Tofufu

Hello internet overlords! Don't banish me for a fuel economy thread. I've scoured this forum already.

I recently bought a 2010 R3 with 27,000km (~17,000 miles) on the odo. Really nice car, single owner, nothing wrong with it, completely stock. I've started doing the necessary maintenance on it as soon as I got it. My problem is I seem to get terrible gas mileage with it. I do mostly city driving (Vancouver Canada), which means anywhere between 30kph to 75kph driving, stop and go stuff. So far, in 2 months, I've consistently recorded 18L/100km (13mpg). Car seems very healthy, revs fine and makes good power up top, no cold or hot start issue. Here's the maintenance I've done so far:

-Fresh dino oil (5w20, I know I know)
-Diff fluid change (dealership)
-Tranny fluid change (MT-90)
-New Coilpacks (rev. C), wires, and plugs (all from mazmart)
-Cleaned the MAF
-New engine air filter

The old plugs looked like **** and were probably original. In fact, two of them snapped the little metal connection on top when I pulled the wires off them. Anyway, it's all new stuff now. Since, I feel like engine is smoother at idle. Before it would dip a little bit, but still nothing that worried me.

BEFORE YOU TELL ME IT'S MY DRIVING STYLE:

This is my first RX8, but I've had many (only, in fact) manual cars in the past (Mazdaspeed 6, Audi TT, EP3 Civic,...). I know how to drive stick. Here's my usual starting and going to work procedure:
-Start the car, and let it idle for 15-20sec until revs settle to about 1500 rpm
-start driving, shifting at around 3000rpm to let the engine warm up.
-once engine is warm (full middle position on temp gauge, 1 red bar in cluster), I drive it normally, which is to say I shift around 3.5 to 4k rpm
-There is the occasional 5k rpm pull, but in general I would say I granny it pretty regularly.
-I will, however, WOT redline it once or twice a week, in the hope to keep carbon at bay.
-Oh, and I premix idemitsu (3.9ml/L)

NOW! What do you think? Is my mileage normal? My next guesses are: partially blocked cat, O2 sensor, and bad/dragging brakes. I feel, however, that these are somewhat unlikely given the low mileage of the car.

Help me hive mind.

sonicsdaman

iTrader: (3)

if you haven't yet read the new owners thread about 12 times no really read this!

its your driving style /s

only way to know the cats health is to drop it and check. also try giving the car an Italian tune up. did you have the compression checked before you purchased it?

Tofufu

Hey!

I must've read that thread just about 12 times by now. I have not had a compression test done to it yet, partly because it's still under Mazda warranty (engine) for another year or so, so I figured I wasn't in a rush for it. As for the italian tune-up, I assume you mean go for a spirited drive with lots of redlining gears out? I guess I haven't done that yet (I'm too gentle on this thing I swear). I guess I'll try that next, and possibly try to book a compression test appointment. Not too sure where to go, or which dealership has the tools for it.

sonicsdaman

iTrader: (3)

you would have to call the local mazda dealerships or check around locally for a rotary specialist. the tests need to be performed with a rotary specific tester and you will get a minimum of 8 numbers back or demand for them.

you could always try the snake oil known as seafoam to try and help alleviate so carbon. what grade fuel do you use? 91+?

Tofufu

Yeah I understand the rotary compression tests are different, and that I would be getting 3 numbers per rotor, + rpm normalization.
I only ever use Shell V-power 91. Here in West Coast Canada the best stuff is either this or Chevron 94. From experience I'd say the chevron isn't worth the price difference.

UnknownJinX

Oh hey, another person from BC.

I get about the same gas mileage, honestly. It floats around 13~14 with 90% city driving.

Granted, Victoria is not nearly as hectic as Vancouver, but I do drive more spiritedly. I rev to 9k redline pretty often(how can you not?), and usually upshift at 4~5k RPM.

My car has about 93k(58k miles) km on it now.

Assuming everything is healthy, I recommend a drive on S2S while the weather is still good. It's a fantastic drive, and you can also use the highway drive to gauge your gas mileage. Stay under 100 km/h and you should see the EPA rating of 22 MPG. I did some rough math with all the data I have on Fuelly and I should be able to get 19~20 MPG on that stretch since I was going at 120 km/h the whole way.

Oats

I drive a lot of 40-60mph roads with a stop every mile or two and get around 15-16mpg so 13mpg in real city driving doesn't seem unreasonable.

UnknownJinX

Good for you. I only get Shell 91 or Chevron 94 as well since these are the only 2 fuels around here that are E0.

Chevron 94 is only about ¢2 more per litre than Shell 91, though. It ends up being about 1 dollar difference each tank.

But yeah, no true advantage using Chevron 94. I might get on a dyno one day to find out once and for all.

Loki

iTrader: (1)

How are you recording that mileage? Through a scangauge type device, or kilometers to the light? Doing city driving only will definitely burn more gas but 18L/100 is getting close to my mileage while racing, so just want to make sure everything is apples to apples.

I would review yout fuel trims to eliminate the possibility that thr computer is working with good information. They should be near zero under all conditions.

Depending on amount of city driving my car has always gotten 360 to 420km from full to the light (about 52L fill).

Tofufu

Thanks UnknownJinX, that's kind of what I wanted to hear. Someone else with similar car and similar location! It does seem like Highway mileage is much better, but I haven't really gotten on a long enough stretch to have a 50/50 usage sample. Oh yeah, Sea to Sky is amazing in this car. Don't even need to go much faster than 120-130 kph to have a blast either!

Thanks Oats for your input as well. Good to hear.

I think I'll take the 8 on a little trip up the mountain, give it the beans a little bit, and go from there. Maybe take it in for a compression test, coolant flush, and CAT inspection in the next few weeks.

Tofufu

As for how I calculate my mileage:
Fill it until full, reset trip meter. Drive it for a while (I havent driven it to fuel light yet). Then I fill it back up again, and calculate how much fuel I've put in vs mileage on trip meter. For example last night I put somewhere around 38L and I had done something like 209km, so 38L ÷ 2.09 km = 18.1L / 100km. Then I reset the trip meter again for the next fuel-up.

Tofufu

I checked the fuel trims about a month ago before I changed all the ignition bits. It was all 0 (which I thought a little weird. Expected to see 1.x% or so). I'll give it another look today. I use a generic OBDII with Torque Pro.

UnknownJinX

If you have disconnected your battery for a couple of minutes, the fuel trim will be reset.

Do you do a lot of short trips? That will also hurt the gas mileage as the 8 runs pig rich when cold.

wannawankel

I've been getting 13-14 miles per gallon in city driving over the last 6-8 months. Just recently when driving ~ 850 miles form OH to MA, I average 20.5 mpg in my S2. (after the 1 YO battery died while the car was in storage - so everything reset. All maintenance up to date with 12000 mi on new C coils/plugs, wires).