04 rx8 6spd gt, Clean k&n filter, 68kmiles 25k on motor, everythin else is stock. No shutter or hard start problems evrything seems fine except for the mpg. I've owned the car since 2008 and alwas averaged 18/19 combined city/highway. Pulled plugs and they seem to hve rusty deposits on the electrodes. Ill upload pics from my pc asap not sure if you can on mobile version. Ballin on a budget at the moment so not wanting to throw unecessary parts at it.

Thanks. Hopefully not beating a dead horse with another mpg thread.

 

beat the dead horse back to death...

When was the last time the car was serviced?

 

From my thread: https://www.rx8club.com/new-member-forum-197/new-potential-owners-start-here-202454/

Gas Mileage:
If you are considering, or have purchased, an 8, you will likely have one of 3 opinions on gas mileage:
1) I am buying a sports car, or won't be driving this regularly, so I really don't care about mileage
2) I care a bit about mileage, but I think what I get is fairly reasonable
3) WTF, I am getting terrible mileage, these car's suck! All RX-8's are gas guzzlers.

If you have the first or second opinion, then congratulations and join the club. If you have the 3rd, then keep it to yourself, we aren't interested in listening to it. Gas mileage has been discussed, killed, resurrected, killed again, reincarnated, burned alive at the stake, beheaded, cremated, and BURIED AT SEA. Please leave it there.

The reality is, a healthy RX-8 will get 17-18mpg city, 22+mpg highway. But 'healthy' means completely healthy: healthy coils, wires, plugs, O2 sensors, carbon free engine, good compression, healthy cat (or no cat), good transmission/diff fluid. Let even one of these slide, and your mileage WILL drop, and it will drop fast. If you believe that RX-8s simply can not get this mileage because you have never seen it, then there is only 1 person to blame, and that is YOU. If you don't get this mileage, then there is something wrong with one of the above points. Or with your foot. Your right foot can make the mileage drop quite a bit as well. And I don't mean granny driving as the answer to good gas mileage. Smoothness is more important than speed. Smooth and fast is better mileage than unstable and slow.

People also tend to point at it being a 1.3L engine, and assume that a 240/238/232 hp rotary "2-stroke" engine is as efficient as a 1.3L 4-stroke piston engine (which is probably in the 70-90hp range). This simply is NOT the case.

So if you can't get this mileage, start poking around for what is wrong.

For reference, here is 8,330 miles of mileage data from my Sevenstock trip around the country in September 2010. The lowest tank was 13.99mpg (14mpg basically), and that was in non-stop tight curves on the Pacific Coast Highway where I was having fun blasting along. Note the 4 tanks over 23mpg, 11 tanks over 20.00mpg. Also note how the highway mileage drops as speeds go up. Once you cross the ~70mph range, the wind resistance does start stacking against you more and more. It's easily a several MPG drop going from a cruise of 70 to a cruise of 80+. And those were probably closer to 85-90. The 18mpg in northern NV wasn't really highway, but it was alot of really straight empty terrain, and speeds that I won't talk about publicly







So, short story? 13mpg means something is wrong with your car if you aren't driving it around at full throttle everywhere.

 

Awesome pic!! You must have been iching to use it. Thanks for the info. I drive the **** out o her and love every minute of it and have always had 17 mpg minimum so gonna start with plugs and go from there. Last mechanic service was for a neutral safety switch a year ago that's all. Didn't believe the autozone scanner that told me my manual trans had. Neutral switch, who knew. Done my own service since 42k brakes, trans/diff fluid at 55k and reg oil changes of course. Anyone have any details on the 100k powertrain waranty and what it covers just out of curiosity.

 

100k factory warranty is JUST the engine itself. Nothing else. Not even stuff that has to get replaced when the engine does, stuff like fluids, fuel line, etc... They re-used as many components as possible and bill you for the rest.

There is a whole thread dedicated to it.

 

picture of deposits on spark plugs. never seen this kind of build up before. any hints?

 

When you say that you are getting 13mpg, is that one calculation, or have you run through multiple tanks of fuel? When did the drop in mpg begin?

As for your plugs... They don't really look unusual for 25k+ miles, but they are more than ready to be replaced. Any idea how many miles are on them? (Hint: It's not a given that that new ones were installed with the motor replacement.)

 

A couple of thoughts:

Look at the plug tip from the side, is there a lot of erosion on the electrode that comes out from the side? From the top, it does not look too bad. If there is not really any erosion on the bottom, it is probably not too bad. It does look a little like it is having a bit of trouble firing thought.

I did not see coils mentioned. Are they the original ones? If so, I would do those first They are a few bucks more than the plugs, but IMO needed first. A good coil will fire a bad plug, but a weak coil will not fire a good plug. Mazmart has set of the Mazda ones for about $200, that is where I got mine. Some of the autoparts stores, like O'Reillys, have an aftermarket one for less ($30 ish), but I have not seen or used them. The coils work 2 to 3 times as hard on this motor as any other. I am waiting for folks to post experiences with the cheap ones before I try them.

A few questions: do you hear a faint chirping sound when you start the car? Just one quick chirp? People have associated that sound with coils. Also, pull them off. There are a lot of posts on the white dots on the back of the coils indicating they are bad. If you see pitting on the metal plate behind the coil, it is really a bad coil. I had pits behind 2 of my coils on my 04 when I changed them at about 68,000.

Lowest budget approach, 4 cheap coils and clean the plugs. Then ECU reset (will likely happen for you when you disconnect the battery before changing the coils), get a few drive cycles in and re-evaluate. Plugs might be needed too, that is a lot of miles. While you are dirty, look at the suggestions in the $100 thread in my signature, specifically the engine grounds. You can do a cheap grounding mod with a dozen stainless steel star washers from Lowes and a little connector grease between each ground lug and the body (tighten enough to get the star washer tips through the paint to metal). The ground path on this version is not the best.

Good luck, Then do the rest of the stuff in the $100 thread : )

Mike