Mileage and Performance Question
 

Hey Guys,

I just moved to San Angelo, TX in October from the east coast where they have 93 octane. Here in TX the highest I can get is 91 or if I'm lucky 92 :/

When I first moved here I noticed a severe loss in power at high speeds. There was no pickup and go if I was at 70mph and wanted to quickly get to 80+

The second thing I noticed was a severe loss in MPG :/ I used to get 18-20 city/hwy, now I am getting 15/16 or so.

I have been using an octane booster about every other fillup. This gives me noticeable better power but still not the same MPG

Finally, I have noticed that my oil consumption is much higher than what it used to be. I used to check it about every other week and have to add at most 1/4 of a quart. I checked it a few weeks ago at the 2 week mark and my dipstick read 1/2! I was like WTF? and quite a bit freaked out I let it get that low. Now I am checking every week and finding that I have to add maybe a little less than 1/4 quart every week. Dipstick reads about 3/4 or a little more full.

Sometimes, I also hear a soft pinging at 7-9K RPM. It's so subtle, only I can hear it. I had a car savvy guy ride with me to try and hear it and he couldn't. It is very intermittent. I don't always drive my car hard, but I know it is good for the car to do it every once in a while.

A little information about my car. It is a 2007. I am the 3rd owner. I bought it at 38K miles. It now has 66K after 2 years in my possession. I replaced the spark plugs and ignition coils at 40K. I change my own oil, only conventional oil, though I have had a Mazda dealer do it a couple of times, so Idk if they used semi-synthetic. I also changed the Manual Transmission oil and Differential oil at 65K.

I hope this is nothing unusual. I love my 8 and as a well-paid bachelor, I take care of it like it was my child.

If you guys can offer any help. I would appreciate it. Thanks!

What was the altitude of where you lived on the east coast. If you were close to sea level I don't know if 1800 ft would account for the loss of power you say you're experiencing. :dunno:

You are definitely due for another spark plug change at this point, and possibly coils as well depending what theory you subscribe to. Have you ever changed your plug wires?

Octane booster doesn't really do anything except lighten your wallet. Even if it did boost octane that doesn't help you if you already run premium, higher octane does not equal more power it just resists detonation better. Using 91 octane is perfectly fine.

The car should fix your fuel trims by itself eventually but you could try to reset them, I *think* the 20 brake pedal stomp reset does that but search and find out for sure.

Thanks for the responses guys.

TankerG the elevation is 1884ft as the elevation where I used to live in MS was 214 so I guess that could be a factor. I didn't think the elevation difference was that much, TX doesn't strike me as a highland lol.

Xexok, I have never replaced the wires on the car. I was hoping that the plugs and coils would last longer than 30K. I was planning on replacing them at 75K. I was also thinking about putting the BHR coils in. I read that once installed, they don't need to be replaced.

I was also thinking about doing a direct injection of seafoam cleanout at about 75K. If have heard it's pretty necessary at that mileage of the vehicle. Anyone have any thoughts about it?

Sure. Yesterday and today, I am actually in the process of testing how effective decarbing is. My thread: https://www.rx8club.com/tech-garage-...r-pics-241867/

Hey RIWWP, thanks for the link to your thread. That's real good stuff. I wanted your opinion on what I should do to keep my 8 running for as long as it can. Basically, I am no mechanic. I consider myself pretty smart and have taught myself to do a lot of routine maintenance on my 8, but again I am no mechanic, neither do I have the tools nor the time to keep my car in a garage for extended time (it being my only vehicle) if I open a can of worms or mess something up.

I do not premix my gas, and actually am a little vague on how to do it. Should I be doing this? If my seals blow, is it ridiculously expensive to reseal?

Thanks!

People replace their plugs around 15-25k miles and a lot of people replace coils at about 30k miles just as preventative maintenance. You could always test the coils and find out if they are still good but they do degrade over time. The bhr kit is a good idea, and yes I believe they do last much longer.

If pretty much anything goes wrong internally with your engine you are looking at a full rebuild if you want it to run and last.

https://www.rx8club.com/tech-garage-...-thread-99636/ Some of the info on the first half or so of this thread gets disproven later on so you may want to start half way in or read the whole thing.

I wrote up the answer to that question too, see the new owner's thread in my sig, post #9 specifically.

Thanks for all the responses. I was reading your intro to having this car and I read about the normal oil consumption being about 1/4 every 1000miles. I probably am about 1/4 every ~600miles. Is this within the range of error? Does that sound like I have popped a seal?

It's high, but within acceptable ranges. I am about that with a reflash that ups my OMP injection rate. You would be more like a quart every 100 miles, or shorter, if you have a failed oil control ring. Visible smoke when driving.