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*The Electrician*
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Discussion Starter · #1 ·
Just wanted to quickly check what everyone is using for fuel octane on the 2.5L Skyactiv. Im sure the manual will say regular 87 Octane but they say that about the new civic turbo(non-si) and Im told their having many issues because of that. Which serves them right for trying to run variable octane in a turbo motor hoping the ECU will accommodate it. I have a local gas station that runs no ethanol so Im good there as I hear ethanol blended fuel is bad for direct injection engines. I have the availability of many Shell gas stations too but I would have to run 91 Octane premium to get past the ethanol blended low/mid grade fuel they carry here. Yes, the highest octane they have here without being ethanol blended is 91 octane, sad i know. If you want higher octane there are stations which carry 94 octane but its ethanol blended.
 

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Gearhead
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1,841 Posts
Our engines are direct injection motors, and as such need special gasoline additives to reduce underside valve and other engine part carbon build up. Top Tier fuels have those extra additives. We use 99% Shell, Chevron and Texaco, but if not available, carry with us a list of Top Tier fuel brands.



Both AAA and ConsumerReports have researched and concluded that running Top Tier fuels is better for your car, and financially worth it.

Leave it to others to reports to your good questions about octance, benefits of ethanol free, etc.
 

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*The Electrician*
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Discussion Starter · #3 ·
thx for that report, I've been using Co-op and was told previously that its on par with what Shell has available. Im saving that report to show others.
 

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Owners manual says to use good quality 87 octane or better for the 2.5. I have always used Premium (usually Shell V-Power) 91 octane in my 2017 Grand Touring 2.5. Locally, all regular and mid-grade fuel is required to have 10% and 5% ethanol respectively, so I have been using premium since that law came into effect in protest (I don't agree with the politics of corn ethanol). In my previous car there seemed to be a trend of getting better gas mileage with premium 91 over regular 87, which would make sense since there is no ethanol in it, but I don't have enough hard data to back that up.

Use a quality 87 octane and you should be fine.
 

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I agree with Road Trip regarding using Top Tier fuel in a DI engine. But as far as octane - if your engine was designed to run on 87, that's what you should run. Ideally the ECM would just adjust by advance timing until the knock sensor detects pinging and run right at the edge increasing performance but I don't think they program in that much leeway (thus the 91 octane tune, 93 octane tune, etc). And yes, you will get worse mileage using ethanol blend vs. straight gas but around my neck of the woods they only have ethanol free in the highest octane and charge an arm and a leg for it. Not worth it for me. Just wait for the 15% blend to hit the streets:surprise:
 

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98 and only ever bp..
 

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I have a 2015 3sGT with the 2.5L and manual transmission. I run 85 octane, but I'm in Denver and the car has never gone below 1 mile altitude. No knock. No problems. I would use higher octane if I were taking a road trip somewhere lower.

I always fill up from a local Phillips 66, Shell, or Conoco. Top Tier only. It has ethanol but I still get great MPG. No complaints.
 

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I use 87 - Tier One maybe every tenth fill-up, and then because that's most convenient.
 

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Engine is designed to run on 87, that's what you should run. No benefit for higher octane, may not be better to run higher octane all the time even if you can.

Top Tier gas is more important then the octane for Mazda's.
 

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My 2014 got regular any brand and never had an issue. The 2017 will get the same.
 

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Also depends on the price of gas too. Toronto is seeing almost $1.40/L for 91 which makes it extremely high given the price of $1.11/L for 87. No way to justify 91 at the moment. Maybe if the difference was at most $.15 then would I consider 91.
 

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*The Electrician*
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Discussion Starter · #13 ·
Also depends on the price of gas too. Toronto is seeing almost $1.40/L for 91 which makes it extremely high given the price of $1.11/L for 87. No way to justify 91 at the moment. Maybe if the difference was at most $.15 then would I consider 91.
Pretty much the same in Alberta
 

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Gearhead
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We took our 2017 WRX (my daily driver) on a road trip through British Columbia and Alberta last September. It requires 91 octane. When comparing apples to apples (conversation of the USD to CAN, size of a "gallon/vs liter", etc) we paid between $5.15 and $5.40/US gallon. Spendy, but I will use lower than recommended octance.

The fact that our new Mazda GT uses regular fuel is a really nice asset -- and one of the reasons for us buying it.
 

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*The Electrician*
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Discussion Starter · #15 ·
The fact that our new Mazda GT uses regular fuel is a really nice asset -- and one of the reasons for us buying it.
That was my hope as well, I assumed it would be ok on regular but wanted to double check with everyone on here. Im glad I checked on here too as I learned about top tier fuels.
 
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