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Cumulative Gas Mileage (Gas MPG) Thread

Old 05-03-2017, 04:39 PM
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I just got my second RX8. My first one, years ago, (a bone-stock 2004 GT with about 80k miles) got a pretty steady 18mpg in mostly city driving. My "new" one (bone-stock 2007 GT with 42k miles) gets 14.5 - 15.5. Is there that much variation car-to-car?? I used non-ethanol 91 octane for a couple fill ups (the 14.5-ish readings). Now I'm using 89 octane and premixing and getting about 15-15.5.
I'm datalogging to dig into the causes and would like to post data and request information. It seems like I'm really rich under certain conditions, even though fuel trims look normal. It also burns my eyes to even get close to the car when it's running. But I need 29 more days and 9 more posts. Guess I'll just keep spending my whole paycheck on gas until then . Hope the cat lasts that long...
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Old 06-03-2017, 10:43 PM
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So desert racing I got 5 mpg
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Old 06-16-2017, 03:15 AM
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My Fuelly page for my S2 RX-8.

Averaging 14~15 MPG right now with premix. Not too bad IMO given how much I like revving it up.
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Old 07-18-2017, 09:10 AM
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2009 R3 61,000 miles (recently acquired)

First tank 60/40 city/hwy running 93 octane returned 15.75mpg
Second tank all city on 89 octane returned 14. 72mpg

Third tank i'm back to 93 to see what it will return without the benefit of hwy driving.

Fourth tank I'm going to ethanol free 90 octane
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Old 07-19-2017, 12:02 PM
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Be careful, you can do damage to your engine on lower than the minimum 91 octane that is recommnended. Lower octane use is really only for emergencies if 91 or higher is not available. Lower octane in these engines means poorer performance and greater chances of detonation., which can damage internal engine parts.

Last edited by gwilliams6; 07-20-2017 at 09:48 AM.
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Old 07-20-2017, 10:10 PM
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I've had my 2004 RX-8 automatic w/Touring Package for just over four years and 40,000 miles. 2/3 City. 1/3 Highway. I've tracked every drop of fuel (91 octane) that's gone in. Here are my averages to date:

Average MPG 16.7
Avg. city (est.) 15.9
Avg. hwy. (est.) 20.1
Best MPG 22.5
Worst MPG 10.5

Last edited by MotoKam; 07-20-2017 at 10:12 PM.
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Old 08-06-2017, 09:26 PM
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For my 2004 RX-8 6MT city/hwy mix (commute to work during the week) with non-ethanol 91 octane is 19/20 mpg. there is not much fun to be had in that commute. Weekends, which are more fun are more like 16 mpg.
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Old 08-23-2017, 07:27 PM
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I have a 2005 with an engine that has hot start issues - i usually get 16-18 mpg but i do mostly town driving. i used to be able to get roughly 20 on the freeway, but don't do that much anymore
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Old 09-27-2018, 08:08 PM
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2007 42000 miles 17mpg
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Old 09-28-2018, 07:14 AM
  #910  
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Originally Posted by semag View Post
I have a 2005 with an engine that has hot start issues - i usually get 16-18 mpg but i do mostly town driving. i used to be able to get roughly 20 on the freeway, but don't do that much anymore
...then you're getting excellent in town MPG with low compression!....
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Old 10-04-2018, 03:20 AM
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2005 AT 107k miles, 21 mpg, 60% highway, ran Costco Premium.
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Old 10-05-2018, 10:54 AM
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2004 at 95,518 miles. Mileage tracked since 47,612 miles in 4/2013. Factory rebuilt engine installed by Mazda dealer at 71,057 miles in 10/2015.

Overall Average: 16.7
City Average: 16.0
Highway Average: 20.4
Best: 25.9
Worst: 10.5

No significant change in mileage noted following new engine installation. 91 octane California fuel always used.

Cheers!
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Old 10-07-2018, 05:44 AM
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Well i used Castrol 2 stroke premix and went down to 13mpg from 17mpg with Amsoil weird ?
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Old 10-07-2018, 10:52 AM
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18-19 mixed city highway. Much bettr than i though but entire engine is refreshed
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Old 10-08-2018, 11:39 AM
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2007 Mazda RX-8 GT 6spd Manual
1,200 miles on Mazda Reman
Pennzoil 5w30 Platinum Synthetic oil
Lucas FD-rated 2-stroke pre-mix + SOHN injection
De-cat (due to visible cat damage)
Normalized compression results range [email protected]
Car is typically operated at ~7,000ft above sea level

Getting 18.5MPG mixed with a 40/60 city/highway drive cycle and five minute engine warm-up each morning. I shift normally between 4-6k RPM with frequent runs to 8-8.5k RPM during each drive cycle.

For comparison, here are the MPG figures of some of my previous cars, though most were owned at sea level.
1993 Jeep Cherokee Sport (automatic) - 16MPG mixed
2016 Mazda Miata Club (manual) - 34MPG mixed
2015 Fiat 500 Sport (manual) - 32MPG mixed
2009 BMW 335i M-Sport (manual) - 23MPG mixed
2008 Pontiac G8 GT (automatic) - 23MPG mixed
2008 Honda Civic Si (manual) - 25MPG mixed
1994 Mazda RX-7 (manual) - 19-22MPG mixed

Last edited by furansu; 10-08-2018 at 11:44 AM.
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Old 10-08-2018, 12:48 PM
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There is no need for a 5-minute warm-up unless your RX-8 is carburated. All you need is 10~15 seconds, then start driving gently.

I have personally started to try and stay at a lower RPM during flat ground cruising. Will report back after a couple of tanks.
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Old 10-08-2018, 03:01 PM
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Originally Posted by UnknownJinX View Post
There is no need for a 5-minute warm-up unless your RX-8 is carburated. All you need is 10~15 seconds, then start driving gently.

I have personally started to try and stay at a lower RPM during flat ground cruising. Will report back after a couple of tanks.
Eh, it has been really cold in the mornings which has driven the decision more than anything, I know the car will run fine skipping the wait. In the afternoons I take off after AWS finishes its run, so that is about 30 seconds to a minute.
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