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rboerio 07-28-2004 09:23 PM

Cumulative Gas Mileage (Gas MPG) Thread
 
:( OK heres my theory, anyone who thinks that this is a logical possibility reply, elaborate, throw your 2 cents in.

*Let's say you were a car manufacturer and you released a new car(RX8). This is the first time the car has been designed and has a new engine design(Renesis). You offer a pretty good warranty -4 years, 48,000 miles. How can you release this car to the public, protect against warranty claims, and protect the engine's reputation, not to mention the car's and move forward smelling like a rose?

Answer: Program the computer in the car to run exceptionally rich through break-in period, this would help lubricate the engine(protect your new design). The car would obviously have bad gas mileage. If customer complaints are received, have the car taken back to the dealer for a "flash" to "update" the computer to help the problem-slightly. If no complaints are received, the programming of the computer would follow its course to run rich until a designated time, let's say possibly 5,000 miles or so then goes lean, OR throughout miles driven the car runs leaner and leaner until it is at its optimum setting(stickered gas mileage).

*Now I have seen several posts that people with higher miles on their car seem to get better gas mileage. From experience with mine, I am at 3,000 miles now-my mileage has gotten better than from day 1. I was lucky to get 11-12 mpg and now I'm getting 15-16. Ringing any bells yet? I do 100% city driving. If anyone should get the worst mileage it should be me.

*I am not an engineer, have no technical training on automobiles whatsoever-maybe this is far fetched -just using common sense and looking at the whole big picture here.

So.................what do you all think?

Oh yeah, I wish we had a formal document from MAZDA that told us what changes were being made to the computer with each flash-specifically. Rather than a TSB that is an answer to an "Engine Cranks, No Start" problem.

rx8cited 07-28-2004 09:35 PM

Theory does not hold for my car.

I have 10k miles (hit it just today .... I missed watching it roll over - darn) and my mileage has been consistently 19-20 mpg since day 1. My typical driving is 50 highway/50 city.

I calculate my mpg at every fill up, so I'm not doing any of that gas guage eyeball guestimating here.

rx8cited

rboerio 07-28-2004 10:00 PM

RX8CITED, when was your car built??

robertdot 07-28-2004 10:09 PM

I do too. I just hit 10K and and have been getting an average of 16MPG. However, I noticed that about 2,000 miles w/o NVRAM reset my mileage increased. But this was on a long haul from AL to CA, so any number of variables could have been introduced, especially less humid air and MUCH colder night air.

I don't know how long it takes before the '8 stops "learning" (if ever) and starts using the fuel trim settings. I haven't seen anything about it yet, but 2,000 miles seems as likely as any other number.

I'm not sure if that said anything important or not, but there it is for your consumption.

rx8cited 07-28-2004 10:19 PM


Originally Posted by rboerio
RX8CITED, when was your car built??

July 2003. I got the M-flash in April.

rx8cited

rodmeister 07-28-2004 10:20 PM

Whatever Mazda's reason, I appreciate the "M" flash. Before the flash I was getting about 15mpg in city driving, after the flash I', getting 18mpg.

khoney 07-28-2004 11:34 PM


Originally Posted by rx8cited
Theory does not hold for my car.

I have 10k miles (hit it just today .... I missed watching it roll over - darn) and my mileage has been consistently 19-20 mpg since day 1. My typical driving is 50 highway/50 city.

I calculate my mpg at every fill up, so I'm not doing any of that gas guage eyeball guestimating here.

rx8cited

Ditto for me on mileage, but I have 20K miles now.

Nubo 07-29-2004 03:17 AM

There was an extensive thread awhile back that collected member data and analyzed the contributing factors. As far as I can recall, mileage or vehicle age were not significant factors. The 2 significant factors were driving style and percentage of highway vs. city driving. IIRC, this was before the L or M flashes.

Tbone 11-15-2004 11:16 PM

2 cycles?
 
We're not talking about a 2 cycle engine here. Running it really rich isn't going to help the break in appreciably. A 2 cycle engine which is lubed by oil in it's fuel will benefit and require a rich break in. A 4 cycle or rotary would not. If anything, the car would "inject" more oil during the break in, or run the engine at a cooler temperature by limiting revs, or some other means. Those things would be important for break in.
Running more gas through it wouldn't. Make sense?

Xyntax 11-16-2004 12:10 AM

Nah, this MPG variance and "learning curve" for the ECU is just like Mazda's EPA excuse on the missing HP. They messed up on running too rich, that's all. Lean it out a little, problem is fixed.

Butch Brown 11-16-2004 06:56 AM

I have always gotten 19 - 23 mpg. I had less than a thousand miles on it and went PA to FL and back. 21 - 23 mpg on that trip. 21 at 85 mph 23 at 70 mph. At home I drive 35 miles to work, country roads 2 small mountains to cross, 3 stop singns and 2 traffic lights. I cheat by coasting down hills but I even did a sprint to 130 mph on one tank of gas 216 miles 10.271 gallons = 21.030084704507837601012559633921 mpg. Next tank no sprint 157 miles 7.408 gallons = 21.193304535637149028077753779698. I'm happy with that mielage. I push the throttle about 1/3rd of the way to the floor and shift in first and second about 6 - 7,000 rpms fourth about 5,000 then I often go right to sixth unless on a hill. it's amazing how fast the car is at 1/3 throttle if you just let it rev. I have always found with every vehicle I have owned the difference between 1/2 throttle and full throttle is about 10% more power for 100% more fuel consumption.

BRealistic 11-16-2004 09:49 AM


Originally Posted by Butch Brown
I have always gotten 19 - 23 mpg. I had less than a thousand miles on it and went PA to FL and back. 21 - 23 mpg on that trip. 21 at 85 mph 23 at 70 mph. At home I drive 35 miles to work, country roads 2 small mountains to cross, 3 stop singns and 2 traffic lights. I cheat by coasting down hills but I even did a sprint to 130 mph on one tank of gas 216 miles 10.271 gallons = 21.030084704507837601012559633921 mpg. Next tank no sprint 157 miles 7.408 gallons = 21.193304535637149028077753779698. I'm happy with that mielage. I push the throttle about 1/3rd of the way to the floor and shift in first and second about 6 - 7,000 rpms fourth about 5,000 then I often go right to sixth unless on a hill. it's amazing how fast the car is at 1/3 throttle if you just let it rev. I have always found with every vehicle I have owned the difference between 1/2 throttle and full throttle is about 10% more power for 100% more fuel consumption.

Interesting. I think the emissions testing is not done at full thottle, so when the auto manufacturers tune their timing/fuel maps for full thottle- they tune for the most (safe)power and not emissions or fuel economy.
>>>personally, I think driving style does make a difference, but not near as much as the vehicle itself and driving conditions. I have an 02 Tundra (reg cab V6 auto 2wd) and an 85 RX7 (GS five speed). They both get 15mpg in normal driving, though I 'normally' drive the RX7 harder than the Tundra. The Tundra is rated 16/19 by the EPA, but rela world conditions return 15mpg in town (pretty good for a truck of this size), and 15 on the interstate (sucks- because the engine has t work too hard). In contrast my coworker's new much heavier Sequoia 4x4 V8 get 13 mpg in town and 18mpg on the interstate. The only way I can increase the mileage is to drive on 50mph country byways for long trips (yawn). I have tried driving like grand pa for entire tanks- and I get maybe 1/2 a mile per gallon boost. :-/ The real issue seems to be how inadequate, outdated and rediculous the current EPA testing is for modern traffic conditions.
-Bryan

Dephender1 11-17-2004 01:01 AM

Poor Gas Mileage (12.5 mpg)
 
When I first got my RX-8, I was averaging approximately 15 miles per gallon (about what I would expect according to the documentation). However, I am approaching 5,000 miles and the fuel economy has taken a dive for the worse! On a full tank, I can only cover ~220 miles!! When I first got it, it was about 300 miles on a full tank. Not to mention, I don't drive with a lead foot or rev the Renesis high like its designed to. My daily driving is about 20 miles on the highway, not too much stop and go....

Items that I took into consideration:

1. underinflated tires (confirmed that they WERE underinflated, at 25psi :not flat enough for the pressure transmitter to pick up) but I resolved that issue, no improvement

2. fluids (had my oil changed) :after my oil change, i allowed the car to warm up for about 10 minutes with a completely full tank, distinctly above the F mark....after the ten minute duration, the gage was below the F!! So that invalidates the 'underinflated tire' theory...

3. dirty air filter (inspected and cleaned)

4. this may be far fetched, but I noticed that the fuel cap does not seal like older cars, could fuel be escaping as vapor?

Notes about the vehicle:

1. Its ECM has been reprogrammed

2. 6 speed manual ; so i would expect better fuel economy

Has anyone experienced this same problem and / or have suggestions to offer ? I would really apprecite it!!

P.S. I know its a sports car and fuel consumption rate is expected to be high, but 12.5 mpg is ludicrous! Full size domestic trucks get that kind of mileage! THANKS!

mysql101 11-17-2004 01:08 AM

220 miles / 13 gals = 17 mpg.

If you were doing 300 miles on a tank, thats 23 mpg...

I'd say you're currently getting normal mileage, and previously getting extraordinary mileage.

SantozRx8 11-17-2004 01:15 AM

isnt the tank 15.9 gallons not 13???

mysql101 11-17-2004 01:18 AM

yes, but my low fuel light comes on around 13. maybe it's different from yours.

mysql101 11-17-2004 01:19 AM

but even if he drained his tank of all 15.9 gallons of fuel, 220 miles would still be 13.8 mpg. :)

Dephender1 11-17-2004 01:35 AM

Jason,

I'm not sure I understand what you meant by your low fuel indicator light coming on at 13 gallons. According to the Owners manual, the capacity of the fuel tank is 15.9 gallons as SantozRx8 has stated. I am basing my calculations on the 15.9 gallon value. For future reference, when the low fuel indicator light comes on, that translates to approximately two gallons of fuel left in the tank. This is just a preventative setpoint in most automobiles to keep drivers from being stranded. But with the RX-8, when that light comes on, its like a race to the gas station! Aside from the speedometer and the tachometer, the Fuel gauge is very dynamic!! I watch that gage go down as the gas price goes up!!! yikes!! Thanks for the concerns and comments! And Santoz, thanks for the clarification! I'm sure we're all happy RX-8 owners, but that 12.5 mpg really does suck doesn't it?

Dephender1 11-17-2004 01:53 AM

By the way, I failed to mention that I DO have the revision M of the firmware in the ECM.

Thanks!
Tha

Mr M 11-17-2004 05:05 AM

The fuel gauge is only an indication of when you should fill up, not what your fuel economy is or how fast you are using gas.

Have you calculated your fuel economy by doing the below?

1) Fill the tank until the pump clicks off, then keep filling, the pump clicks off, then keep filling until the pump clicks off again.
2) Note your mileage, or reset your trip meter to 0.
3) Drive normally until the fuel gauge indicates 1/3 or less.
4) Fill up again the same way as before. Note how many gallons you have put in, and how many miles you have driven.
5) Divide the two and you have your mpg.

It sounds like you may be calculating your mileage the wrong way...

Let us know the results.

mysql101 11-17-2004 08:59 AM


Originally Posted by Dephender1
Jason,

I'm not sure I understand what you meant by your low fuel indicator light coming on at 13 gallons. According to the Owners manual, the capacity of the fuel tank is 15.9 gallons as SantozRx8 has stated. I am basing my calculations on the 15.9 gallon value.
...
but that 12.5 mpg really does suck doesn't it?

I used 13 gallons for my calculations because when the light goes on, I fill up, and add (usually) 13 gallons to the tank. So if my odo shows 220 miles, I take 220 div 13, and I get a 17 mpg.

As I said, even if you used 15.9 for the amount of fuel consumed (which is close to impossible due to the way the tank works), you still can't get 12.5 mpg if you drove 220 miles before filling up.

Clearly you are miscalculating your mileage. Your car sounds normal to me.

Sea Ray 11-17-2004 09:12 AM

Must be that new math I could never grasp :)

czr 11-17-2004 09:39 AM

You can not accurately guage mpg by only assuming how many gallons of gas filled up. Jason, even just 13 is not accurate.

To accurately guage your mpg. This is what you do:

On your next gas fill up, Reset your trip counter. Fill your car up completely, until the first "full" click.

After you decide to fill up again(I usually wait until lesss than 1/4 tank), go to the gas station and fill the tank completely again till the first click again. On the gas station pump it should have registered how much gas you have put in the tank. I think it measured to the thousands place. My last fill up was like 13.281 (empty light came on) and the trip odometer read 242.

Now divide the mileage on the trip counter by the last gas fill up. For example, mine was 242 miles/13.281 gallons = 18.22 mpg. 18.22 mpg mixed 50/50 city/hwy driving quite aggressively. tada

Edit: I usually use my cell phone to do the calculations at the gas station.

RXE16T 11-17-2004 09:43 AM


Originally Posted by czr
You can not accurately guage mpg by only assuming how many gallons of gas filled up. Jason, even just 13 is not accurate.

To accurately guage your mpg. This is what you do:

On your next gas fill up, Reset your trip counter. Fill your car up completely, until the first "full" click.

After you decide to fill up again(I usually wait until lesss than 1/4 tank), go to the gas station and fill the tank completely again till the first click again. On the gas station pump it should have registered how much gas you have put in the tank. I think it measured to the thousands place. My last fill up was like 13.281 (empty light came on) and the trip odometer read 242.

Now divide the mileage on the trip counter by the last gas fill up. For example, mine was 242 miles/13.281 gallons = 18.22 mpg. 18.22 mpg mixed 50/50 city/hwy driving quite aggressively. tada

Isn't that the same as Mr M's post two spots above you?

czr 11-17-2004 09:44 AM

Must have missed it. I wouldn't have bothered. My use of cell phone at the gas station to calculate the math is a good contribution though. ;)

RXE16T 11-17-2004 09:47 AM


Originally Posted by czr
My use of cell phone at the gas station

:eek: :eek: :eek: I hope it wasn't while you were pumping gas?

G8rboy 11-17-2004 09:47 AM


Originally Posted by Dephender1
Jason,

I'm not sure I understand what you meant by your low fuel indicator light coming on at 13 gallons. According to the Owners manual, the capacity of the fuel tank is 15.9 gallons as SantozRx8 has stated. I am basing my calculations on the 15.9 gallon value. For future reference, when the low fuel indicator light comes on, that translates to approximately two gallons of fuel left in the tank. This is just a preventative setpoint in most automobiles to keep drivers from being stranded. But with the RX-8, when that light comes on, its like a race to the gas station! Aside from the speedometer and the tachometer, the Fuel gauge is very dynamic!! I watch that gage go down as the gas price goes up!!! yikes!! Thanks for the concerns and comments! And Santoz, thanks for the clarification! I'm sure we're all happy RX-8 owners, but that 12.5 mpg really does suck doesn't it?

... but what does the pump indicate for amount of gas pumped in? That's the only number that's important. Unless you drive for a long time with the low fuel light on you're probably putting in just 13-13.5 gallons as Jason mentioned... so your mileage is in the 16's, which is normal. I've yet to put in more than 14.5 gallons, and in that instance I drove 35 miles with the light on trying to find a gas station.

G8rboy 11-17-2004 09:48 AM


Originally Posted by nojooc
:eek: :eek: :eek: I hope it wasn't while you were pumping gas?

You don't believe that myth, do you?

czr 11-17-2004 09:52 AM


Originally Posted by nojooc
:eek: :eek: :eek: I hope it wasn't while you were pumping gas?


How would you calculate the gas if you don't know how much gas you pumped in? So, of course it wasn't used while gas was still being pumped.

Also, using the calculator function would just be using the calculator at a gas station.

Also, no gas station has ever been proven to blow up by use of a cell phone. I don't know about other countries, but some states don't even have that law. :)

RXE16T 11-17-2004 09:53 AM


Originally Posted by G8rboy
You don't believe that myth, do you?

Not really.... I chat via bluetooth headset while filling up sometimes. :D

mysql101 11-17-2004 10:39 AM


Originally Posted by czr
You can not accurately guage mpg by only assuming how many gallons of gas filled up. Jason, even just 13 is not accurate.

No kidding.

This guy doesn't even get the basics on how to calculate mileage, what I mentioned is accurate - you just have to use real numbers, not an example number. There is no reason to complicate things when trying to explain basics to someone.

buzzwordenabled 11-26-2004 09:18 AM

Oxygenated Gasoline in the Northeast = Bad Mileage
 
Since they've made the seasonal switch to oxygenated gasoline, my mileage has utterly plummeted. Whereas my RX-8 previously averaged 20-25 stop-go/highway, I now see about 200 miles for the tankful. I've tried alternate brands including V-Power, but the seasonal oxygenated grade is the only thing available.

Has anyone else had a similar experience? My RX-8 has about 10,000 miles.

I can live with the seasonal lower MPG, but the reduced range is going to get me in trouble. :(

Howard 11-26-2004 04:37 PM

That could explain why my mileage went from 13mpg to 10.

Howard 11-26-2004 04:39 PM

By the way just what does oxygenated gasoline mean. How do they do that. maybe I could undo it.LOL

Doctorr 11-26-2004 05:00 PM

Oxycrap.....
 
The oil companies are forced to add alcohol to the gas, by state law.
In the corn belt, the farmers lobby mandates that ethanol from corn be added, but elsewhere it is usually MTBE (methyl tertiary butyl ether).

'Good' for the environment, but bad for your wallet and mileage. They can only put about 10% in, (it separates out if you put more) so your range shouldn't be reduced TOO drastically, sounds like it is more than just seasonal gas that is affecting your '8.....
.
.
.
doc

downshift 11-26-2004 05:31 PM

My mpg dropped from 17-19 to 15-16 (mostly city) over the last month or two. I think another contribution factor is extended warmup times. Are you idling too long when you're warming up the car?

mclarenracer22 11-27-2004 03:21 PM

I just got my RX-8, can you guys help?
 
Hey everybody!
I'm really startled in how much gas my RX-8 is wasting. It's brand new, got it off the dealer with 11 mi. It seems as if I'm getting around 220 to 240 mi. per tank. I have the auto version. Is that right?

expo1 11-27-2004 03:55 PM

“Wasting” in not really the correct term. Rotaries do not use fuel the same way piston motors do. Assuming you are putting in about 13 gallons at a fillup you’re getting over 18 MPG, which is not bad for this car. I get around 19-20 it’s just something you have to live with and has been covered to death on this board. If you have a few days to kill use the search feature for terms like “ MPG”, “Gas mileage”

poolsidenaz 11-27-2004 03:57 PM

I get 240 pretty consistently now - 6spd here.

RotaryNoob 11-27-2004 05:37 PM


Originally Posted by mclarenracer22
Hey everybody!
I'm really startled in how much gas my RX-8 is wasting. It's brand new, got it off the dealer with 11 mi. It seems as if I'm getting around 220 to 240 mi. per tank. I have the auto version. Is that right?


I got 220-240 on my first 2 tanks. Then I got the "M" flash and I can't do better than 180.

Charles R. Hill 11-27-2004 05:41 PM

With the "L" flash I was getting 23-24 mpg but the car only ran okay in the midrange rpm's. It didnt't really wake up until 6K. However, with the "M" flash it now gets 19-20 mpg but will easily tear the rear tires up if I am not careful. Of course, I have other mods but I think the new flash will benefit most everyone. I measured a 20 hp increase at the wheels with the M.

Charles

Dlrosie 11-27-2004 09:45 PM

I have an automatic. I consistantly get between 220 and 240 myself.

Omicron 11-27-2004 11:25 PM

RX-8 has a small fuel tank - that's what you're noticing.

Mikelikes2drive 11-28-2004 12:26 AM

i get about 180-190 if im lucky i get 200 -____-

w2aew 11-28-2004 09:24 PM


Originally Posted by mclarenracer22
Hey everybody!
I'm really startled in how much gas my RX-8 is wasting. It's brand new, got it off the dealer with 11 mi. It seems as if I'm getting around 220 to 240 mi. per tank. I have the auto version. Is that right?

Do yourself a favor and CALCULATE the mileage based on miles travelled and fuel consumed. A "tankful" is not a precise measure of fuel used, because some people fill up at the 1/4 mark, some at the 1.8 mark, etc. The ONLY way to compare your mileage with others is to do the math.

The tank holds about 15 gallons, but you don't run it down completely. Lets say that there's 3 gallons left when you fill up, this means that your getting 18.3 to 20.0 miles per gallon, which sounds just about right.

amartin 11-29-2004 11:25 AM

Gotta love it.. another gas milage thread... did a test..
 
I drove 170 miles @ ~80mph w/no AC, ambient temp was ~65 degrees outside.

Result: 18.9mph... thats 100% Highway w/no AC.

... I knew my car wouldn't break 20mph, I just knew it.

I am really wondering how some people are getting 18-20 in the city... you guys MUST be shifting at 3000rpms or something...

Or there's a lot of lemon RX-8's out there.

shaolin 11-29-2004 11:32 AM

Actually, I do shift at 3K RPM in the city when I'm just putting around town. I've done this in all my cars, and it always gets me the best MPG.

Gambit 11-29-2004 11:36 AM

i usually shift from 3k-4k just doing city driving and get about 17 mpg, but at higher speeds you'll get worse gas mileage...if you do your test again in the mid to high 60 mph range it should be better

dmp 11-29-2004 11:36 AM


Originally Posted by amartin
I drove 170 miles @ ~80mph w/no AC, ambient temp was ~65 degrees outside.

Result: 18.9mph... thats 100% Highway w/no AC.

... I knew my car wouldn't break 20mph, I just knew it.

I am really wondering how some people are getting 18-20 in the city... you guys MUST be shifting at 3000rpms or something...

Or there's a lot of lemon RX-8's out there.

I'd bet if you drove at 60mph, you'd get well over 20mpg. Your car can get better than 20mpg, IF the driver decides he/she wants to. :)

aggietiff28 11-29-2004 11:37 AM

Am cruising in 6th gear at 45mph or above. In 5th at 35mph, but I drive my car hard. Shift at 6000-7000rpm most of time unless just feeling gentle, then maybe at 4000rpm.


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