Yes, I know I bought a sports car and as such I can not and do not expect Honda Insight level MPG.

Yes, I do have a lead foot. I've owned a 1st gen RX-7 and 4 Miatas and have driven the heck out of all of them. Yet, I consistently got very good fuel mileage.

With only 1500 miles on the car I took a road trip from Atlanta to Cary, NC and at that time averaged about 18MPG on the highway. During around town driving I was getting 12-13MPG, which was expected until the car is thoroughly broken in.

I now have nearly 6K miles on the car and my MPG has dropped to a completely unacceptable 8-10MPG.

No, I do not have some super scientific method of calculating my MPG. I do however average about 140 t0 150 miles before my low fuel indicator light comes on. When I fill up at the gas station, I typically put in just under 15 gallons in the tank.

No, I can not accept 8-10MPG from my RX-8. I took my car to the dealer almost three weeks ago, at which time they did the 'M' flash. A flash, I was told by the dealer, my car should have already had before I left the lot the first time, apparently not! I drove through a few full tanks of gas and saw no noticeable improvement. Now I am back to a measely 8-10MPG. I took my car back to the dealer again this past week. This time they found nothing wrong. No leak, No evaporation, Nothing. The service writer did suggest I run 87 octane, which he had heard improves MPG. I've read that here on the forum as well, but until I see that in writing from Mazda, I ain't gonna do it.

I spoke with a well respected gentleman here in town who also owns an RX-8 and a Mazda speciality repair shop, he could not believe the kind of mileage I'm getting. He stated that due to the 10:1 compression of the rotary he wouldn't dream of running anything less than the highest octane.

I'm at a bit of a loss as to what to do next. The service writer is supposed to be getting back to me after speaking to his shop foreman for more input. In the mean time I'm calling other Mazda service departments to get their thoughts on the matter.

Anyone else experiencing MPG this low? For your sake, I hope not! Sorry, I know everyone must be getting tired of posts on MPG!

Yes, I still love my RX-8!

 

Ask you dealer to pull you plugs or make sure both of them are firing unless your on a road course 8-10 shouldn't be caused by anything "normal"... MAF variance or not.

 

how fast were you driving when you went on the road trip that you got 18mpg? did you travel most/all of the highways in 6th gear? cruise control on?

also when you say "just under 15 gallons" what does that mean? every time i fill my tank i put in 13.5 gallons give or take a tenth.

 

I believe I averaged about 70 mph on my road trip. Traffic is fairly heavy in areas and there was a lot of construction as well. Yes, I did use 6th gear quite a bit. I have no issues with the 18mpg times, especially not while still breaking in the engine and getting used to driving the 8.

"Just under 15 gallons" means that I might put in anywhere from 14.5 to 15 gallons when filling up. I typically try to fill up before getting that low, but I do recall a couple times recently when I've put in over 14.5 gallons. I just filled up about an hour ago and put in 13.967 gallons and had 141.7 miles on the trip odometer (happen to have my receipt in my pocket).

 

Even your 18mpg road trip suct. It's gotta be something wrong. Take it to another mazda dealership and have them look at it if your regular place is throwing in the towel. Keep on it, cuz your mpg is way way too low!!!!!!

 

Gotta agree here, if the plugs arent firing properly, you're gonna be wasting a lot of gas.

 

Yes, I would agree with that as well. The service record does state that they drove the car and monitored the conditions of fuel useage at idle and while in motion. Had the plugs not been firing I'm fairly confident they would have caught it.

However, I may be naive in believing they really ran all the diagnostics they claim to have. Pending the more indepth response from the current dealership, I may be going to another one. I've already placed a call to another dealership that is going to have their resident rotary guy call me on Monday.

 

The sooner the better. Naive or not, you just need to get somebody - anybody - to find & fix it. To wait for a miracle or something is just to prolong this miserable situation that you are in.

 

Calculating gas mileage is NOT some scientific marvel, it's basic math! However, without exact records, you hurt your case with the dealer. If you could go in and show "With this fill, I did 142.7 miles and it took 14.9 gallons" (and see, that's 142.7 / 14.9 = 9.6 mpg - very easy, right?)

Write down how far you travel between each fill - use the trip odometer, reset it when you refuel. Write down how much fuel you fill. That's all - but just the records from 3 or 4 fills will be enough proof for Mazda that something is wrong. Without actual records, it's harder to make your case.

PS - ask them to consider a catalytic converter problem?

Regards,
Gordon

 

ok i got 23.7 mpg driving with the cruise set at 80 6th gear climbing up into the mountains. 18 purely highway at 70 in 6th is NOT GOOD. there almost has to be something wrong.

also that last tank were you got 10.xx mpg is really bad. i spent the last period of time between fillups playing with the power in the car to see how bad the gas mileage would be and kept at 5k rpm and above for probably 80% of the time. i still got 15.x mpg. you do shift dont you?

 

You might want to check your tire pressure.

 

Good point Gordon. Gotta collect that data!

I write down my total miles (not really needed, but...) and my trip miles on my reciept. Then I reset the trip odometer. (The reciept always has the gallons printed-out on there.)

Then at home, (after entering the debit card charge to my checkbook) I go to my excel program and enter the date, total miles, trip miles, gallons, price & fuel type (like "Amoco premium" - my favorite), then throw the receipt in the trash.

The program calculates mpg & charts it.
It also calculates the overall avg mpg (18.4 presently, btw)
It also charts my total miles. (6,383)
It also calculates the avg miles per year. (6,209)
It also calculates price per gallon & charts it.

I also have a comments column where I add stuff like oil changes, reflashes, when I installed my CZ unit, when I removed my CZ unit, anything just for the record, especially if it could affect my mpg.

 

On several 234 mile trips freeway mileage in 6th with cruise set at 75 I'm getting 23.8xx, 23.9xx mpg. Filling up when the light comes on takes 13.xxx gallons. Around I'm getting 16 to 18 depending the revs I shift at.

 

Ok...

The tank is 15.9 gallons in size. I only use Shell V-power in my 8. She has had the M-flash. It's a manual and I drive like a rental!! Sometimes I baby it, sometimes I gotta hear the "beep"!! Mine also has 3k miles on it.

I get Hwy on avg 20 MPG, city 15 MPG. Approx 230 per tank.

I guess to only suggestion I can make is vary your fuel brand. Don't mess with Octane, stick to 93. Failing that call Mazda USA.........1-800-222-5500 and complain this should spark some detailed urgency with your dealer.

Good luck!!!!

- Irish
P.S. How much is 93 in Atlanta these days????

 

Check your gas. I had this happen to me over the last two weeks. Gas mileage went from 17-18 to 14-15. This week it is back up in the 17-18 range. The only change had for that last two week period was trying the Shell V-power high octane...since everyone on this board raved about it. All I can say is that after several tankful's from two different stations, I'm no longer using it. My problem, and yours, could have been a bad load of gas or something as the stations are switching to V-power (closest Shell still didn't have it last week).

 

Shell V-Power 93 knocked about 2MPG off of my VW GTI VR6.

I miss being in Atlanta, with QT stations everywhere. Some of the least expensive gas, and it always seemed to add 1MPG to any car. No kidding - I tracked it consistantly for months to make sure I wasn't imagining it.


Don't know, but here's an easy formula to approximate it, guaranteed accurate anywhere in the US:

CostOfGasWhereYouAre > CostOfGasInAtlanta

 

Your using Shell right? A while ago there was a problem with their gas which had too much sulfur in it. It eroded something with the fuel gauge which gave people faulty readings. I suppose its possible you got a bad batch of gas which messed up your fuel gauge. Make sure they check if its properly functioning at the dealership. Good luck!

 

Just finished filling my tank at 746 miles and my gas mileage for that tank full was just under 22 MPG (296 miles/13.5 gals). About 2/3 of the driving was highway at 65-80MPH, with a few runups to 8K or so revs on acceleration. This is obviously perfectly acceptable mileage and equal to or even better than my 4Runner gets. Will be checking the mileage average over time and will post another data point in the future. Larry

 

I run 87 religiously and have never had a single problem. In fact, my dealer insisted I run 87 and had several other service techs their backing him up. They said it runs much cleaner in the rotaries and if you run high octane, you risk heavy carbon deposit buildups...

 

If you drive From 59-64 miles an hour ( Borring, I know) and in the highest gear. You should be getting 320-340 a tank and thats with 70% freeway 30% city streets. I drive 20 miles to get to work. It is in the Dealerships Mazda Fast Facts book ([My RX8] MT-362) a tank and for the AT-382 a tank. If you are not getting at least 265 miles a tank, someting is really wrong with your 8. Sorry to hear that.

Ry

 

UMMM, doesn't high octain gas burn cleaner. And If you are a Rev Beeper you blow all that carbon out your tail pipe...ZOOM ZOOM!!!! Been RevBeeping my 79 rx7 (second Engine 1994) lost an Apex seal in 2003, putting in a rebuilt 13b 4 port Bridge port as we speak.

 

265 i wish. Mine has 1700 miles and still have not broken past 253 on a tank. I am useing 89 octane. When i used 93 i was getting no better then 213 miles per tank. I allways fill between 13.4 to 14.3 gals. I will go with 87 in my next tank to see what happens. Right now my 8 is giveing better gas mileage then my Wife's 3.0L Tribute, and my car is soo much fun.

 

I have to second the beeper notion. If you are a beeper it's safer to run the high stuff to avoid setting off the knock sensor. All the posts I've read allude to reduced performance from 87 (some just say reduced performance others have noted a slight knock above 7k)...I like performance and I blow the carbon out regularly.

I don't track my milage anymore (established 14 city and 23 highway) as it seems very consistent. I managed 10.2mpg once but I was really pushing the car.

 

I've got 6500 miles on mine, and I have a REALLY hard time getting anything other than about 220 (+ of - about 5) miles out of a tank (avg 13.5 -14 gallons/fillup) = 15.4 to 16.7 Mpg My personal best so far (long road trip w/ Cruise control) I got a 270 mile tank with a 14 gallon fillup = 19.3Mpg.

So, After 4 months and 6500 miles I've still never broken the 20Mpg mark. For what it's worth, my miles are about 80% city, 20% highway ...and I do have the "M Flash" I've also rounded off my figures to the nearest 1/10th for the sake of simplicity

 

what are the speeds and is it a lot of spirited Driving. No one is really mentioning their speeds.