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Can anyone who uses both for their 6 tell me what significant differences they notice when using the different octane levels?
 

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Unless you're driving the turbo in a 2018+ model or have a tune specifically for that grade gas, the only difference you'll see is a lighter wallet with no perceptible performance change.


The 2.5L Skyactiv gas engine is designed for 87 grade. Going to a higher grade doesn't help (or hurt necessarily). Keep in mind there are no additional detergents or anything else that makes higher grade gas any better - unless your engine is designed to use it.
 

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Can anyone who uses both for their 6 tell me what significant differences they notice when using the different octane levels?
Some folks may like certain brands of 91 octane fuel which have no ethanol... Typically 87 octane has 10% ethanol. Ethanol can be corrosive but our cars appear to not have any corrosion of the fuel system prbs.

If you hav a tune that utilizes higher octane fuel for a benefit (say like strengthening your low rpm response a bit) - well then of course you'd use it.

Theoretically using higher octane fuel lessens potential fuel dilution of the motor oil... but folks on here have results which seem to indicate, no, this effect is not realized. The Skyactiv 2.5 does not appear to have a propensity to dilute motor oil with fuel, in general.

Some on here believe the economics are poor for upgrading fuel octane: too little benefit for too much incremental cost.

I can't say I notice any performance change in running 94 octane Canadian west coast Chevron.
 

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If you're running a turbo model run the 91+, if you're not run the 87. The higher octane prevents detonation, that's really it unless you're getting into the world of custom tunes.
 

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Unless you're driving the turbo in a 2018+ model or have a tune specifically for that grade gas, the only difference you'll see is a lighter wallet with no perceptible performance change.

The 2.5L Skyactiv gas engine is designed for 87 grade. Going to a higher grade doesn't help (or hurt necessarily). Keep in mind there are no additional detergents or anything else that makes higher grade gas any better - unless your engine is designed to use it.
In fact if you are in Colorado or other higher-altitude and "regular" is 85 run it -- even with an 87 tune. I've made a few trips out there, have seen no misbehavior, but what I HAVE seen is a material difference (higher!) in mpg.
 

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I have to run 91 in the winter in the 04 V6 as they put much too much ethanol in the lower grades. It's getting harder to find no ethanol premium grades now too. I get no performance boost of any kind. It does dramatically improve cold startups. As soon as the temperature gets over frerezing I stick to 87.
 

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Some folks have said that Shell (in Canada) has no ethanol in their 91 grade. I never thought to check.

Many years ago I had a '78 Chev Belair - 305 2V if memory serves... and it would lightly ping on much of the Shell fuel... versus NOT on the same indicated AKI / Octane for other brands... like Chevron (which we get on the west coast). Shell, it seems to me, was always stingy when it came to octane.

Having said this (and this was long, long ago) - Shell lubricants and fuel are I believe among the highest quality products in the market.

I like, though, the fact that I can get 94 octane Chevron... for my air-cooled Guzzi... and so I tend to patronize Chevron, all other things being equal.
 

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Many years ago I had a '78 Chev Belair - 305 2V if memory serves... and it would lightly ping on much of the Shell fuel... versus NOT on the same indicated AKI / Octane for other brands... like Chevron (which we get on the west coast). Shell, it seems to me, was always stingy when it came to octane.
My first 2 cars were 78 & 79 Impalas (US Impala = CA Bel Air) and I can vouch that the 305 was finicky when it came to marginal fuels. Car #3 was a 70 Caprice (ooh... I got chrome this time) with the 350/4bbl which never had issues with bad gas.


As for my Mazda, I switched to Shell exclusively and my MPG is currently about 10% better than the other readily available brands
 

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Check any pump you are not familiar with to make sure it is not posted as containing ethanol no matter the grade. They are sneaky about it.
 

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I have run 89 (mid grade) in my 2014 Mazda 6 since it was new. Works GREAT and the fuel mileage should be slightly better than with 87 octane fuel. Well worth the tiny difference in cost/mile.
 

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If I were in your situation I would run the 87. The only thing you should be making sure of is you are using a "Top Tier" fuel station.


Where we are we get 87 or 91. We run 91 because of the turbo. Bought the car in part because of the extra power. The higher the octane the more HP/TQ. Wouldn't make much sense not to feed it. That and the 91 is only 20 cents @Gal more than 87. Less than $3 a tank for the 91 almost pays for itself with the slightly better gas mileage. Approx 1 mpg better for us.
 

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I have run 89 (mid grade) in my 2014 Mazda 6 since it was new. Works GREAT and the fuel mileage should be slightly better than with 87 octane fuel. Well worth the tiny difference in cost/mile.
I've been doing the same probably 90% of the time, unless the price difference for 89 feels too high.

I can't say my testing is scientific, but it seems to be good for about 1 MPG, and also seems to start/idle a little better when it's cold. That could be in my head though.
 

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Discussion Starter #14
I definitely will try 89 or 91 on my next fill up because it won't hurt to experiment and see the difference! Thanks for all the input guys :)
 

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Big difference here in price (~30 cents/gal for mid-grade and ANOTHER 20-30 cents/gal for 92/93!, so 50 cents/gal+ for "Premium") Not worth it. I have a 92 tune calibration file but don't load or use it due to the ridiculous price difference in the fuel here.

One thing I CAN tell you for certain though -- when out in the mountains "regular" is 85. The SkyActiv engine runs perfectly well on it and *that* makes a considerable difference in fuel economy -- +2-3mpg! So yeah, if I'm out there I buy it, and the car has no complaints running through the full tank I leave CO with when I get back into Texas at MUCH lower elevation either.....
 

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Well, ok, you do what you want.

I have (more than once), my engine is still in one piece, I'm OVTuned, and by Ghod, I really enjoyed the additional distance I traveled on a given tank.

Again: You do what you want.
 

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Let's think about this for a minute, ok 4
 

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A few "partial truths" in there and possibly incorrect conclusions:

Using a higher octane gasoline will not help clean your engine. The U.S. Environmental Protection Agency requires all commercially sold gasoline to contain engine cleaning detergent additives that can help extend the life of your vehicle.
While The EPA does require a minimum amount of detergents, the oil companies can use additional detergents; such as Top Tier additive packages.



The Difference Between Premium and Regular Gas
Simply stated, premium gas has a higher octane level than regular gasoline.

You have a lot better chance of finding ethanol-free premium than lower grades. I know in your home town you have the RFG garbage, but once you hit the normal gas zone the only offerings of 100% gas are all 91 octane.
There are very few cars that will not see a performance and efficiency gain from the omission of alcohol
 
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