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.
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.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 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.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.
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!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.