cleoent

Ok here's the deal, my car at 18k miles is getting horribly poor gas mileage, i'm in cali, currently it's about 90 degrees outside and cold for us is 35 degrees in the winter at 6am, usually in the winter we're in the low 50's on cold days.

My question is this, would i benefit from the hot plugs? I know a few of you are running the hot plugs and noticed in increase in gas mileage, are there any of you that didn't notice an increase? Speak up if you would. I have 3 options-

1- Go with the hot plugs for the leading and standard for the trailing
2- Go with a standard replacement of leading and trailing
3- My mechanic suggested using the colder trailing plugs for all 4

What do you guys think?

Here's what i'm really after, i really want the people with the hotter plugs to tell me about their experience with hot plugs... thanks

cleoent

btw before anyone tells the n00b to search, i have and have found some great info but nothing concrete. Thanks :D

RX-8 friend

If the current plugs are fouling, then go for the hotter ones. If not, don't change. The hotter plugs work great in winter here. We use the colder ones in summer.

Usually those who get poor mileage let the car idle a lot. This will kill your mileage. This car uses almost as much gas idling as it does on cruise at 100 km/hr. We've watched this using the CANBUS reader.

Nemesis8

iTrader: (3)

So, the hotter plugs were to offset the old flooding issues, right? Now that the flash level is leaner, we don't need them, right? I went stock plugs, hot plugs, stock plugs. I'm getting 20-22 MPG combined MPG on Chevron 92. I could not tell the difference. It's kind of like the stock market, buy/sell who can tell.

Old Rotor

Dont change your plugs unless they are bad. Even if it did improve your mpg, the $100+ would be hard to makeup in mpg increase. Press your right foot slower and you can get 2+ mpg but it is not as much fun.

cleoent

Hmmm, my car pretty much lives in stop and go traffic, looks like this may be the root of the problem.

Great info in this thread, thank you so much!

Xyntax

Don't change them if your car doesn't have any problems. I did not request mine to be replaced, but the dealership changed them anyways due to flooding and per TSB instruction. Ever since then, throttle response, acceleration, gas mileage, and even power has increased dramatically. Most readers here would dismiss my claim, but that's up to them. I'm the one getting improvements :D

btw cleoent, I drive 95% city.

cleoent

I'm confused, you're saying dont change them if you dont have problems... but you got yours changed when you didn't have problems and everything improved...

Xyntax

Oh sorry, mine flooded without my knowledge. I guess I was running lead plugs on one rotor or something. And then I had misfire CEL from time to time. So dealership took out my plugs and found out one fouled. They instead replaced both per TSB.

cleoent

did they replace them with the "hot" plugs?

Xyntax

Yes, that's how I got the hot plugs. I didn't even think anything of it until I got them in my car. That's when I started looking up what changes it would put on my engine now that it's there. Now I'm hooked :D I don't know what would happen if you run hot plugs on all four.

Nubo

I'd only get hot plugs if I was consistently and repeatedly fouling the normal heat-range plugs. That's usually only going to happen if
a) there's some other mechanical or tuning problem (example - "K" flash)

b) consistently and extremely sedate driving (low-speed, low rpm shifts, very short trips) -- aka "granny driving".

Hot plugs are not without problems and can increase tendency to ping or detonate and can increase octane requirements. The idea is to use the coldest plug that will not get fouled in normal use. For most of us that would be the "normal" rx-8 plug, I'd think.

cleoent

i always use 91, so i'm not worried about octane requirements... mostly interested in gas mileage and performance...

rxeightr

Why is that? To dump fuel to protect the cat?

6speed8

Yes, in case anyone has not noticed, IDLING is a major gas waster in the RX-8. That's one of the main reasons why fuel economy suffers on the RX-8 so much, its due to the idling at stop lights.

To those of you getting really bad fuel milage (below 17 mpg), I'll bet you either let your cars idle alot, or you are stopped at red lights or stuck in major traffic.

My RX-8 gets more MPG on 89 octane than on 91. My car gets really terrible mileage on 93 octane and the higher the ootane the more soot on the exhaust tips. Running 89 octane I have noticed the tips stay really clean and the car runs great.

I do not let my car idle any longer than it has to.

RoyalPain

I get 13 MPG at best Last time I drove on the Hwy I was down to 10MPG I don't warm up the engine before I leave for work. I just drive easy until it is at normal operating temp. If I drive aggressively I get better gas milage then I do if I drive conservativley. When I drive conservativley I get about 12mpg I have never seen my car get more than 190 miles per tank. And that is from Fill to fumes.

I have a disadvantage I live in the hills and I work in the hills on the other side of the valley. So I am going up hill to and from work.

cleoent

that freaking sucks, i would not tolerate that, write to mazda, write to bush, write to whoever it takes, that's is awful.

RoyalPain

It does suck but the car is so damn fun to drive I tolerate it.

anbjornk

I'm currently running 98 octane... Should I get the hot plugs? i'm currently getting approx 17MPG mixed driving.

Aseras

just go buy a set of FD plugs for $20.. for all 4 of them.

tell the local auto parts store you have a 93 rx7. get 7's for the leading and 9's for the trailing and put them in and see what happens. then, try using 9's all around and see what happens.

the new rx8 plugs are basicaly a ripoff, just use the cheap rx7 plugs and change them as often as you like, they are cheap and they are instock.

icyur2

Not sure how valid this is, but this is what I picked up from reading other threads..if you haven't done so already, with your high mileage (18k?) try:

1 - Revving it up to 9K often to clear the carbon deposits in the chamber
2 - Reset your car's CPU, by tapping on the brakes 20 times within 1 min. or something like that

Other than that, change your oil often (I use castrol 5w20 dino), and maybe you might get an improvement..wouldn't hurt to try and you'll have fun in the process