I did that for a while

I got around 14 to 15l/100 ( 16 to 17mpg) while driving hard on the highway. By hard I mean 160kmh+ or around 5,000rpm.

In the city, driving hard I got 18-19l/100 (12-13mpg)

So, I decided to see if it is POSSIBLE on my car to get better than 18mpg.
So, I did the run at sub 4000rpm and WAS able to get just over 18mpg.

Other RX-s dont matter much as a comparison, IMHO.
On the Renesis we have there are 3 pairs of intake runners.
One runs 0 to 3750rpm, the second cuts in there, and at 7300rpm the 3rd pair cuts in.

Adn it seems very much like our fuel mileage is tied pretty predictably to how many intake runners gives you what mileage.

Again, as has been mentioned, ECU settings are likely the culprit.
Until we test with JSpec ECU maps, or other modded ones with leaner burn on higher RPMs we will not know with any certainty.

JDM getting soot?
 

Canz, you are the man: "Until we test with JSpec ECU maps, or other modded ones with leaner burn on higher RPMs we will not know with any certainty."


One question--are JDM cars getting the black soot on the tail pipes that we are getting here? It seems that the ECU programming that runs the car rich to "protect" the engine (as some speculate) would not be unique to the US cars. Of course, that says nothing of the programming (unfortunately apparently for us with the State-side smog-regs) designed to extend the CAT life.

Just wondering...my mileage and possible the performance too seems to be creeping up as I approach 2K miles on the odo. Though I have done a couple of long stretches (40+ miles) on the highway lately. Not without some second guessing, I sent my info for the buy back yesterday. But, as I still own, drive and appreciate much about the 8, I'm no troll...yet!

On that note, after dropping the paperwork at the Post Office to get the return receipt on my letter, I switched the DSC off (not all the way off) and proceeded to rip around a couple of corners (35+ MPH) and loved the tail hanging out!!! Of course, that made me want to run back to the post office. But, if all the stars allign and I get the next car I have in mind, I will hopefully not miss the 8.........................too much.

Thanks Silver8, it is good to know with certainty my gender!]

As for the soot: "Dunno"

I mentioned this because I read aout some people getting better mileage, but I am suspicious. Some people drive low rpm by habit, and probably are gettting much better mileage than me.
I don't "drive it like I stole it", but I do like to drive fairly hard.
When I test drive cars at dealers the salesmen comment on the way I drive. Some say nice things, some say littel , and I once had a guy say "Eeep" when I drifted around a corner, but overall I admit to some "play".

If I meant to "drive at 55" I would have bought a Prius.

And, if I wanted to get 12 mpg I would have bought a Mustang Cobra..

Surely there should be a place in between those two?

Anyway, more electronics play and dynoing this Saturday. We will start to apply some different settings on our little ECU over-ride wedge experiment and see what it runs like.

In any case I hope to have some news come the end of the weekend.. Not sure just what yet, but time will tell.

Reply to 7neverdies
 

Thanks for practical experience gained from driving and working on rotaries. The problem is, they were not RENESIS rotaries. Here's the engine designer talking, in a book Mazda published: The side-exhaust engine was an entirely new design, with new components. To us, it was as new as the first NSU-built prototypes.... And so were the problems and challenges with the new design, which were as numerous as they were unforeseen.
IMO, some lessons learned from previous models may still apply; others won't.
As for setting straight those of us who are disappointed with our gas mileage, I'm afraid you drove right off the road on that subject. We're not dimwits. We knew pre-RENESIS gas mileage was low. So did Mazda. Their book explains that Ford would not have allowed them to build the RX8 if Mazda hadn't proved it would be much better. And it was. The EPA-certified engine got 18-24 (25 for auto, which has lower revs and is higher geared). So we are not fools expecting more than we should have from old design engines. We're otherwise smart folks who trusted Mazda to deliver engines like the pre-production RENISIS, engines that perform up to spec. We bought the right car, but Mazda didn't deliver it. I'm still hoping that we can get Mazda to make our engines, as well as new production, do what they are designed to do.
What's baffling, and frustrating, is that Mazda won't tell us what went wrong. They knew all about durability concerns when they finalized design on engines that made 247/207 hp and good mileage. Why did they sell us ones that don't? My guess is that production quality, especially on seals, fell short. Mazda's book explains that the new, better seals allow higher pressures, bringing more power and better economy. But I'm just guessing.

Mitch

Watch out! I hear the "Yay Birds" coming..

They will vilify you and write bad poetry about you, and if you are VERY lucky they will start threads about you.

Please be gentle, their feelings are easily hurt.

Recent MPG approaching 2K
 

I've been getting 14 MPG consistantly in LA city driving. The only exception has been a 90 mile round trip with all freeway miles. For this non-stop I finally got 19 MPG.
I have 1800 on my 8.
The last full fill-up jumped to 16 MPG and all of my standard city driving.
Maybe there is something to the rumor of MPG improvement as you approach 2K.
I stopped using premium after my second $28 fill up. Regular unleaded seems to be fine.
I am keeping my 8.

Re: Reply to 7neverdies
 

Well said!

None of us bought the RX-8 expecting 30 MPG from a rotary or crystal clear exhaust from an engine that, by design, burns oil. Nor did we expect a Version 1.0 car to be bug free.

What is frustrating is that Mazda isn't saying anything at all on the low MPG and low dyno testing issues, which are much more than simple V1.0 bugs. It is like we are too stupid or too unimportant to deserve an explanation of even what the problem is.

Kind of like if Microsoft built cars ......

Yeah - its a shame when people jump on & pop out post #1 without so much as doing their homework.....

Anyways, my RX-8s 12-13MPG saga continues, unwavering - narry an improvement as I approach 2k miles. I have a sinking feeling 2k is gonna blow right by without any change. If, for some reason things get better, I'll certainly let y'all know.

On another note, I wanted to mention a question that MNAO asked me during the course of the initial buyback call I made to them. Others may have gotten the same question: "Why are you returning the car?" Of course I said the mileage was worse than a Ford Expedition - approaching that of an RV. Then, she asked: "What kind of mileage are you getting?" I told her. Then: "Have you asked your dealer about it?" Of course, I have asked the dealer & of course, they have no clue, so I told her that, too. I bet if we could get our hands on the % of people returning due to bad MPG, it would be the #1 reason. Of course, MNAO would be horrified if the buying public found that out.

I agree that to many/most people, the mpg issue is more important than hp. I read in another post a couple weeks ago here, MNAO had told someone "Some buyers have mentioned the mpg issue but we've received no complaints." Sounds like a real smokescreen to me.

I called their helpline yesterday. I'm keeping the car but I "officially" complained about the mpg. They did not ask me about it, but I brought it up myself. I have no idea if they are doing anything with my complaint; I asked the guy about that and he said a record of my comments was made. I got the impression he meant in my customer file, but hopefully they have a database of complaints they are compiling and this should be a key one. Has anyone else complained to MNAO about mileage?

You have to make noise about it, a lot of noise. Car companies tend to be hard of hearing. We've all heard the "We've haven't had any complaints about this... You are the first one..." before.

The MazdaSpeed Protege owners were having problems with hesitation and other fuel related issues with their cars. They kept making noise and contacting people at Mazda and now they are getting a reflash that not only seems to have fixed their problems, but they ended up now with a nice power and torque boost. It helped that some Mazda employees owned the car and experienced the problem thenselves, but the involvement and the noise and calling the right people, not just customer service, is what did it.

my mpg was around 12 and it sounds crazy but others will agree once I hit 2k my mpg has approved to 18-19
As far as making noise--I would be

20 MPG - and less than 400 miles on odo
 

So far I have put gas in twice since getting my RX-8 last week. The first time I filled up (Citgo 91 octane), drove 131.1 miles and it took 8.6 gallans= 15.24 mpg. I then drove 126.4 miles and it took 6.3 gallons = 20.06 mpg. 90% of my driving is stop and go in the Tampa Bay area of Florida. The A/C is on all the time, The DSC has been turned off, except for 30 miles while it was raining. The car has less than 400 miles on it so it is not yet broken in and I have not gone over 6k rpms. I do not drive it like an old lady either. My previous car was a Celica GT-S and it had less torque than the '8' so perhaps I have been conditioned to drive differently, thus getting good mpg? (ps I averaged 27 mpg in the Celica)

I Finally Did It!
 

Well, I'm happy to report that I finally achieved the 24 MPG (as advertised) in highway driving. In fact I did it on 2 tanks of gas on a trip to Virginia. It possibly could have been better, except that road construction put traffic at a standstill for some time.

I have about 5,200 miles on my car now and I have gotten between 18 and 24 mpg on every tank (except on my track days at VIR which averaged 11.5 mpg). None of my driving involves a lot of city driving, though, which helps quite a bit.

Re: I Finally Did It!
 

Way to go, Kurt. I've been getting around 18 mpg since going over 2000 miles (I'm at 3800 now). any hiway driving is still pretty short-range around the San Diego area. Then I took a trip to LA and back and got 20.4 mpg; 80 percent hiway mostly with a/c running. Maybe that's the best I'll ever get; i dunno.

I can tell right now the tank I'm on is going to be maybe the worst ever and I don't know why. This is my first tank since the LA trip and I'm barely gonna get 200 miles before hitting E. I normally get 220 miles per tank; 240 on a good tank; 270 on the LA trip. Why would it suddenly plummet like that? No freakin' idea.

(BTW, I properly set the odometer and measure gallons at fillup to calculate mpg. I'm just using the mpt as a broad comparison.)

17.1 MPG. Just went over 3000 miles on this current tank.

Ive got 4300 miles and I hit 20mpg this tank

22mpg last tank, mostly highway, dsc/tcs on, several (6 - 8) sprints to 90 mph.. one to 110, and about 5 redline runs in 1st and 2nd.

900 miles on the car so far.. redlines were the ceremonial i just passed the 600 mile break in. :)

A/C was on half the time, and the car pulls very very well. (seemingly better every day than the day before)

Oh yeah.. I'm running premium gas.

Couple of ideas: RPM vs mileage. I've noticed in my 7 that I get worse mileage if I lug the car in a lower gear vs. rev it. Seems that mileage is more related to throttle position (when the secondaries open). Just throwing out a theory - the ECU probably runs richer when you lug it to avoid detonation.

Second: Can the ECU be reset? On a '7' the ECU 'learns' as time goes on and may not be accounting for your now changed driving style. On a 7 you disconnect the battery and press the brake down for 5s to reset it. Very noticeable when this is done as performance drops dramatically until it 'learns' again. Does anyone have an 8 shop manual to determine how to reset the ECU?

I thought you just disconnect negative on battery for ten minutes to reset ecu

That works too. Done it several times:D

What's guy, i'm getting the same out come with my 8. normal driving back and to from work. i travel about 15 miles a day and have to put gas in every 3rd day. so, yes the gas mileage sucks, but i still love the car. i traded my 91 300zx n/a for it. not totaly happy!

Hello all,

Wow 160 some replys on this topic, maybe there is a problem :)

Im getting about 14 MPG or less with about 600 miles on the car, i'm filling up every other day with 91 Octane. The problem HAS to be a mixture problem because not only is the exhaust tips BLACK the whole back of my car is coated every day with a layer of black soot. Yes they(mazda) says the car will run rich durring breakin but good god i'v must have at least 4-5 MPG of lost economy on the back of my car every day. The question is to all you 20+ people do you have the same soot problem? My soot covers from the trunk/window meeting back. I dont know if this PIG rich mixture is normal for rotery breakin but it just seems to be a bit much to me.

Keep this post going lets find a solution to this problem, no reason to get rid of this beautiful car :)

T o n Y

Tony, you've sure got the soot bad. I get it on the tailpipes immediately after washing I see new accumulation. But not all over the back of the car... holy smoke (so to speak!) I been getting around 17 mpg locally hiway/city; i think my current tank close to 15 but I'm due for fillup now to double check. We do have to figger this out and I'm sure there's a fix but we gotta get mazda's attention and help and right now they're keeping their head in the sand. Very discouraging. If not for that, I rate this car a 10 but I hate the crappy mpg.

Milage
 

I haven't used a calculator, but a quick crunch in my head says I'm getting about 10mph. I'll be honest though, I didn't get the car to ease up to speed from a light. I've been driving it like it's been begging to be driven.

I wish the milage was better. But whatever. Iraq needs to kick up some thanks soon anyway.

I got my 8 (6speed) 5 days ago, boy this baby eats fuel like a pig on a mission. Here's a ballpark figure, 17gl / 360 miles = 21.1 MPG. But 85% of them are highway. I hardly push RMP over 5k...just imagine what kinda MPG will I get if I was gonna have some fun with this baby. I guess 8 is like a high maintenance girlfriend, she's SEXY, she's HOT, She's FAST...but you need money to keep her around!!

Here's an interesting statement from the window sticker,
Results reported to EPA indicate that the majority of vehicles with these estimates will achieve between 15 and 21 mpg in the city, and between 20 and 28 mpg on the highway 28? Has anyone came close to 24mpg?

It's a bad idea to run the tank to near empty level. Car manufacturers recommended to refill the tank when it's down to 1/4 tank. This way, less deposits would get into your engine. Just a FYI.