Got 29.3 mpg today
 

Just goes to show it is possible to get decent mpg. I got 29.33 mpg on a highway drive yesterday. 176 miles on exactly 6 gallons of premium.

Just changed the spark plugs
reset the ecu before leaving
Highway trip on fairly flat terrain
Cruise control at 74mph the whole way
No significant winds or tailgating


Anyone else ever gotten 28mpg+ or did I just get lucky :ylsuper:?

curious, but how did you measure exactly 6 gallons in the tank.

To be honest, I'm doubtful it's accurate. How did you measure?

Pulled it in right as the gas light came on on a level surface. drove till the gas light came on again. It was in series of highway driving too so I drove till it came on for 3 hours before it.

But even if it was +- half a gallon its still over 25.

clearly your profession isn't in a field of science, as assumptions aren't the best form of accuracy

yeah, that's why. You can't trust that


The gas tank is split in the middle, and you can trigger a low light with about +/- 2.5 gallons, with the excess or deficiency being on the other side of the middle hump.

I don't doubt that you got good healthy mileage, but I'd bet that you had ~1.5 gallons on the other side of the hump from the level sensor when you filled up.

You would have had to fill up to the top each time. And then you will still get variations from pump to pump in when they will actually trigger the cut-off. Calculations based on a partial tank fill is rarely accurate, and when it is, it's from happenstance, not from due diligence.

:scratchhe whaaatever, haters gona hate

Even at as much as 1.5 gallons (which would be highly unlikely since I wasnt winging hairpin turns throwing gas around) itd still be 23mpg at absolute minimum then.

We aren't hating. Really. We aren't.

Feel free to repeat that, only starting with a full tank, and then topping off again at 173 miles. Prove it.

You are going to see what we mean.

And for the record, I've had plenty of people discount me when I proved 22-24mpg tank after tank after tank. Again, I don't doubt that you got good mileage. Just not as high as you think.

Yup. That's why I guessed 1.5 gallons. It's totally normal top end for a healthy 8.

This is 8,330 miles in ~12 days on my 8. Note the return section in the bottom half at 75mph cruise.
https://www.rx8club.com/attachment.p...1&d=1285609880

Agreed, not hating, just doubtful.

I would say that you probably got a more believable number like 22mpg based on the driving conditions described.

I actually did one other time going from VA to NC and got 26mpg but that also included an 8 mile coast in neutral down i77. I really dont see where people get such low numbers as 15 and 13 mpg. maybe theirs was raced on track for a majority of its life?

No, you get better mileage cruising on the highway on the way home from a racetrack than you do on the way there. (typically) Carbon cleaning.

People getting that low of mileage are either A) not cruising, or B) have something wrong with their 8.

Wooooowww thats a lot of miles. but on the same note thats also at 80+.

Something I just considered is Ive been driving about 500 miles with a small trailer and a street bike on it, just detached it last weekend. I wonder if that had anything to do with it?

80+ isn't accurate :)

Well, it's not wrong, but the first digit needs to change. That's the first and last bit anyway. It's been over a year since those states, and with no warranty voiding issues now, it's not as big of a deal. The trip out to AZ we were regularly playing with 90-100. Wind resistance is HUGE as the speeds climb. Look at the trip back though, all in the low 20s for 75 cruise. And it really was 75 cruise. A million speed traps, so just left it on 75, which was sufficient for 65 or 70mph speed limits, cancel briefly in 65mph speed traps out of respect, pick back up after.

There are only two ways to measure exactly X gallons used.

1 is to pull the tank and drain it completely and add exactly X gallons, then run the car for a set distance. Pull the tank and measure how much is left. Subtract from original fill, and you'll have the amount of fuel used.

2 is to fill the tank all the way until gas starts to spill out of the filler tube. Drive a set distance, stop and fill past full until gas is spilling out again. Measure the volume of spilt gas and subtract it from the amount of gas put in. This will give you the amount of fuel used.

Your mileage is based of an estimate of 6 gallons used. That is why your figures have been questioned.

The normal way to do it is to top off your tank until the pump auto shuts off. Drive whatever distance, and top off until auto shutoff again. Divid miles driven by gallons paid for.

Curious, why would you put it in neutral? Wouldn't it be better to leave it in 6th and just not be on the throttle?

Wow, my last two tanks I ave 11.9 mpg,

Bren, out of curiousity, aren't you the dude that manual swapped a 4 port auto? If so, did you use the mt's rearend?

If you didn't, you will likely get better highway mileage than other mt's because of the lower rear gear.

For pure fuel efficiency, yes, no throttle 6th gear is better than neutral. However, if the slope isn't steep enough, the drag from the no-load engine in 6th is enough to prevent you from staying at highway speed, and can cause various issues with the vehicles around you, etc...

Awww what a buz kill, well I guess its impossible to know for sure now but it had to be at least above 23.
No I didnt do the swap, I considered it but found itd be just the same value to just sell it and buy a manual.
Yeah I couldnt leave it in gear or itd slow down.

I got 27.1 mpg in nice fall weather with slight wind behind me in my 07 6 spd auto on 2 different times.

I carefully filled it each time, but the refill was at the other station approx 290 miles away so there's some possible slight inaccuracy there with different nozzles and maybe slope of car.

Also, for mileage runs, I check my mail, then fillup with warm car.

If I fill the car the night before, I think the warmup would make it 27.0

Anybody measuring mileage without thinking of these things won't get the right data.

iirc gas cools the fuel pump so why let your gas get so low?

there have been a few others that good REAL highway numbers of 27-28 mpg. elara for one on a couple of occasions when new . i forget the others.

Best I've been able to do is 25 mpg on non-ethanol gas, but haven't had that impressive of numbers since GA switched over to ethanol blend full time.

OD has as well, but he has different gearing changes and FI that changes the whole game entirely.

I know there is discussion about running super lean for low load cruising. OD makes reference of it here: https://www.rx8club.com/series-i-engine-tuning-forum-63/bank-2-o2-sensor-affect-command-f-table-230104/ and notes that someone else is getting 28mpg running in the 15:1 AFR range, also FI though. Can't find the thread he referenced though.

Usually, spikes of good mpg are caused by underfilling on that single tank. What will happen then is your next tank will show below-average mpgs because you put in more than you started with. Sign up with fuelly.com and record over longer periods. Not many RX-8er's beat my mpg average over time.

Btw, better to be throttle off in gear than in neutral. In gear coast-down the fuel is completely shut off, neutral requires fuel to run.

This seems to make sense to me - but when I pulling the OBD2 data as I try this, the 6th gear coast down doesn't get nearly the mileage that a neutral coast does. By a factor of 3-5x, iirc.

Anybody else seen this? OBD2 fuel consumption data supporting neutral over "foot off pedal 6th gear coast"?

wow seeing all these high number is freaking crazy! I have a new engine bhr ignition new spark plugs new fuel pump and im still getting around 15-17 mpg :/ maybe an accessport will help..

ODB2 mileage data is theorized, not actual. The simple fact is that in neutral you are using a bit of fuel to keep the engine idling. If you are in gear with the revs higher than idle and do not have any throttle input, the ECU is not injecting any fuel at all. ODB2 mileage estimates are not really designed to account for this.

Low compression O2 sensor is failing, need transmission or diff fluid replaced, MAF sensor cleaned, etc... There is a laundry list of items that don't take much to kick you off the good mileage.

I have a ScanGauge 2 from my old car that I tried on my RX8 for a while but I yanked it out of the car cause I was tired of seeing my crap gas mileage. I never measured a full tank of gas cause I do a lot of short distance driving but I did look to see what I was getting as I drove. I know it's not 100% accurate but it gives you a pretty good idea.

City Driving: 12-15 mpg

Highway Driving: 17-25 mpg

Short Distance Driving: 5-8 mpg (not a fully warmed car/ couple mile driving)

There have been a few unique times on the highway where I would hit around 30 mpg at a speed of about 70 mph but it wouldn't stay there for long. I also noticed I got better gas mileage around town when I shifted at about 3500-4000 RPM. Kinda wierd but you gotta take those ScanGauge's with a grain of salt.

OBD2 data is calculated through a formula using MAF, AFR and VSS .... like RIWWP said, all theoretical.

series 2 transmission would help a lot too

It's the math: .1 mile / 0 gallons = ?? Any system doing "instantaneous" mpg calculations has to handle divide-by-zeros as an exception. What the programmers decide to show varies. Manufacturer, in car displays tend to be optimistic (duh). The Scangauge allows calibration of their unit to match the car being measured, but few bother to go through the trouble.

I have a Scangauge, which is accurately calibrated, confirmed by manual calculations. During the week my regular 25 mile commute is very consistent, so I know what is normal for my car, conditions, and driving style. On a bad day (cold weather, driving too fast) I get 21-22 mpg. On a good day (warm weather, staying under 70 mph) I get 27-28 mpg. And, everything in-between, depending...

Yesterday was a "good day" !

This one time at band camp.

Those are good numbers! But, in a real world, this doesn't cut it for 99% of us...lol

Post counts don't mean anything to 99% of us either. :dunno:

I don't know what you mean (not that it matters to me).

My driving is not in some imagined controlled environment. It is real world commuting: 8 miles city, 20 miles freeway, one-way. Ocean Blvd / 2nd St / 405 fwy / Sand Canyon Ave. Usually 1 redline before entering the freeway, when conditions allow.

I wouldn't worry too much about what others think about getting 29 mpg in your 8. If you are sure you did all the calculations correctly then you have done something many would like to achieve. They don't believe it because they don't want to.

You probably looked at the wrong trip meter...