So, when I first got my 2004 BB MT with 57k miles my gas mileage wasn't terrible. Probably around 14-18 MPG, which is somewhat average. But over the three months I've owned this thing it's gotten gradually worse and worse. Last night when I filled up I calculated 11 MPG. I don't drive the car very hard that often, not enough to get that low of MPG. So I know there's a few things that could be causing this. The first thing I was gonna do is buy new Spark Plugs considering I have no idea when the previous owner got new ones. Anyone else have any suggestions?

Note: This is my second RX8, so I know the gas mileage to expect, don't treat me like a n00b

 

Do the usual maintenance and check-ups:
Ignition (spark plugs, wires, coils, whatever)
Catalyzer

How long does 1kg of added oil last?

Recent modifications?

Maf\IAT conditions?

 

in no particular order :

plugs you already got
coils
leads
clean the maf
new air filter
check for vac. leaks
have the front o2 sensor checked for accuracy

 

zach: listen to Brettus and Bse, odds are your problem lies in there somewhere.

Is the car stock? (aside from visual mods) OEM intake?
routine maintenance is critical for our cars.
if you have a multimeter you could check the coils.

 

Zach, my MPG is usually 18-22, but when my cat fried up, it dropped my MPG to ~9. If the coils, plugs, wires, MAF sensor cleaning, new air filter, and e-shaft sensor reset don't fix it, get the car in to a dealer to look at the cat.

 

I'm installing a supercat next week, so we'll see what that does. I have a K&N drop in filter, but my oil light has been occasionally coming on, so i'm going to add some oil now.

 

mine was at 9 mph ... motor flush / oil change .. .now im at 18 mpg .... i really hate water vapor / that milky crap

 

motor flush?

 

replace your coils, wires and plugs. i did mine yesterday and my mileage has shot right up,113 km and not even a quater tank used. idles very smoothly and pulls alot harder.i wish i had done this when i bought her a year and half ago and really for a few hundred bucks you cant go wrong.

 

oh forgot to add disconnect the negative as well to reset your full trims too.not bad for an hour and a halfs work.

 

I get about 15 Mpg; at 85 to 90 Mph....
Running too rich.
/seriously

 

I get 13mpg, at best. This is my second RX8 and both have been this bad. Not complaining. I swear.

 

Your oil light came on and you didn't immediately add oil?!?!

 

For comparison. 2004 with 104,000+ (third engine )

 

How many miles were on the car when you got it and how many now?

 

Mines a joke too.
Oh well.. It's worth it.

 

motor flush is poured into the oil and ran for 10 min .. then when you drain the oil ... a lot more crap comes out.. it has cleaners in it ... most importantly it lowers the viscosity of the oil so it all comes out very quickly

 

The problem with that is there are still three quarts in you oil coolers with that Flush running for thousands of miles before your next oil change. I would change it sooner.

 

I get close to 20 during highway driving 70-80mph.

But If I do city driving for the whole tank, its really sad - like 11.

My car hates city driving. I've seen fuel needle move just while warming up sometimes.

 

there is no way you put in 18 gallons into your car!

 

poor Zachy

 

Is it a AT or MT?

 

mt

i'm sayin coils too

 

A Clean MAF does wonders plus the ECU rest.

Don't forget we are still using winter gas which reduces MPG.

 

i always get a solid 19mpg under normal driving.