I wonder what they charge for this extra octane gas? I know Esso only goes up to 91Octane and they charge .12 cents more than regular on average.

D.
Chevron usually has 94, at least here in BC they do.
 

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I use 98 Octane every time all the time - runs like a beast!

04 -2.5X
I note that you're in Australia. The US (and it looks like Canada as well) have a system where they average "motor" and "research" octane and get lower readings. This average is what the government requires be posted on our pumps.

When I was drag racing in the 1970's, I remember Sunoco 260 pump gas was the highest octane available at 102, but that was the higher "research" octane number. Leaded Super Shell, which I used a lot, was 100 research octane. (For the record, I had a couple 426 Chrysler hemi cars including a 12.5:1 compression Hemi Cuda...)

"Motor" octane is 8-10 points lower than research octane, so the current US average octane ratings are 4-5 points lower than in the old days. That means the old leaded Sunoco 260 would currently be rated at 97 or so, and Super Shell at 95.

I'm guessing your 98 octane gas is the same as our current 93 octane... :icon_biggrin:

edit--yup, Australia and Europe show the higher research octane numbers http://en.wikipedia.org/wiki/Octane_rating

George
 

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2007 Forester XT Sport
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My foz LOVES the higher octane gas. I get far better gas mileage on 93 than 91. Sadly we have to cross into TX to get 93 without paying $5 a gallon at the one local station (no joke). Also avoid the 10% ethanol stations if you can. And old stations with old pumps, I've gotten bad gas before and it is NOT pleasant. Luckily for me, my tuner is not only my best friend but also works with me. So if somethings not running right, he can pop into the parking lot and fix it. Most don't have this luxury. Even with 91, I would get an aftermarket tune for it to avoid knock at all.
 

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Discussion Starter #18
Man, this forum is AWESOME! If it wasn't for you guys I would have been tempted to take the advice from the dealership who said regular 87 octane gas would be fine most of the time. Love my new FOZ but DYING to reach 1,600kms so I can have some fun with the turbo. I'm at 160kms. Meh.
 

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Man, this forum is AWESOME! If it wasn't for you guys I would have been tempted to take the advice from the dealership who said regular 87 octane gas would be fine most of the time. Love my new FOZ but DYING to reach 1,600kms so I can have some fun with the turbo. I'm at 160kms. Meh.
Paitience! :biggrin:
 

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2009 Forester XT 4EAT
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Man, this forum is AWESOME! If it wasn't for you guys I would have been tempted to take the advice from the dealership who said regular 87 octane gas would be fine most of the time. Love my new FOZ but DYING to reach 1,600kms so I can have some fun with the turbo. I'm at 160kms. Meh.
Yes, you can usually find lots of good information in the forums. If you're bored at work, spend a couple of hours searching through the archives. :biggrin: Ummmm...well...no...I would never do that while at work.. :icon_rolleyes:
I might also add that the "service manager" that gave you advice on using regular unleaded....I'd avoid him like the plague.
 
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