Ok so 2 months ago I got my 04 rx8 with 80000km from a dealer. Bought extended warranty. I also bought new plugs, coils, wires, K&N drop in filter, cleaned MAF sensor and reset e-shaft with the 20 brake pedal trick. All that was done at 81000km.

Now I gave it some time that maybe the ECU needs to relearn fuel trims. But this is completely ridiculous im doing 300km per full to the top gas tank. I got 320km once and I was like woahhh.

Thats 185 miles per tank for you americans. My daily drive is 1km to the highway and 24km on the highway once I hit work. 5 days a week. I am not an agressive driver, I redline once or twice a day if not im always in the 3500rpm while cruising.

Im pretty sure there is def something wrong with the car. Any ideas? I mean 20L/100km is not anything near what mazda advertised. The car now has 83500km.

Im pretty sure the car was never seafoamed, would that be a solution? or improve mileage?

My leading plugs were black with brown crust around the tips and the trailing were the same but less black and more brown.

What could be wrong? I knew when I got the 8 it would be around 12-15L/100km not freakn 20.

What kind of fuel are you using?

I get about 230 a tank, maybe more if I drive extra conservatively.

But get a compression test done, your engine may be biting the dust?
idk

Same for me, I have a 2005 and I can easily do 400km from a full tank, and thats with very aggressive driving.

You definately have something wrong. Check your compression, maybe a seafoam wouldn't hurt.

What kind of fuel are you using?

I get about 230 a tank, maybe more if I drive extra conservatively.

But get a compression test done, your engine may be biting the dust?
idk


i always fill up petro canada super 94 with tecron or shell 91 when i cant get to a petro canada.

Same for me, I have a 2005 and I can easily do 400km from a full tank, and thats with very aggressive driving.

You definately have something wrong. Check your compression, maybe a seafoam wouldn't hurt.


hey PGROTHE if you know how to seafoam would you mind giving me a hand? ill compensate you for your troubles.

Could be a bad catalytic converter also...

I usually get 250 to a full tank on premium with average driving in the city

Buy the Cobb Access Port...

If you get it from MM you can get a better tune than the one they provide from cobb...

Retune the car to increase your MPG...its running pig rich from the factory for cat protection...

I have an 2004 with about 160K on it and do very similar type driving routine an a weekly basis. I regularly see ~350k to the low fuel light 400-430km to a fill up of 55 litres. Best mileage was 600k to a tank full on a long cruising drive. SeaFoam couldn't hurt but I don"t see it making the sort of changes you are looking for. Somethings up.

Hey there,
I live in Canada and my 8 just passed the ol' 90,000km marker. I cannot get more than 340km out of a tank, from full to when the light comes on. When the light does come on though, there is usually another 10 litres of gas left. This is ULTRA conservative driving. No heat, coasting to stops, 91, or 93 octane gas. The few guys I have talked to around here with 8's all have almost the exact same milage. The guys that are getting 400 and over amaze me, congratulations. I've also found that even when i drive half way agressive with rev matching and daily redlines, I will still get almost the same milage, mabye 5km less. I moniter my consumption pretty hardcore because I'm a student, I live on my own, and incredibly broke. :(

hey PGROTHE if you know how to seafoam would you mind giving me a hand? ill compensate you for your troubles.

I'm sorry I have no experience with sea foam, I would be happy to help though.
I've seen some video on this site that could help you too; there is a DIY for this too.

You live in Canada!!! It's winter right now, your fuel consumption will increase 20-30%! I haven't been driving my RX-8 in the cold that much, but my Prius went from 42mpg to 35mpg simply because the weather dropped to the 15-25F range (-10 or so C)

I am in the same boat, when I bought the car I was told 18mpg in the city and up to 24mpg highway. I went snowboarding on Monday, and did 220 miles with a full tank on the highway. I used cruise control all the way avg 70mph = 14.6 mpg on the highway :scratchhe

While it is true that our car is a thirsty one i think that complaining about your averages is pretty much useless because they clearly show that there's something to be looked at.
Start with the usual maintenance routine (spark plugs, coils, wires, fuel pump, injectors if your mileage is high etc) given that your engine is still running strong.
Worn out coils or spark plugs often make the fuel consumption fly sky high, so does a bad catalytic converter.

I usually get ~17mpg city, ~22mpg highway, and my cat failed (banging away at it all day to get a midpipe on before a trip tomorrow), and my mileage plummeted to ~9mpg.

Cat is definitely a possibility.

theres nothing wrong with his car, and if there is, the mileage will only improve slightly. That is the regular mileage of a car, and for the people who say they are getting 600, i don't know. It just sounds unbelievable that someones car could do 2x better than most people?

Oh well

theres nothing wrong with his car, and if there is, the mileage will only improve slightly. That is the regular mileage of a car, and for the people who say they are getting 600, i don't know. It just sounds unbelievable that someones car could do 2x better than most people?

Entirely possible. My mileage was cut in half from cat failure, so fixing it will double my mileage.

I usually get 300-330 miles per tank (~13 gallon fillup) all highway, 260-280 with city/highway mix. My last 2 tanks have been 140 miles and 110 miles with cat failure.

Health of the the entire powertrain matters a hell of alot more in our cars than most.

Yup surprise me too
Visiting family with the wife, Scarborough to Wiarton with a couple day's of local travel and back, low fuel light came on at 530km, Filled up with 60 litres technically I could have gone about another 30 or so before it would have cut out, but you don't want to stretch it too far you know:). Pretty much secondary highways 80-90kph. Amazed the heck out of me too. I'd done a 500km trip before but even those are very,very rare.
On a side note that engine just got replaced as of yesterday, sorry to see it go (15900km) still running smooth (low compression) , I hope the new one is as good.

theres nothing wrong with his car, and if there is, the mileage will only improve slightly. That is the regular mileage of a car, and for the people who say they are getting 600, i don't know. It just sounds unbelievable that someones car could do 2x better than most people?

Highway driving is a totally different world. I thought his original post was 1 km highway and 24 regular...owell

I believe the 04s were a bit more thirsty than than the years after.. But try cruising at 3k rpm. That about 40mph in 6th.

His first post says:

1km to the highway (city) and then 24 highway.

You live in Canada!!! It's winter right now, your fuel consumption will increase 20-30%! I haven't been driving my RX-8 in the cold that much, but my Prius went from 42mpg to 35mpg simply because the weather dropped to the 15-25F range (-10 or so C)

Meant to say winter will decrease your fuel consumption by 20-30%

your car is fine. thats about what im getting. just deal with it

I'd contend that your car is not in peak health either then.

Don't judge "fine" as being equal to your car, when better is clearly possible. True, he has the option of just "dealing with it", as you are, but he also has the option of working on it to restore the health of his 8.

Well, I have managed to get 175miles to the tank with my 09. This is like 10mpg. It has 500miles now. I hope to get better mpg, but am not complaining now because I know I am a little more spirited in this car for the time being. Redline, 100mph, of course after it warms up...


I do not drive this car everyday. When I do, it is because I want to. If i did have to drive it to work, I do not think I would fare any better. It is a short drive through more residential/city areas than not meaning stop and go. I have to go out of my way to hit the freeway which I do when I drive this car.

I knew coming in that this car is thirsty for fuel and oil. Right now I am thirsty for fun... I dont know who will give it first :evil_laug. I will drive normal on my next fill up to see what I get.

Another genius then, ever heard of break-in?

^ oh come on
with 500miles on the clock and a good warm up redline it the moon :yelrotflm

Your car will thank you in 30K when your compression has gone to shit.

Thanks... You all are right... It was just a couple of times... Feel really bad now and very silly. I will do better. Hard not to, but will pay in the end if i am careless now :( :( :( :( :( :( :(

Merry Christmas to me... :(

DAMN! I feel awful... I read on hear to redline it and the fun of the car, I was completely careless.. WHAT TO DO other that not do this anymore?

Ok so 2 months ago I got my 04 rx8 with 80000km from a dealer. Bought extended warranty. I also bought new plugs, coils, wires, K&N drop in filter, cleaned MAF sensor and reset e-shaft with the 20 brake pedal trick. All that was done at 81000km.

Now I gave it some time that maybe the ECU needs to relearn fuel trims. But this is completely ridiculous im doing 300km per full to the top gas tank. I got 320km once and I was like woahhh.

Thats 185 miles per tank for you americans. My daily drive is 1km to the highway and 24km on the highway once I hit work. 5 days a week. I am not an agressive driver, I redline once or twice a day if not im always in the 3500rpm while cruising.

Im pretty sure there is def something wrong with the car. Any ideas? I mean 20L/100km is not anything near what mazda advertised. The car now has 83500km.

Im pretty sure the car was never seafoamed, would that be a solution? or improve mileage?

My leading plugs were black with brown crust around the tips and the trailing were the same but less black and more brown.

What could be wrong? I knew when I got the 8 it would be around 12-15L/100km not freakn 20.

I'm in the same boat but 90% city/traffic, 10% hw. That was back in the summer.
I'm under 40k km and changed the plugs, still have to change the coils (bought them, still on a shelf).
Try seafoaming it, but I dont know if it's advised during winter :X

I'd contend that your car is not in peak health either then.

Don't judge "fine" as being equal to your car, when better is clearly possible. True, he has the option of just "dealing with it", as you are, but he also has the option of working on it to restore the health of his 8.

my car is just fine. oil changed every 3k on the dot. redlined at LEAST once everytime she's out. all recalls and whatnot done. new plugs coils and wires at 15k miles. im at 27k miles right now. never flooded. on and on and on...

that being said, my bad, i reread the original post and my situation is the opposite, i do 90% city driving. and the OP is matching my mileage. i get the average 20ish highway.

I believe the 04s were a bit more thirsty than than the years after.. But try cruising at 3k rpm. That about 40mph in 6th.

This is wrong.
3k rpm in 6th is around 60mph

thanks for the multiple replies guys!

Actually I like my car to be a peak performance and healthy at all times. For God's sake I wash her more than I wash myself! (hahaha joke obviously!)

I think I will bring it to the dealer after the holidays and force them to do something about it. Maybe the nasty smell that invades my garage after my 30 mins drive from work has something to do with my bad mileage. Kinda weird cause the new CAT dates from july 09. How can it fail so early... Unless mazda builds terrible quality car parts.

theres nothing wrong with his car, and if there is, the mileage will only improve slightly. That is the regular mileage of a car, and for the people who say they are getting 600, i don't know. It just sounds unbelievable that someones car could do 2x better than most people?

Well then you'll find this unbelievable as well...

I think there is something in addition to "inherent design characteristics" contributing to the poor fuel mileage, either driving habits, mechanical issues, or both. I have a 2009 with only 3,000 miles on it, so it may not even be fully broken in yet. Yet on my daily commute round-trip, which is 10 miles of city and 36 miles freeway, I am consistently getting 23-24 mpg. For the holiday I just drove freeways for 200 miles between 75-80 mph, and it used a little over half a tank, so obviously doing better than my usual commute. I'll know the exact figure when I fill up tomorrow.

The cars will definitely pull mid-20s mpg if they are mechanically sound and driven reasonably.
(keep in mind I'm quoting miles, not kilometers)

This is wrong.
3k rpm in 6th is around 60mph

That's with manual. With the automatic gear ratio, 3000 rpm in 6th is 90 mph.
:yesnod:

+1 for getting the cat looked at. Also, make sure the car had all its recalls/TSBs for ECU firmware reflashes.. the earlier ones run richer, apparently. I'm in Montreal also, my average fuel mileage in sig.. been tracking since about Oct. It's an 04 also. About 370km to the light, mixed highway/traffic. What speed are you going on the highway? I noticed you get about 24mpg at 100, but only like 18 at 130. I need to do more long highway trips to have enough stats, but over a couple of trips to Ottawa that's what it works out to.

thanks for the multiple replies guys!

Actually I like my car to be a peak performance and healthy at all times. For God's sake I wash her more than I wash myself! (hahaha joke obviously!)

I think I will bring it to the dealer after the holidays and force them to do something about it. Maybe the nasty smell that invades my garage after my 30 mins drive from work has something to do with my bad mileage. Kinda weird cause the new CAT dates from july 09. How can it fail so early... Unless mazda builds terrible quality car parts.


Yeah bad smells can be cat-related. Can you describe the smell? The cat itself is as reliable as any other car's cat, but in these cars if the coilpacks go, the amount of unburnt fuel going into the cat increases and the thing dies quickly, even a brand new cat. You said you had those things replaced? Make sure the work was actually done maybe.. who knows.

+1 for getting the cat looked at. Also, make sure the car had all its recalls/TSBs for ECU firmware reflashes.. the earlier ones run richer, apparently. I'm in Montreal also, my average fuel mileage in sig.. been tracking since about Oct. It's an 04 also. About 370km to the light, mixed highway/traffic. What speed are you going on the highway? I noticed you get about 24mpg at 100, but only like 18 at 130. I need to do more long highway trips to have enough stats, but over a couple of trips to Ottawa that's what it works out to.




Yeah bad smells can be cat-related. Can you describe the smell? The cat itself is as reliable as any other car's cat, but in these cars if the coilpacks go, the amount of unburnt fuel going into the cat increases and the thing dies quickly, even a brand new cat. You said you had those things replaced? Make sure the work was actually done maybe.. who knows.

the work was done by myself in my garage. I double checked everything and made sure that the coils clicked in.

I drive around 110-120 km/h on the highway

As for the smell it is like a burnt rubber kind of smell or like weird plastic i dunno. I heard rotten egg smell is a bad CAT but ive never had rotten eggs for breakfast so im not sure what it smells like. I will cook eggs tomorrow and let them rot for a week or so and compare the smells.

definitely get your cat checked.

My cat is bad (been working on getting it off most of Christmas day, more this morning in a couple hours), my mileage went from 17-22 down to ~9. The only smell that I smell is a burnt plastic/rubber smell, from stuff around the cat heating up and melting.

Most cars the cat starts smelling like rotten eggs, but I've never heard of that smell with a rotary. I think our exhaust gas temp is so hot usually we start frying surrounding materials outside the cat, and the rotten smell is probably burnt out or overwhelmed or something.

When your cat has reached critical failure, as mine has, it will be a serious amount of trouble to maintain highway speed. I can have the pedal to the floor in 3rd gear and it simply can't breath enough to get over 74mph @7500rpm. In 6th, I can't accelerate with anything short of the pedal to the floor, anything less I start losing speed. (Accompanied by the whiff of rubber/plastic smoke, exterior cat temp over 400 degrees, etc...). I have brand new coils, plugs, air filter, cleaned MAF, and reset e-shaft sensor, all which failed to restore my power loss. If it isn't my cat, it is my compression, but WOT under 4k rpm feels perfectly normal, so I don't think it's compression.

If you run into that, get the RPMs low fast, and crawl home or to a dealer or a shop, because you are on the edge of causing engine damage in the strain, backwash of exhaust, etc...

So the cat was changed earlier in the year, but the coilpacks just recently, when you bought the car? If the previous owner drove around with bad coilpacks he could've killed his brand new cat and let you inherit the problem:\

Rotten eggs smell like sulfur... if you've ever smelled a natural gas leak, it's that smell.

definitely get your cat checked.

My cat is bad (been working on getting it off most of Christmas day, more this morning in a couple hours), my mileage went from 17-22 down to ~9. The only smell that I smell is a burnt plastic/rubber smell, from stuff around the cat heating up and melting.

Most cars the cat starts smelling like rotten eggs, but I've never heard of that smell with a rotary. I think our exhaust gas temp is so hot usually we start frying surrounding materials outside the cat, and the rotten smell is probably burnt out or overwhelmed or something.

When your cat has reached critical failure, as mine has, it will be a serious amount of trouble to maintain highway speed. I can have the pedal to the floor in 3rd gear and it simply can't breath enough to get over 74mph @7500rpm. In 6th, I can't accelerate with anything short of the pedal to the floor, anything less I start losing speed. (Accompanied by the whiff of rubber/plastic smoke, exterior cat temp over 400 degrees, etc...). I have brand new coils, plugs, air filter, cleaned MAF, and reset e-shaft sensor, all which failed to restore my power loss. If it isn't my cat, it is my compression, but WOT under 4k rpm feels perfectly normal, so I don't think it's compression.

If you run into that, get the RPMs low fast, and crawl home or to a dealer or a shop, because you are on the edge of causing engine damage in the strain, backwash of exhaust, etc...

holy smokes that is great advice. Exactly what im going through. I will take it to the dealer after the holidays.

and yes the CAT was changed in july 09 and I bought the car in october. I changed everything right away myself.



One last important question: When the dealer changes a bad CAT are they suppose to like reflash the ECU or something? Because the engine goes into protection mode if im not mistaken correct?

holy smokes that is great advice. Exactly what im going through. I will take it to the dealer after the holidays.

and yes the CAT was changed in july 09 and I bought the car in october. I changed everything right away myself.



One last important question: When the dealer changes a bad CAT are they suppose to like reflash the ECU or something? Because the engine goes into protection mode if im not mistaken correct?

You can reset everything yourself without issue. No reflash is needed.

As a follow up though, When I removed the cat and put on the midpipe, I was at 1 tick under half a tank, at 68 miles on the trip. As soon as I finished doing the pipe swap, I left on a 10hr trip, and I filled up the first time at 212 miles on the trip, 13.4 gallons. So I went from ~68 miles on the first half to 144 miles on the second half.

I got serious for a tank, and got 345 miles on the tank, then decided it was too boring so stomped on it as I found opportunity, and my next tank was 290 miles on 14.1 gallons.


(all yesterday and this morning, RI to Ohio, basically all highway)

You can reset everything yourself without issue. No reflash is needed.

As a follow up though, When I removed the cat and put on the midpipe, I was at 1 tick under half a tank, at 68 miles on the trip. As soon as I finished doing the pipe swap, I left on a 10hr trip, and I filled up the first time at 212 miles on the trip, 13.4 gallons. So I went from ~68 miles on the first half to 144 miles on the second half.

I got serious for a tank, and got 345 miles on the tank, then decided it was too boring so stomped on it as I found opportunity, and my next tank was 290 miles on 14.1 gallons.


(all yesterday and this morning, RI to Ohio, basically all highway)

hmm, I just wish I can get 290 miles outa a tank :(

Wow, even my worst mileage, all city and punching it, is always over 320km per tank (~200mi). My best (all highway and babying it without using AC) is closer to 620km per tank (~390mi). '07, 6MT, 12,000mi.

Something is wrong if you're only getting a piece of that.

Here is a pic of my cat that is caused the drop in mileage from 18-22 down to 9.

http://www.rx8club.com/attachment.php?attachmentid=149778&stc=1&d=1262011672

The chunks are the front honeycomb, and there isn't enough material laying there to make up the front one, so I assume the remainder is particulate matter packed into the 2nd honeycomb.

My new '09 R3, just turned 1400 miles and so far the best I've got is about 19mpg, 95% hwy. and granny driving most of the time.
Avg. 17, I hope warmer weather brings a little increase.. 400 a month for gas will get expensive. Last tank went to 247miles. I remember my '04 got right about the same though.
You would think as smart as some people are someone would come up with a way to pull more MPG from these motors.

You will see better mileage as your engine breaks in but don't expect over 22MPG or so.

The big engines that make big power also have enough torque down load to lug the weight around. We don't have torque low, so they have to gear up to increase where we sit in the revs, and this is one thing that drops the max mileage.

The other thing to consider is that you are pulling ~186hp per liter. Pretend you have a small block v8 (what, 4.2L? I don't know my v8s) pulling 186hp per liter. That's 781hp. Any v8 with that much power has far worse gas mileage than we do. A 3.6L V6 with 186hp per liter would be 669hp. Again, worse mileage than we have.


Look at the bright side, it should be worse. Get a beater and break even in 2.5 months from gas savings.

It's the warm up time and winter gas.

Try warming up a V8... then complain about MPG or Kilometers per tank

my v8 actually got far better mpg then my rx8 ever got, and the same quarter mile time and automatic heh. it was a big boat of a car though

i typical get 150 a tank and 220ish pure highway.

My new '09 R3, just turned 1400 miles and so far the best I've got is about 19mpg, 95% hwy. and granny driving most of the time.
Avg. 17, I hope warmer weather brings a little increase.. 400 a month for gas will get expensive. Last tank went to 247miles. I remember my '04 got right about the same though.
You would think as smart as some people are someone would come up with a way to pull more MPG from these motors.
go buy a prius :nopity:

I just filled up 14.1 gallons, 9 days and 285 miles since last fillup. 70% highway, alot of time spent in 4th and 5th gear instead of 6, WOT often, lots of warm-up idel time, etc... I can pussy foot the throttle for 24mpg+, but that's no fun.


I guess I am convinced that this is what the Renesis is capable of, and anyone that doesn't get this mileage has something wrong , or at a bare minimum, isn't running at full healthy.

Stock NA (well, loaned midpipe atm, new cat goes in tomorrow), 93 octane, aggressive throttle usage, Lucas UCL as a light premix, Castrol 10w40, fuel trims and e-shaft sensor reset often... ~24 seconds 0 - 120mph. I can accelerate smoothly without concern in 6th gear from as low as 33mph (32 starts bogging a bit).

I'm not sacrificing anything to get this mileage is what I am trying to say.

Shrug.

How would you know your cat went to crap, would you get a CEL? Is there any other way of knowing its ruined w/o taking it off and checking it

Sorry, no way to tell. There is not a CEL

How would you know your cat went to crap, would you get a CEL? Is there any other way of knowing its ruined w/o taking it off and checking it

There might be, there might not. Cats have several different ways they can fail. Some of those are quite noticable and apparent, some aren't.

If you are out driving, and pull over and look under your car, if you see the cat glowing red, it's definitely toast. Severe cases of this will also have smoke from melting / burning shielding and plastic nearby, this smoke can also appear to come from the engine bay, since smoke rises, and once it rises into the transmission tunnel, the only way to go up is forward into the engine bay, unless you have enough air flow to push it out the back. Your center console rearward of the shifter could also get very hot. Not just the ~85f degree temps that are normally there, but like 150+

If your car feels like it is choking to death, and the harder you push it, the worse it feels, the more power you lose, you might have a cat failure the same as mine that I posted on the previous page, where it was basically becoming a complete blockage of the cat, and the exhaust couldn't escape, and wasn't getting clear of the rotor housing, causing a mess of issues.

I did get misfires from my cat failure. AFTER my brand new coil replacement, plug replacement, air filter replacement, e-shaft sensor reset, and MAF cleaning. I suspect that this was because the oxygen content was so low that it had trouble firing correctly.

You can also remove your cat and take a look inside. There are 2 honeycombs, and you should only be able to see one, relatively close to the header side of the cat. The pic I posted shows the 2nd honeycomb, with the sensor tube just before it. The chunks are from the first honeycomb that fragmented. Rapping on your cat might also allow you to hear rattling of chunks, if this happened.

Cat failure symptoms share alot in common with coil failure, plug failure, and engine failure. Figuring out which one is the challenge, although coil failure can lead to plug failure which can lead to cat failure, which at the extreme, can lead to engine failure. So it's always possibly E) All of the above.

Thanks, this really helped a lot!

Just have someone take a look at it, especially if you are still under the warranty then theirs nothing out of your pocket anyways.

But people are right, its winter bro, and its an 8... they arent easy on gas 18/24mpg is what they post and you probably drive it harder than what htey would. PLus its fuckin cold in canada and its january! u gotta expect a little more fuel consumption when its this cold, your makin the engine work harder.

But as i said, it wouldnt hurt to get it looked at just to be safe.

Good luck

My mpg gone to crap fast I'm on pace to get 160 till light comes on use to get 220.... Changing coils and plugs tomorrow if that doesn't do it. Taking it in to the dealer get my warrantys worth.

My new '09 R3, just turned 1400 miles and so far the best I've got is about 19mpg, 95% hwy. and granny driving most of the time.
Avg. 17, I hope warmer weather brings a little increase.. 400 a month for gas will get expensive. Last tank went to 247miles. I remember my '04 got right about the same though.
You would think as smart as some people are someone would come up with a way to pull more MPG from these motors.

or that some people would take the time to research the car they are going buy

^AMEN.... maybe he should buy a BUGGATI

^nah just get a prius and youll never need to bitch about mpg again

I just filled up 14.1 gallons, 9 days and 285 miles since last fillup.....

ive gotten the same mileage :)+1