Go Back  RX8Club.com > General Topics > New Member Forum
Reload this Page >

Cumulative Gas Mileage (Gas MPG) Thread

Notices
New Member Forum A place for new members to get their feet wet

Cumulative Gas Mileage (Gas MPG) Thread

Old 07-28-2004, 09:23 PM
  #1  
Registered User
Thread Starter
 
rboerio's Avatar
 
Join Date: Mar 2004
Posts: 33
Thanks: 0
Thanked 0 Times in 0 Posts
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.
rboerio is offline  
Old 07-28-2004, 09:35 PM
  #2  
Senior Member
 
Join Date: Jul 2003
Location: DC Metro Area, USA
Posts: 1,554
Thanks: 0
Thanked 0 Times in 0 Posts
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
rx8cited is offline  
Old 07-28-2004, 10:00 PM
  #3  
Registered User
Thread Starter
 
rboerio's Avatar
 
Join Date: Mar 2004
Posts: 33
Thanks: 0
Thanked 0 Times in 0 Posts
RX8CITED, when was your car built??
rboerio is offline  
Old 07-28-2004, 10:09 PM
  #4  
Registered
 
robertdot's Avatar
 
Join Date: May 2004
Location: BHM, AL
Posts: 1,071
Thanks: 0
Thanked 0 Times in 0 Posts
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.
robertdot is offline  
Old 07-28-2004, 10:19 PM
  #5  
Senior Member
 
Join Date: Jul 2003
Location: DC Metro Area, USA
Posts: 1,554
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by rboerio
RX8CITED, when was your car built??
July 2003. I got the M-flash in April.

rx8cited

Last edited by rx8cited; 07-28-2004 at 10:33 PM.
rx8cited is offline  
Old 07-28-2004, 10:20 PM
  #6  
Registered
 
Join Date: Aug 2003
Location: So Cal
Posts: 282
Thanks: 0
Thanked 0 Times in 0 Posts
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.
rodmeister is offline  
Old 07-28-2004, 11:34 PM
  #7  
FX8TED on my RX-8
 
khoney's Avatar
 
Join Date: Jul 2002
Location: San Antonio
Posts: 815
Thanks: 0
Thanked 0 Times in 0 Posts
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.
khoney is offline  
Old 07-29-2004, 03:17 AM
  #8  
Lubricious
 
Nubo's Avatar
 
Join Date: Oct 2003
Location: SF Bay Area, California
Posts: 3,423
Thanks: 0
Thanked 1 Time in 1 Post
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.
Nubo is offline  
Old 11-15-2004, 11:16 PM
  #9  
NW enthusiast
 
Tbone's Avatar
 
Join Date: Oct 2004
Location: SE Washington state
Posts: 89
Thanks: 0
Thanked 0 Times in 0 Posts
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?
Tbone is offline  
Old 11-16-2004, 12:10 AM
  #10  
THREAD KILLER
 
Xyntax's Avatar
 
Join Date: Sep 2003
Location: San Jose, California
Posts: 1,342
Thanks: 0
Thanked 0 Times in 0 Posts
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.
Xyntax is offline  
Old 11-16-2004, 06:56 AM
  #11  
Registered User
 
Butch Brown's Avatar
 
Join Date: Jun 2004
Location: Pillow, PA
Posts: 159
Thanks: 0
Thanked 0 Times in 0 Posts
Cool

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.

Last edited by Butch Brown; 11-16-2004 at 07:03 AM.
Butch Brown is offline  
Old 11-16-2004, 09:49 AM
  #12  
Registered User
 
Join Date: Aug 2003
Location: Morristown Tennessee
Posts: 140
Thanks: 0
Thanked 0 Times in 0 Posts
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
BRealistic is offline  
Old 11-17-2004, 01:01 AM
  #13  
Dephender1
 
Join Date: Sep 2004
Location: San Jose
Posts: 6
Thanks: 0
Thanked 0 Times in 0 Posts
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!
Dephender1 is offline  
Old 11-17-2004, 01:08 AM
  #14  
⎝⏠⏝⏠⎠
 
mysql101's Avatar
 
Join Date: Apr 2004
Location: USA
Posts: 8,623
Thanks: 0
Thanked 0 Times in 0 Posts
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.
mysql101 is offline  
Old 11-17-2004, 01:15 AM
  #15  
Raccoons SUCK!
 
SantozRx8's Avatar
 
Join Date: Jul 2004
Location: Jackson, Mississippi
Posts: 126
Thanks: 0
Thanked 0 Times in 0 Posts
isnt the tank 15.9 gallons not 13???
SantozRx8 is offline  
Old 11-17-2004, 01:18 AM
  #16  
⎝⏠⏝⏠⎠
 
mysql101's Avatar
 
Join Date: Apr 2004
Location: USA
Posts: 8,623
Thanks: 0
Thanked 0 Times in 0 Posts
yes, but my low fuel light comes on around 13. maybe it's different from yours.
mysql101 is offline  
Old 11-17-2004, 01:19 AM
  #17  
⎝⏠⏝⏠⎠
 
mysql101's Avatar
 
Join Date: Apr 2004
Location: USA
Posts: 8,623
Thanks: 0
Thanked 0 Times in 0 Posts
but even if he drained his tank of all 15.9 gallons of fuel, 220 miles would still be 13.8 mpg.
mysql101 is offline  
Old 11-17-2004, 01:35 AM
  #18  
Dephender1
 
Join Date: Sep 2004
Location: San Jose
Posts: 6
Thanks: 0
Thanked 0 Times in 0 Posts
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 is offline  
Old 11-17-2004, 01:53 AM
  #19  
Dephender1
 
Join Date: Sep 2004
Location: San Jose
Posts: 6
Thanks: 0
Thanked 0 Times in 0 Posts
By the way, I failed to mention that I DO have the revision M of the firmware in the ECM.

Thanks!
Tha
Dephender1 is offline  
Old 11-17-2004, 05:05 AM
  #20  
Evolution of REvolution
 
Mr M's Avatar
 
Join Date: Feb 2004
Location: Germany
Posts: 356
Thanks: 0
Thanked 0 Times in 0 Posts
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.
Mr M is offline  
Old 11-17-2004, 08:59 AM
  #21  
⎝⏠⏝⏠⎠
 
mysql101's Avatar
 
Join Date: Apr 2004
Location: USA
Posts: 8,623
Thanks: 0
Thanked 0 Times in 0 Posts
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.
mysql101 is offline  
Old 11-17-2004, 09:12 AM
  #22  
Registered User
 
Sea Ray's Avatar
 
Join Date: Nov 2003
Location: Nicholasville, Ky
Posts: 730
Thanks: 0
Thanked 0 Times in 0 Posts
Must be that new math I could never grasp
Sea Ray is offline  
Old 11-17-2004, 09:39 AM
  #23  
czr
RX8 RX8!
iTrader: (3)
 
czr's Avatar
 
Join Date: Aug 2004
Location: Tampa Bay, FL
Posts: 1,189
Thanks: 0
Thanked 0 Times in 0 Posts
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.

Last edited by czr; 11-17-2004 at 09:43 AM.
czr is offline  
Old 11-17-2004, 09:43 AM
  #24  
'RX-EIGHT'
 
RXE16T's Avatar
 
Join Date: Feb 2004
Posts: 2,768
Thanks: 0
Thanked 0 Times in 0 Posts
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?
RXE16T is offline  
Old 11-17-2004, 09:44 AM
  #25  
czr
RX8 RX8!
iTrader: (3)
 
czr's Avatar
 
Join Date: Aug 2004
Location: Tampa Bay, FL
Posts: 1,189
Thanks: 0
Thanked 0 Times in 0 Posts
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.
czr is offline  

Thread Tools
Search this Thread
Rate This Thread
Rate This Thread:

Quick Reply: Cumulative Gas Mileage (Gas MPG) Thread


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.