HardHitter

Well, I tried doing a search for this, but I didn't seem to find anything too much on this octane. I've been running on 89 I believe ever since I got my 8. I was fine with it until the gas prices have been starting to sky rocket in Cali! I was wondering if dropping down to 87 would damage the engine or affect the performance at all of my 8. I don't have any engine mods at this time, so everything is basically stock. From what I've heard, people have got better MPG from dropping down.

RX4life

you are suppose to be runnin 91...

in General, i dont know y anyone would purchase an 8... VERY well knowing that it requires PREMIUM gas...if you can afford this car im pretty sure you can afford the extra few $$ to run the car "properly"



i dropped from 94 -91 octane and noticed that i got an extra 20-30 km a tank.. so to maximize value i fill up with 91 now.. since i didnt feel any gains in performance whatsoever with 94...IMO

BlueFrenzy

wrongo! The manual *suggests* 91 octane but says that other octanes are acceptable (as low as 87). There are many people who are using 87 octane without any trouble. The MPG will likely go up but there is a tradeoff in performance. Not a terribly noticiable difference if you are just doing regular driving and commuting. If the engine starts pinging or rattling then you're pre-detonating and should move up to higher octanes (and get it checked by dealer).

RX8CER

my sales told me run 91+

BlueFrenzy

HardHitter ... I'm not sure what you're using as your search keywords but I typed in "octane" and a zillion hits came up talking about this exact topic. Here's the one that's identical:

https://www.rx8club.com/showthread.p...ghlight=octane

shaolin

Geez...the difference is 20 cents/gallon. If you do the math that's 3 dollars per 15 gallons. Are you really that hard up on money? Eat at taco bell one less time every week and treat your car right for pete's sake.

HiTMaNN

i doubt your fuel mileage has anything to do with the type of gas. Where is the scientific part behind this its you just thinking its the gas :P

Xyntax

Nope, been using 87, 89, 91 since I've had the 8. I cycle through octanes but I mostly use 91. I just filled up with 87 tonight. Just make sure you don't use cheap gas stations coz I've had some bad idling with Rotten Robbie, AM/PM, Atco, Costco, etc. Also, I get less MPG out of those cheapo gas stations for some reason. I only use Chevron or Shell now, all octanes.

juikster

I don't think using a lower grade is going to kill the motor. But if you've got a heavy foot and like testing the limits more often than most then the higher grade would be the the more logical choice.

expo1

Amazing how many answers can be found in the owner’s manual, page 4-2 in this case.

Key lines “ Your Mazda will perform BEST with the fuel listed in the table” ( 91 Octane )

“You may USE a regular unleaded fuel with Octane rating from 87-90, BUT this will SLIGHTLY reduce performance”

Fuel UNDER 87 octane can cause problems according to the manual.

L8APEX

I second that suggestion. Don't buy the car, if you can't treat it properly.

SilverEIGHT

Is there anything not proper about this statement from the user manual?

MX6_2_RX8

Expo’s right. It is really amazing how much misinformation there is on octane in this forum.

The fact is that Mazda says it can be used with a slight loss of performance everything else is speculation and hypothesis. I can do that too:
People on this site have claimed that running lower octane will damage the engine over time because the knock sensor needs to see a knock before it retards the timing. This is true but this is probably true for any octane that is run. If 91 octane is run, the computer will advance the timing based on the fuel, air, temp, oxygen sensor and whatever else to maintain peak performance and the only way it can find the line is to step over it. I don’t know this but it sounds good. Don’t believe it because I don’t know what I am talking about.

Then there are those that say it is only 0.20/gal more, True but if you read the manual and thought you could use 87 and when you bought the car it was $1.85/gal AND you thought you would see close to the 24MPG because every other car you’ve owned you always get nearly the stated highway mileage…..Now, people are saying, well, you really should use premium and at today’s prices that is $2.55/gallon AND you are only getting 18MPG. Driving 12000 miles/year the difference is $750/year and significant for some. There have been many articles written, many linked to in this forum, that state that premium gas is only for premium attitudes.

Oh, and my salesman told me to run 91 too. He also told me the stock tires were run flat. Nuff said.

Now I will add my own misinformation. My car performs better when running 87 octane. I have tested it over and over with the trusty butt seat dyno.

Well, I’ve probably pissed off enough people. My point is that without real data, nobody knows. The real data says that 87 can be run without damage. Oh, the manual also recommends shifting at 3000 RPM. :D

ZimmR6

Well, slightly in his defense, if he's driving an automatic, i don't think performance matters much, so feel free to put in 87...the automatic is a pooch...

MTLbroker

I used 91 octane in the beginning but soon realized that I don't drive my car to the full potential anyways. Been using 87/89 octane for the better part of the last few months. I tell you, when stuck in traffic, there is absolutely no reduction in performance when using lower grade fuel. I haven't noticed any negative effects on the engine.

Aseras

actually a lower octane gas is more effiecient for power.

G8rboy

I wouldn't recommend it, living in a warm climate like you do... it doesn't take much detonation to ruin a rotary, and that seems like a good enough case not to use a low grade fuel just to save a couple bucks. I personally use 89 in the winter, but once temps start to reach the 70's like this week, I'm back to 93 octane until the fall again... it's just not worth the risk, and I don't want the overbearing PCM to retard timing and lose HP just because I skimped on fuel.

spork

There's a Chevron in downtown LA selling premium gas for $3.07.

Yippee! Luckily(?) most other places in LA/OC are like $2.70. Sigh. I was going to go for a road trip to the bay area but I realized it'd cost me $150-$200 in gas costs alone to do that. That's just absurd.

rotarygod

I have been running 87 octane (and synthetic oil!) in all of my rotaries for years. Nonturbo rotaries love low octane. Unless you have forced induction you don't need higher octane. It is a waste of money.

Why do people quote the owners manual ONLY when it is convenient to them? No one reads those things and even fewer people actually listen to them. Your manual also states to use ONLY Mazda certified parts, that means no aftermarket parts (exhausts, suspensions, intakes, etc), and to also have your car serviced by Mazda trained professionals. How many people breaks these rules. I've never seen anyone go to an outside mechanic and tell them that they can't work on their cars because the manual doesn't say they can or because it says that only Mazda people should do it. People buy aftermarket parts for their cars all the time yet no one says that shouldn't because the manual doesn't say they should.

The owners manual is a set of guidelines. It is not absolutes written in stone. It isn't a book of commandments. Just merely a suggestion. If you decide not to listen to it in cerain areas, it doesn't mean that your car will fall apart. Taking care of it is taking care of it. Don't take anything in there as an absolute. Save yourself the money and use low octane.

MX6_2_RX8

The rotery god as spoken, I will never worry about putting 87 in again.

(BTW, that isn't a jab, from your other posts I trust information that comes from you.)


Yes, now everybody shift from 3rd to 4th at 29mph.

thrustn

I always use 89 octane. I tried 87 in the past but the engine made a terrible rattle sound whenever I pushed it.

Tayninh

If we listen to the media we will all be paying $6 a gallon for the lowest octane. That will cause most SUVs ( Lincoln Nav) to just park. RXs or any car is going to be very expensive not to mention intestate trucking and airline fuel costs are going to have a dramatic impact on everyone. Hope this does not happen by summer as predicted but let's hope market conditions will drive the price down. Perhaps we could start new oil wells in NJ.

EyeBall Fixer...(o)(x)

Very good point(s).... Thats why you are the rotaryGod!

RX4life

first i did notice the extra mileage ( a mere 20-30kms) and second.. 94 octane i believe burns 'quicker' for 'cleaner' performance in comparison with than 91 ... hence more gas needed for a certain set distance..

prove me wrong with your theory.. i was basing my assumptions purely from my understanding of octane ratings..

Brice-RX8

Actually the higher the octane the slower the burn which is why it is less prone to detonation it doesn't ignite as quickly. As far as gas mileage based on octane, I have noticed better mileage before using 89 over 93, but it might have been my head telling me not to push the car as hard because it had lower octane gas in it.