loco4rx8

Weird, I've never seen 83 octane gas. Then again, I've never seen 91 octane, so I have to use 93. Is there a particular brand that sells 91 in the MD/VA area?

Ole Spiff

The very short commutes with a cold car would definitely explain the low mpg. When an engine is cold there isn't enough vacuum pressure in the intake manifold to properly pull the air/fuel mixture into the engine so engine designers use a "choke" which almost completely closes off the air intake. This allows more fuel to be pulled in to enrichen the mix so there will be combustion in the engine. As the engine warms up and air-flow/vacuum pressure increases, the choke is backed off until it's open again and normal air/fuel ratio is achieved.

During the "choke" time it's a very good idea to NOT gun the engine or drive hard until the engine properly warms up. Drive it easy until it warms up and you'll improve the gas mileage. However in short commutes like yours, and especially in cold climates, it may barely start to get warm by the time you arrive. You're going to get the worst gas mileage because the choke pretty much is on most of the time.

It might not be a bad idea to start the car and let it idle for about 5 minutes in the morning before you leave so the engine can get warm; although keep in mind you're getting zero miles per gallon while idling, so take that into account when figuring mpg. In your case a warm engine will perform noticably better and due to your situation you should see better mpg overall.

TheColonel

I know it's a different car and a totaly different engine but I currently have a '94 Integra. (Getting my RX-8 hopefully soon!) I've done alot of experimenting with trying to get more mileage. I generally average 25-32 mpg. (which is higher than it's supposed to! I should also mention I do have a SRI now but I found my technique worked when it was stock) I'm from NJ and do alot of highway driving. Supposedly in 5th gear my car acheives maximum efficency around 55-62 mph. I've found this to be false. When I do that, I get around the projected EPA mileage. However, when I fly at 80-90mpg [I meant Mph] and also take it out of gear and coast on long downhills I can get the mileage I do. I also never slam the gas. I've found it helps alot to ease into it.

CERAMICSEAL

Maniac, very well put.Very intelligent post.
Haze, I think you are absolutely correct : if the motor doesn't get to its proper operating temps you are wasting fuel. By the way there is no actual choke mechanism used on modern fuel injected vehicles, they just run in an enrichment mode until they warm up.
I would suggest that driving at 3 to 4 thousand rpms is not the optimum range for this vehicle with its port configuration and gearing. The Colonel may have a point.

TheColonel

Whoa... call me a n00b, but lower octanes yeild more power, maniac? So I should use the lowest I can w/o getting premature det?

MazdaManiac

iTrader: (3)

Correct.
Go with whatever the lowest manufacturer recommended octane rating is.
Octane rating, or AKI, is a measurement of how difficult it is to get an intake charge burning. The higher the number, the more energy it takes ofr the charge to autoignite from all sources. That includes the spark plug and flame front.

MP3Guy

Very true. An engine is like a horse. You gotta let it RUN!!! Seriously, constant driving in the way you describe is awful for an engine's life.

eclps0

This sucks, the highest gas mileage I have ever experienced was 18.9 with 100% highway driving from NJ-FL. I now drive like a grandma and only get 17 mpg and I have 9500 miles on the car.
Right now as I type this my car is at the dealer getting a fuel consumption test and ECU reflash and other stuff. I am sick and tired of getting 190-220 miles per tank. I travel about 60 miles a day back and fourth from school-home on Monday and Tuesday and the rest of the week about 100 miles a day. I cant afford filling up my tank 3 times a week.

TheColonel

Glad to hear I'm better off with a longer commute! Nothing like 40-60 minutes on I-287 everymorning... Such is the price of life in suburbia....

Ole Spiff

Just out of curiosity... are the majority of drivers getting bad mileage on the east coast or in cold climates? Seems like every time I read a post complaining about mileage they are back east. Could it be the gas, or the temperature that's making a difference? I went to Vegas a week ago and ran the whole way, just over 200 miles on 3/4 tank of gas (87 octane regular) and I was averaging anywhere from 75-90 miles per hour in some stretches where the traffic was moving along at that speed. Not the best speeds for mileage but I still did much better than what I'm reading from people on the east coast are getting.

Maybe we need a poll for this: where do the owners live who are getting the worst mileage?

pp13bnos

Well, I take the 7 mile comment back. Its right around 10 miles one way. Keep in mind, this is only when I'm driving it. Often my wife steals the car, and her commute is around 17+miles. Last tank of fuel was 15mpg.

Hopefully apexi will make a power-fc for our cars soon. CJ

labrat

Regularly get 22-23mpg around town with 95RON. It all comes down to driving style. You may think you're driving like a granny, but check the other cars when you pull away from the lights. The RX-8 is a performance car, and uses gas to perform.

LesPaul

I've got a 9 mile commute. Today it is snowing and 25 degrees. My 8 has 2,400 miles on it and I have never gottent better than 14 mpg, no matter how I drive it. This short commute theory fits my situation, but I find it hard to believe that it could make that much difference. Should't the engine be fully warmed in about five minutes, causing the choke (ECU) to back off? My commute takes about 25 minutes.

aussie77

I have to put another vote in for the 'short commute' theory.

When I first got the car, I was getting around 17-18 mpg with it. The first real 'road trip' which was almost 100% highway driving, I broke 20 mpg (abut 20.45 mpg) for the first time. My second 'road trip' got me over 23 mpg.

However, since the weather turned cold, my mpg to and from work has plummeted. I am now getting closer to 14-15 mpg driving to work. This latest tank looks to be the worst ever, as I don't think I will even break 200 miles before I need to refill. The difference? It has been colder lately. My commute to work is 3 miles, with a lot of time spent idling. The car doesn't warm up until I am almost there. Given my highway mpg on the last road trip, I can't think there is something wrong with the car, but simply that it is running rich due to the engine being cold, and since it is cold outside, it takes longer to warm up.

When I refill I will start letting the car idle for a while before I get going and see if that helps. I'm in Atlanta so it hasn't been 20 below or anything crazy, but certainly cold enough it seems to be making a difference.

selmeralto

I've posted before on this question as someone who has a short commute in city driving with 13-15 mpg. I'll be taking a highway trip soon and I'll be watching gas consumption very closely.

But my question is this: Did Mazda NEED to have made the A/F mixture so rich when cold?

I think Mazda has done a marvelous job in engineering this car so my inclination is to think they did what they thought is necessary in this regard.

Still, I wonder what others, who are more knowlegable than I in these matters, think.

success07

Same story here guys. 760mi. and my 8 is just over a month old and I'm averaging 15-16mpg in Columbus. To and from work is roughly 25 miles including a track to lunch and the gym afterwards. I'm still breaking the engine in so I haven't been hard on the gas whatsoever.

'ole spiff' does make a good point. A majority of us in the midwest and northeast are reporting the bad mpg. I am trying to be an optimist and say that the warmer weather (when it returns) will yield better mileage. I let it warm up in the morning and at night before the journey home but 15-16mpg is the best thus far.

I plan on getting my first oil change within the week and I planned from there to see what the redline was all about. Scared to think what the mpg results will be at that point. Regardless of the gas mileage, I am enjoying the heck out of this car.

RX-8 friend

Labrat, did you use US gallons to calculate your mileage or was it imperial? Got to watch that conversion. Wish everyone would just switch to metric litres per 100 km.

ptiemann

yes, they HAD to and that's why we lost 9(+?) horsepowers.

The richer mixture lets the cat. converter reach its operating temperature sooner.

Emission control requirements for 2004 required that.

Read this thread on the A/F mix

Maybe you want to leave a comment there so that it pops to the top again. It's important to read, IMO.

-Peter

selmeralto

I'm posting this note to pop it to the top for the benefit of others who might be interested in Peter's comments about the connection between HP, MPG, and emissions. Thanks, Peter.

klegg

on my 14 fill up. I am getting right around 18 mpg, BUT had one tank at 20, and one tank at 14mpg, no reason I can see for this. Strange.

Rotary Nut

Bumped for an update

brothervoodoo

..

mikeb

why do you have to convince dealer to flash ecu?

they flashed mine for cel reprogram and now its never come on again.

My mpg is roughly 17, I want mine flashed

Rx8Past

when do you think the dealer's will start flashing the ecu's?

brothervoodoo

Okay, let me clarify. There is procedure for CEL lights which is reflashing ECU. My car doesn't have any problems, no CEL flashing, etc..

I just want better mileage and was only thinking out loud. There is no evidence that reflashing ecu is going to improve gas mileage (but I'm not above trying it). There is currently no bulletin or whatever about indiscriminately reflashing ecu's...