This may be a pointless thread/post. I tried searching for MPG thread but the site is slow as molasses tonight.

This last fill-up, I calculated my mileage to be about 9.7mpg. This was mostly short highway trips and city driving. Spirited acceleration/driving. This is the lowest I've seen. usually I get around 11-12mpg.

I knew when I got this car the fuel economy was going to be bad, but this is just abysmal. Yes, it's complaining. But yes, I still love the car.

My friend commented that I could trade it in for an escalade and get better mileage. I replied saying that I don't want to drive a land barge around.

Still, I can see why the RX-8 qualified for Cash for Clunkers...

Cheers!

 

How are you doing your MPG calculating, math or best guess? Please give us the history on your car. The service it's had parts replaced, miles. Type of driving it gets(long commutes, short trip), fuel used(reg or prem), ever flooded, mods installed. Just any thing that you can add.

 

Yeah, that mileage indicates there is something wrong with either the compression of your engine, or the health of your ignition, or both. The lowest I have ever gotten was ~13mpg with almost non-stop thrashing on back roads for several hours.


Something is wrong with yours...

 

****... so spark plugs and coils can affect mpg?

 

what about oil change?

 

Oil....probably can. But incredibly minorly. low weight oils are better for mileage, less power is needed to move the oil around the engine, and depending on your type/weight/brand of oil, it could degrade one way or another, including losing viscocity meaning better mileage on old oil, as well as dirty oil, which has it's own problems that could affect it. You are talking less than 1mpg in any direction though. Not worth worrying about for mileage. You still need oil changes, but mileage shouldn't be a concern in regards to oil changes.

Plugs and coils though, certainly. A weak spark generally means an inefficient burn, which is generally power loss, and if nothing else, the driver pushes down on the pedal more for the same apparently power level for cruising, so more gas is used. It can get more complicated than that, but a perfectly healthy ignition generally has the best available mileage. Take the BHR coil upgrade. They don't market it as anything but a preventative measure that stabilizes idle and spark for upper ranges, however nearly every owner is reporting an improvement in mileage and power, not much over a health OEM, but still, noticable. A degrading ignition will produce a drastic effect in the other direction.

Edit:
The other big mileage impact point is through compression. If your seals are degrading, through deforming, cracking, separating, wearing away, etc..., your compression will drop, and you will be able to get less and less power out of the same charge of fuel and air. Basically leaking some of that Air/fuel mixture out of the chamber, though it can get more complicated than that.

 

thanks man....makes sense

 

ok if you are below 12mpg on average something is just plain wrong.
Good luck. Try what they said, replacing coils spark plugs etc. Basically a "tune up".

 

I can routinely get 12mpg if I trash on it. Funny thing is this is my second RX8 and both were like this. So it's not like one is healthier then the other, in fact, I would venture to say that my engine is healthier because of this characteristic.

With that said, to the OP, if you are intentionally riding her hard that MPG is NOT normal.

 

you have an issue..

i got 9.3 mpg ave of pure track time over two days.. this is with a lower compression motor with ~ 60k miles on it. got ~20 mpg on the way home from the event..

beers

 

Agreed, something's wrong with your car. I've had mine over 3 1/2 years - never less than 16 mpg.

 

Make sure the routine maintenence is up to date and clean the MAF sensor and E-shaft sensor. Reset the e-shaft profile by using the "20 Brake Pedal Stomp" technique. All RX-8s benefit from the BHR Ignition System, even brand new RX-8s, and the only reason we do not market it based on RWHP gains is because we have no way of knowing the condition of the engines they are being used on. We have measured gains, for sure, and the reports of improved driveability are quite numerous around here.

Do that routine stuff, first, and let us know how it goes............

 

double check your math

 

If it turns out that your ignition system has been weak for a while you may have a bad/clogged catalytic converter, too.

 

Hmm. Good responses.

I used the miracle of math to calculate mpg. I looked at the trip meter at the end of my tank. Took that number and divided it by how many gallons of fuel I filled up with. That's the correct way, right?

I am doing short trips to and from work. I'd say I almost never drive more than 15 miles a day for the most part. On the weekends, I put more miles on it. Mostly it's city driving. I've routinely been getting 11-12mpg. But this last tank I "thrashed" it more around town. Lots of hard first and second gear accelerating, etc.

The car's engine and drivetrain are bone stock. It hasn't been flooded in the time that I've owned it. I use premium unleaded. The terrain around where I drive is hilly. The main mods are a set of Enkei RPF-1's and TEIN S-Tech springs. It has around 35k miles on it now. I bought it when it had 32k miles and I haven't changed the oil yet, though that is going to be done as soon as I get some time on a weekend here.

The suggestion of cleaning the MAF sensor and the e-shaft(?) makes sense. Oil change as someone has said might not make THAT much of a difference. The BHR ignition upgrade sounds like it could be a possible fix. I don't know how to do any of that, but I'm comfortable following DIY instructions.

Further thoughts?

 

That's bad but the MPG on my car has always been weird through three engines. Everything in my car is new and my last city tank I got 15.0MPG on the dot and today I drove 290 miles on 14.2 Gallons (20MPG). I was thinking the premix was affecting my MPG but then I got 20MPG. Go figure.

But definitely your air filter, MAF, coils, plugs, and wires can ruin your MPG.

 

It turns out your car has six gears, not the three you've been driving it in! Try using those upper gears some time. :-) But no, really, something's wrong.

 

jesus... 290 miles on a tank!?!? I just changed my plugs/coils/wires/air filter/clean MAF sensor and I did 190miles on my full tank. Didnt change nadda. I wasted 400$ for a useless tune up.

What is this e-shaft sensor you guys are talking about? Press the brake pedal 20 times when the car is running and then turn it off? What does this e-shaft sensor do for the car? im just curious

 

That's troublesome...

 

im in your exact situation butters. I had the car for about 2.5k miles. If you ever fix your problem let me know. I mean we should get like minimum 220 miles out of a tank with non agressive driving.

 

my highest tank of gas was 295 miles.

i tend to get 220-230 though.

 

Yeah, I'll see what I can do. But I don't want to spend $500 on an upgrade of the ignition system only to have no appreciable improvement. Hrrrmmm.....

 

^I'm almost on par with that...I'll do almost 250 if I'm taking it easy. I'm averaging 17-18 MPG with easy driving and the occasional romp. That seems pretty acceptable.

 

Yeah my motor has only 6k on it and I put the BHR kit on right after the new motor was installed. I also switched back to a stock WIX air filter and ditched the K&N drop in. I am also OCD about tire pressures and stuff. I only run Shell 93 octane fuel, nothing else. I am also running 245/40-18 tires which supposedly hurts MPG. Keep in mind that when I am on the highway I also use the cruise 90% of the time if there is no traffic. In the city I tend to drive aggressively which is why there is a 5MPG difference.

 

You're right at the scheduled time to replace spark plugs. If you change them now, you're not doing anything extra and that might be your problem.

Check vendors here, sparkplugs.com, or Amazon for plugs. You can get them for about $80 a set, versus two to three times that at a dealer.

I believe there were some Ferraris and Bentleys on that list, too. We're in good company.

Ken