Hi everyone

I've had my RX8 for about 6 days now and I love it....however....I've already filled it up twice, and it's due for another fill up today.

I'm getting maaaybe 14-15mpg. I've been at cruise control on the hwy, set at 68. I've done very little driving around town. I have a killer commute (70 mi each way), so I expect to spend a lot of money on gas. Yea, this wasn't the most practical car

My point isn't that I'm spending a stupid amount on gas—that was a given. My issues is simply the mileage itself. I figured I'd be averaging 20.

Is there anything in particular that could be influencing gas mileage that much? What should I do?

My future husband has a Prius, but this isn't balancing out as much as I was hoping it would

Thanks for your input!

 

that doesn't sound normal. in city driving, especially when you have a heavy foot, that kind of mileage is common; on all highway driving, if you're not speeding and keep it in top gear, you should average relatively high. i've averaged the advertised 24 on highways. maybe taking it in for a check up? year/mileage of the car?

 

How are you computing your gas mileage? Many of the poor fuel economy threads are incorrectly based on the 15.9 fuel capacity and filling up when the low fuel light comes on.

https://www.rx8club.com/rx-8-discussion-3/how-improve-mpg-comprehensive-195544/ does have some useful info.

 

how many gallons have you put in since you bought the car? how many miles have you driven since you bought the car?

 

Wait wut ? you drive an 8 and he drives a Prius ?

and yes 14-15 is low for that type of driving . Check you are working it out right as mentioned above and if so take it in for a service .

 

definitely not normal.

for cruising on highway at 68 with 6th gear, you should be expecting 20-25mpg

 

yes, that mileage is possible with all city and super start/stop driving, not highway. get it checked out.

and honestly, there ppl that mis-compute the mpg's by using the tank size instead of the actual usage like expo and brettus said

 

I do 50/50 and cruise in the mid-upper 60's everyday. I get around 19mpgs. 14-15 is not normal (unless you're full throttle in every gear and cruising in 5th). And 15% of the highway driving is bumper-to-bumper traffic

 

question 1: how are you calculating your mpg?
question 2: what gear are you in when cruising on the hwy?

I do a lot of highway driving and despite my heavy foot, I get at least 17 mpg.

 

Given that you did your math right why don't you tell us your vehicle's maintenance history?

 

seeing as he has owned the car for only 6 days (well, 7 now), i doubt he knows a whole lot about the maintenance history. common things to check would be coils and plugs if you are truly getting that mileage on the highway. i have heard people mention how their highway mileage improved after new coils and plugs.

i get 15-16 mpg average but i do mostly city driving and it is usually only 10 miles at a time since i live close to downtown. if i am driving only on the highway, i can easily get 22-23 mpg without really trying.

it sounds like it would be worth getting checked out and to verify all applicable recalls have been performed.

 

are you using 93 octane cuz if your not millage will suffer and you might be damaging your engine. i say this because a buddy of mine used 83 and his millage dropped to nothing and he had alot of knock in the engine.

 

if i remember correctly, 91 is the recommended octane but around here, most stations only have 87, 89 and 93. premium is definitely what you should be using though whether it is 91 or 93.

 

i dont think i've ever seen 91 octane to be honest

 

Although I rarely check my gas mileage (I can't handle the truth!), I religiously zeroize my trip odometer(s) each fillup. It's a simple matter of how many miles you went on how many gallons it took to re-fillup. Just as simple as calories expended vs. calories intake.

 

Sunoco around me has 87, 89, 91 and 93. I still use 93...

Oh and BTW...I daily drive rougly 75 miles highway (with 5-7 miles of residential mixed in) at 75-80 average and get 22-23MPG consistently. I can almost scrape 300 miles from a tank.

 

You're in Connecticut, you can go ahead and use 5w20 oil if you're not already, it helps with the gas mileage.

 

I have a 2008 rx8 AE edition with 6 speed manual. car has 2,900 miles on it, I use premium fuel, 5-20w oil, etc.

I am lucky to get 16 mpg on the highway. I clock every fill-up and note the miles/gallons thinking my calculations are off, however it is the same every time. I generally cruise between 80-85 on the highway, however I did not see a huge improvement when I tried, painfully, to drive at 70...

that being said, I find it amusing that between my three cars, my jeep is the fuel efficient one, at least when compared to the two 8's (13mpg and 16mpg). I am getting 20 mpg all day long on the highway at 80 with that bad boy.

 

I only do city driving and I get 15 on avg *I have a heavy foot...* So yeah, something is not right with yours if you are doing the math correctly. If you are, it could be a few things like Coils/Plugs/Wires. Best to find out as soon as possible.

 

at 80-85 in sixth, all fuel injectors are pushing fuel in and two extra intake ports are open. Under 3750rpm only the primary injector is firing, which has a finer fuel atomization and helps with better gas mileage. So it's sensible to say that as you increase above 3750rpm your gas mileage will begin to suffer more and more.

 

Drove for 6 hours at 80 MPH in 6th, and I was getting 20-22 MPG. Definitely not 15...

 

exactly ^

 

I'm at 4k rpm in 6th (overdrive) at 80 mph. The two 'extra' ignition ports open at/above 5k rpm (at least according to my 'butt dyno'). Overdrive is supposed to facilitate more fuel efficient highway driving.

However I rarely go 80 or below in my early morn commutes.

Of course for optimal fuel efficiency you should never break 3k rpm nor 50 mph. But then why have an RX-8???

 

your butt dyno is wrong.

 

check: tire pressure, plugs and ignition coils, air filter.