I have an '05 RX 8 6 speed...Like everyone else, mpg are not quite cool...about as good as a Ferrari Question....What will 89 Octane gas do to an RX8 over the long haul? I just couldn't find an answer on any of the forums and I know it must be out there.
Thanks

 

you'll get as many opinions as people who answer. i'm pragmatic.... the manual says 91/93 premium, so i have been and do for now. but however, i've thought about trying 87 or 89 just to see how it would run, and i've seen forums where guys say 87 and 89 will run just as well as 91 or 93. then i thought about it differently... i usually fill up at about 10 gallons at a time at todays local prices 3.89/regular....3.99/ midrange.... and 4.09/ premium, so the price spread for me is $38.90 to $40.90, 2 dollars times 1 fill up a week or 10 days, $2 dollars every week and a half. that's not even chump change, little more than the price of a cup of coffee. so right now it's not worth it to me to experiment with my own RX, but i'd like to on someone else's if you're willing. if the gas prices continue towards $5.00 or $7.00 as i've seen suggested, then i may think harder about at least alternating between 89 and 91 once in awhile, but not 2 or more tanks of regular in a row. i saw, but can't find it again, a comment in a forum that said some RX race drivers use regular grade because it gives better mileage, so fewer pit stops, but they rebuild their engines after ever race. i take that increased mileage claim with a grain of salt. i also remember when gas cost .20/.25 cents a gallon in 1962 and my two 4 barrel carbs. 389 Bonneville HD got 19 miles per gal.

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im a 20yr old college kid with a 04 6spd rx8 and ive been using 87 or just regular gas and ive seen no difference in the cars performance. i used to use premium gas but when the prices started getting up there i switched and honestly i think the rx8s can run on regular but still once in a while or every couple fill ups ill use premium

 

here in az we have 87, 89 and 91. i use 91 and sometimes 89. But as i've been told NEVER use 87. Something about what's in it will screw up the car. I only put 89 in when i have like less than 10 dollars and i just need to put some gas in it to get by. Other than that i ALWAYS put the highest grade in it. Everyone recommends not to go below it because of whatever additives are in the gas. We are sports cars or as mazda puts it "top of the line sports cars" you have put the highest grade fuel in it because of what's in it or the cars will screw up. You may not feel like it's bad but i'm sure in the long run it will screw up your car.

 

i will let you in on a pretty big secret here. if you get regular or mid-grade, you are generally getting the same thing. the octane rating is a minimum rating, not an exact, so what people generally do is get the same grade in the mid and regular grade tanks. it turns out cheaper that way since they don't have to have three different kinds of gas shipped. so that means, in the smaller stores, there are only two kinds of gas. the bigger stores will generally separate them, but the smaller stores usually won't.

 

well i'm not taking a chance from what i read the higher you go the more you reduce knocking in your engine and the longer it will last, if you continue to put in the lower grade it could ruin your engine.

 

Different octanes burn at different temperatures. Burn too cold, and deposits are left behind that you don't want (think extra deposits in the catalytic convertor), burn too hot, and you can damage linings/seals, and burn off deposits that can be beneficial.

Either way, you'll probably get different effects accumulated over time.

Why risk your motor for a few bucks? If you need to save a few extra bucks per fill-up, this is the wrong car for you, anyway.

 

it's not about me saving. I only take the mid grade if i ABOSLUTELY have to. Other than that i ALWAYS put in the highest grade I can go. I will not risk my car by going to the lowest grade like some are doing.

 

Umm, 'you' was being used in the most general sense of the word...

But the college kid up there might want to think about the fuel that's going in. Dude, if you need to save money on fuel by getting away from premium, I just don't think the RX-8 is the right choice for you. This car is thirsty as hell. And I know I wouldn't want to buy a used RX-8 if I knew the original owner was using regular...

 

oh i thought you meant you as in me since you replied after me. sorry about that.