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The only reason to use higher-octane in the SkyActiv engines is that they will pull timing at lower RPMs under high-torque demand driving conditions (to avoid detonation) and you can feel it when it happens. It doesn't do any harm and using higher-octane fuel won't give you better mileage, but might give you a tenth faster 0-60 time. Worth it? I say no and run 87.
 

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The only reason to use super unleaded is that some older engines prefer no ethanol. My 6 runs/starts better when cold in the winter when running 91 octane. Up here they can ram up to 15% ethanol into lower grades of gas.



It doesn't make my car have better performance or get better mileage, it DOES help cold starts very noticeably. I notice no difference in high octane gas once the ambient temp is 40F or higher though.
 

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You do realize, don't you, that this thread is over 12 years old?

What is your point? Did you even take the time to look and see that it is a very active thread that has been replied to ALOT over the years, including this year?


Last thing we need around here is a self appointed mod.
 

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What is your point? Did you even take the time to look and see that it is a very active thread that has been replied to ALOT over the years, including this year?


Last thing we need around here is a self appointed mod.

Self-appointed mod? Really.

This post was answered on the very first page. What could you possibly hope to add to that?
 

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I found 2 stations in my town selling 93 ethanol free. I am not sure if it js merey a placebo effect or what but to me, it sounds a bit throatier, and of coarse i think it pulls better. Also, 87 reg if i fill the tank to the brim i might get 385 mi on the dash, alternatively with 93 e-free i get avg 427 mi. Hit sport mode when those pesky civics and obnoxious stock mustangs come knocking i catch myself doing 110 in no time and the opponents start looking smaller in the mirrors. That 427 per tank is out the window 20181029_214901_1540875826223.jpg
 

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Higher Octane? Not necessary

Hi, im just wondering what octane gas I should use. In the owners manual is says to use 87, but to my knowledge isn't 91 always better. 91 octane is supposed to be for, correct me if im wrong higher compression motors. So does the V6 mazda 6S motor need 91 or is it just a waste?

I also know if the motor is supposed to use 91 and you use 87 it will throw on the "check engine" light, because the emissions sensor will read incorrectly if 87 is used. I'm currently using 91, but I really dont want to waste money if its not going to really matter.

Thanks!!!!!!!!
If the Owners Manual says that you don't need high octane than you don't. I Trust Mazda to know your engine better than anyone else. A car manufacturer wouldn't care if you used a higher octane because it isn't their money. Their only concern is that you get the most enjoyment out of your car.
 

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In my 2.5T I had been using 91 exclusively, trying Costco, Shell, and Chevron. Dealer supposedly filled up with Valero 91.

This last tank I tried Chevron 87. I'm just about ready for another fill up and I'm going to try Costco 91 again.

My observations:

Costco 91 seemed to drive fine. That was my first few fill ups after the dealer fill up was used (actually got 2 dealer fill ups).

Shell gas didn't seem to give me any improvements that I noticed, especially for the price difference. I only used one tank of 91, but it was so expensive and I didn't notice a difference so I probably won't use it again.

Chevron 91 seemed to drive better than Costco 91, but I can't be sure. There could have been other factors that made me think that, like cooler temps (finally cooling off in AZ), different driving circumstances to allow me to open it up more, etc. I used Chevron for the last few fill ups.

Chevron 87, didn't really notice a drop off in performance. However, it did seem to accelerate easier without spinning the tires. I'm wondering if it's pulling timing or doing something that produces less power down low. Or it's just placebo! :) It just seemed like it was easier to accelerate smoother with 87. With 91, I always seem to over accelerate and then overcompensate and let off the gas too much. I guess it seemed easier to feather the throttle with 87. With my next tank of 91 from Costco, I'll be able to see the difference with both brand and octane. It's possible I'm just getting more used to the throttle response and getting better with accelerating.

None if this is scientific and I fully admit some of the differences could be placebo or other circumstances. I'm going to try the Costco 91 again for a while to see if I can notice another difference between it and Chevron. And then if I'm happy with Costco 91, I'll try Costco 87 to see if the 91 is worth it for my driving style.

My driving is 90%+ local city driving on streets with a speed limit of 45, so I rarely am able to get it up in the rev range to probably even fully use the 91 octane. I'm ok with paying extra for 91 if it really makes a noticeable difference when I need it the few times I'm on the freeway.
 

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Our mechanic pointed us away from Costco Premium, towards Chevron Premium. Now, I have decades of auto experience as a wrench professionally (and I'm done with it) as well as personal stuff, so I thought "well, why not" as I'd never run Chevron before. Either it will make a difference or it won't....and it sure did. HUGE difference in performance in our Passat 1.8turbo. Having said that, I've also tried Shell V power and Texaco Premium (owned by Chevron and with Techroline)...any of the 3 I have found better ...FAR better than Costco Premium. YMMV. For me, I'm generally buying Shell or Texaco right now as the Chevron is the most pricey, but IMO the BEST performer of them all hands down. Even my wife notices the difference. All three give far better results in our car than Costco's "top tier" fuel. If I'm not pinching pennies it's Chevron as my #1 pick without hesitation.

In short, no more Costco gasoline for us..in spite of the fact I've been a Costco member for over 30 years. YMMV, IMO, etc.
 

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This is just one of those arguments that will boil down to personal experience. Science or fact be damned. Personally, I use Chevron 89 and the car runs exactly as expected. Why 89? Mostly because of the higher compression ratio of the SkyActiv engine. I have ran 87 in it before and while it runs perfectly fine it does seem to idle just slightly rougher. Didn't see any benefit of running 91 or higher versus 89. This could be my imagination, who knows.


Bottom line is to make sure you're using a Tier 1 gas formula. So stick with the major brands. That local or discount gas might cost you in the long run.
 

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Our mechanic pointed us away from Costco Premium, towards Chevron Premium. Now, I have decades of auto experience as a wrench professionally (and I'm done with it) as well as personal stuff, so I thought "well, why not" as I'd never run Chevron before. Either it will make a difference or it won't....and it sure did. HUGE difference in performance in our Passat 1.8turbo. Having said that, I've also tried Shell V power and Texaco Premium (owned by Chevron and with Techroline)...any of the 3 I have found better ...FAR better than Costco Premium. YMMV. For me, I'm generally buying Shell or Texaco right now as the Chevron is the most pricey, but IMO the BEST performer of them all hands down. Even my wife notices the difference. All three give far better results in our car than Costco's "top tier" fuel. If I'm not pinching pennies it's Chevron as my #1 pick without hesitation.

In short, no more Costco gasoline for us..in spite of the fact I've been a Costco member for over 30 years. YMMV, IMO, etc.
Thanks for the feedback. I think that's what my little "experiment" is proving out for me, too. Now I'm trying to figure out if I even want to put in another tank of Costco. I've been with Costco a long time as well, and normally their products are top quality. But gas might be a different case.

This is just one of those arguments that will boil down to personal experience. Science or fact be damned. Personally, I use Chevron 89 and the car runs exactly as expected. Why 89? Mostly because of the higher compression ratio of the SkyActiv engine. I have ran 87 in it before and while it runs perfectly fine it does seem to idle just slightly rougher. Didn't see any benefit of running 91 or higher versus 89. This could be my imagination, who knows.


Bottom line is to make sure you're using a Tier 1 gas formula. So stick with the major brands. That local or discount gas might cost you in the long run.
That's the thing, Costco is supposed to be a top tier gas. So technically, it should be just as good. But maybe their additive, while keeping the engine clean, hinders performance. Maybe I'll have to experiment with 89. But I figure, if I'm going up to 89, why not just go all the way to 91! :)
 

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Just to throw in my $.02, around here there's almost always just the two choices, 87 and 91. 91 is usually about 50 cents more per gallon, so there's absolutely no way to justify the added cost (over a year it would be SUBSTANTIAL) when you're not running a performance engine that requires higher octane. I try to use Top Tier stations, but if not it's not a big deal. In my 20+ years of driving, I've never had a single issue that could be attributed to anything fuel-related. I've never owned a turbo engine either, so take that with a grain of salt.
 
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