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Regular or Premium

144K views 347 replies 81 participants last post by  hokiefyd 
#1 ·
I wanted to find what type of gas is recommended in Subaru? I am coming from the last 4 cars going back to 2010 that required Premium gas. I am hoping to finally get into a car that uses regular
 
#8 ·
Thank you. I am not a speedster anymore. To hard to drive really fast on Long Island without having to worry about an accident or cops and the north shore is so over populated and full of traffic lights. I generally drive to and from work, sometimes to NYC, and a lot of of driving to Montauk, or Orient Point to fish.

As long as it doesn't say Premium required I am good.
 
#9 · (Edited)
From experience owning our 2014 Forester XT (including driving cross country at multiple altitudes), even though the engine "can" run regular per Subaru and the owner's manual, you really do not want to. The ECU can detect the lower octane fuel (and likely knock events from the knock sensor) and reduce ignition timing, etc. When this happens, you get less power (obviously) AND worse fuel economy. This information is spelled out in section 7-3 of the 2014 Forester Owner's Manual. The power and fuel mileage reduction is noticeable, even if only running one tank. So, even from a cost perspective (due to MPG drop using regular), it make sense to always run Premium fuel in the Forester XT FA20DIT.

However, Subaru RECOMMENDS using premium fuel in the Turbocharged Forester XT. If Subaru engineering has done all of their testing, tuning, and other evaluation using regular 87 octane fuel AND recommends using a minimum of regular 87 octane in the Ascent, there is a chance that premium fuel will NOT be needed to meet the published power and MPG figures. With how Subaru has been publishing everything thus far, this should be the case. That being said, using premium fuel for additional safety margin to prevent knock (which will cause the ECU to limit optimum performance) is always a good idea. If Subaru says the Ascent will make 260 hp, 277 lb-ft, and get 27 mpg highway with regular fuel, do NOT expect improved horsepower or MPG above the published specifications by using premium fuel.

In the end, we all need to wait and see what is printed in the owner's manual and see how this new engine responds to different fuel grades. Until then, we are all guessing based on previous experience with the FA20DIT and other conjectures.
 
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#24 ·
This is absolutely untrue. If the ecu cannot compensate and was designed for 87 running 91 will only cause you to spend more money. 87 has more energy than 91 the benefit in 91 is it burns slower letting you run more timing which the ecu can be tuned to get more power from.
 
#23 ·
even here in UT, i always run 87, and never 85 unless im feeling super cheap and having to fill up my Jeep (gets crap for mileage anyways). I will probably run premium (91 i think in UT, dont recall as I dont have to use it) for most of the long road trips and 87 for most around town things.
 
#28 ·
I'd be curious to see what the Costco Gasoline comes in at. They advertise all over that they have 5 times (5x) the number of detergents compared to whatever "normal" Top Tier fuel is.

But, like you pointed out, not sure if that's referencing 87 or 93. They only offer 87 and 93 at my local warehouse.

Also, with these engines being DI - you should always put in top tier fuel. Always.
 
#32 ·
Ok, so... based on the list from the news article, if you go with the NON Top Tier brands on the list, and multiply by 5, that's 26mg per ml, which beats all the other tested brands except Shell at 31mg. Shell is the lowest 87 octane top tier and the lowest detergent level of the ones tested (ironic, since they're the highest detergent level as well, when you look at their 93). 16.2mg times 5 would be 81mg... hmmm... maybe I need to renew my Costco membership... I can get 87 octane and all the detergent I could ever want.

So, either way, it sounds like Costco (any octane) or Shell (93 octane) are the best choices from what little information we have... intriguing.
 
#29 ·
Ok, now this topic (best gasoline for keeping the engine clean) is really getting me digging.

Here's a 2011 "Investigative Report" that says similar to what I found:
>> https://www.kshb.com/news/local-new...nts-that-can-affect-mileage-may2011swp?page=2

Note that Shell is best for 93, and Exxon/Mobil best for 87... Shell still leading the pack at all levels.

Here's a video version:


This could be where the data for the spreadsheets I found online came from.

CountryMark claims to have twice the required amount of detergents... (I've never heard of them, but it may help others near a CountryMark supplied station):
>> https://www.countrymark.com/country...hings-You-Didn-t-Know-about-TOP-TIER-Gasoline

Current licensed Top Tier brands:
>> https://www.toptiergas.com/licensedbrands/
 
#31 ·
I found this... straight from the Costco website.

Description: Costco website says the only difference between 87/93 is the octane rating. Same detergents.

Now, the million dollar question is to figure out a way to compare Shell and Costco... ;)
 

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#33 ·
Since higher octane gasoline is not required, buy regular and place a priority on getting a Top Tier gasoline that has additives. I will stop at Costco when convenient and check Gas Buddy for other stations along the way. I used to go to the Safeway station close to my house, but they refuse to control the traffic flow going in and out and that caused frequent conflicts getting to the pump. After several requests to get a handle on that, I told them that I would never buy gasoline there and also discontinue shopping for groceries. Last I checked, it appears that my patronage was not missed. I stopped using their Bio-Diesel in my Sprinter because the source was sketchy as is their gasoline. Besides, their Bio-Diesel makes the exhaust smell like French fries. I used to think someone made that up until it happened to me. I started to use the Kroger station more because they have a queue to get to the pumps, but their gas is also not Top Tier. My 2014 Forester was getting a bit rough at idle. I started to use Top Tier exclusively and after two tanks, I can feel the difference. My Forester has port fuel injection. My 2017 BRZ has port and direct injection and is on an exclusive diet of high octane Top Tier gas. The Ascent is direct injection only and I read all there is about the downside of a direct fuel injection only engines. I think the jury is still out on that, but Top Tier gas will have some benefit.
 
#34 ·
Since higher octane gasoline is not required, buy regular and place a priority on getting a Top Tier gasoline that has additives.
The problem is that Shell 93 blows away every competitor tested - by a LOT. They also blow away their 87 octane. Costco makes a claim that would mean their 87 is at least near equal to Shell's 93.

So, maybe Costco 87 (or any octane) is the way to go?

The only definite "known element" is that Shell's 93 is far superior to anything tested.
 
#39 · (Edited)
High octane fuel is generally made for cars that have higher compression ratios. In these cars the lower octane fuel will ignite too early, causing engine knock and performance suffers. The higher octane fuels burn at a higher temperature.

It is a waste of money to use an octane fuel in that is higher than recommended or use high octane when you don’t have an engine knock problem.

Here’s a source with more info:

https://www.consumer.ftc.gov/articles/0210-paying-premium-high-octane-gasoline
 
#41 ·
High octane fuel is generally made for cars that have higher compression ratios. In these cars the lower octane fuel will ignite too early, causing engine knock and performance suffers. The higher octane fuels burn at a higher temperature.

It is a waste of money to use an octane fuel in that is higher than recommended or use high octane when you don’t have an engine knock problem.

Here’s a source with more info:

https://www.consumer.ftc.gov/articles/0210-paying-premium-high-octane-gasoline
That's true but this car is turbocharged. You will most likely gain performance when using premium. It's not a waste.
 
#44 ·
FYI: Subaru's answer to this question has been a consistent "87 octane or better".

You'll find actual emails quoted in these forums. Unless @pilot1226 gets a more specific and contrary answer back from SoA, I'm sticking with the higher octane due to better detergent.

I would consider Costco since the detergent and additive levels are only a little less than Shell's, but I no longer have a membership and don't plan on renewing. So, in the meantime, I'm doing Shell 93.
 
#49 ·
From Costco:

Thank you for your inquiry about Kirkland Signature Gasoline! If you go to www.costco.com and search: Gasoline, there is an entire website of information about our Gasoline. We believe our fuel quality is second to none.

Our detergent additive package is independently registered with the EPA. The Top Tier program is administered by General Motors, and supported by several other automakers such as Toyota, Honda, BMW, Mercedes-Benz, VW, Fiat Chrysler, Audi and Ford. www.toptiergas.com

In order to qualify and meet the performance standards for TOP TIER, an additive must contain about three times the EPA detergent requirement. Costco's Kirkland Signature Gasoline additive dosage is five times the requirement, which provided the maximum cleaning impact during our engine testing. We additize with the same dosage in both our regular and premium grades, which is 5 times the lowest additive concentration (LAC) allowed by the U.S. Environmental Protection Agency (EPA).

Read more about fuel quality at the following:
The Costco Connection - April 2014:
http://www.costcoconnection.com/connection/201404#pg37
AAA Newsroom with Press Release and Infographics:
http://newsroom.aaa.com/2016/07/aaa-not-gasoline-created-equal/

Sincerely,
Costco Fuel
 
#50 · (Edited)
The owner’s manual of my 2009 Subaru Impreza (non-turbo) says the same thing, 87 octane or better. I’d be willing to bet any semi-recently made car supports the same when it was designed for 87. The engine can adjust the timing to support the higher octane gas, the only difference is the price you’re paying at the gas station.

I’ll tell you what—I’ll put 87 octane in my tank, you can put 91 (or 93+) in yours. At 50,000, 100,000, and 150,000 miles we can compare how much we’ve spent in total on engine repairs and gasoline. (Hint: by 150,000 miles you’ll have spent about as much as the cost of a new engine on the price difference of premium fuel. In other words: it’s not worth it)
 
#51 ·
To summarize your valid point, if all a person cares about is cost, then use the cheapest gas supported.
I'd be interested to see if there's any difference on a dyno, but I'm not willing to pay for it.
I might use the cheapest Costco gas until COBB comes out with something for the Ascent or Subaru comes out with an explicit update that supports higher octane levels.
 
#53 ·
I have put 87 in the vehicle so far - just put 2000 miles on the car loaded with kids and bags (although this is probably only like 750 pounds total). I'd probably put 93 in when towing. I imagine the motor will detonate from time to time on 87 when it is hot and heavy and 89, 91 or 93 will help to prevent this and possibly give you a few extra hp.
 
#67 ·
Reading all your posts about how awesome Costco has is makes me sad that the nearest one is about 70miles from me. Never having a turbo engine before is both exciting and a little worrying as far as the gas I should be using. I have had my 4.7L V8 for 11 years and just put in the 87 at the gas station up the street which happens to the the cheapest gas within a 20mile radius. No engine issues ever, just every single recommend service and my Chrysler has never missed a beat (only had the alternator replaced). Do I just run with this cheap 87? Go to the Shell station across the street and get the 93? So many people question??? I don’t mind spending $12 to $15 more per tank...
 
#68 ·
Go with the recommendation of the engineers that built the car. This engine is different than any other Subaru has produced and I assume it's why their recommendations for fuel are different for the Ascent vs. the WRX, STI or Forester XT
 
#74 · (Edited)
You can still do stupid stuff the computer may not be able to compensate for, like put it into manual shift mode and then floor it at 1500rpm going up a hill on the highway. If you are in "automatic" mode it's less likely to allow you to do stupid things that it can't compensate for. Just driving around on 87 you should be fine. Towing I'd definitely run the highest octane available because you will be seeing heat and engine load you do not typically see.

At 15k mile a year 91 ethanol free or 93 e10 does add up to $300+ a year difference for me. I'd bet you'll get a few HP out of running higher octane because the fine learning may add a few degrees of timing here and there .
 
#76 ·
Can’t find ethanol free near me so my option is 87 Costco or 93 Costco. Or another brand.

Apparently the person that runs the fuel division for Costco is going to call me to talk about my concerns on top tier and the carbon buildup. Anyone want me to ask something special? Again he is Costco fuel, not Subaru, so he can’t comment specifically on the FA24.

The big question I have is if the 93 will actually harm the exhaust system of the Ascent. My gut says no, but someone on another forum said that since 93 burns slower it actually ends up with more unburned fuel getting into the exhaust system which is problems for the catalytic converter?
 
#77 ·
Costco has some of the best fuel and a lot of detergents. You should be fine with Costco 87. In fact I'm waiting for the Costco to open across the street from my office. They just pushed back the opening to September and I'm shocked with how quickly the building is going up.
 
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