DrDiaboloco

Damn, I barely broke 25. I guess I need to slow down to 65-68 to get those extra few mpg.

Kewl

This is the first trip I've taken since getting the scan guage and it showed some interesting data points. First, there was no magical rpm or speed where the mpg took a sudden nose dive. Even as the rpm passed thru 4k (steady state driving, not accelerating) the mpg only continued it's slow drop. Drop to 23.xx mpg at 80mph. This proved to be the case even at higher rpm in lower gears, e.g. 80mph in fifth gear. Second, to a point, a slower speed did not always translate into higher mpg. I didn't have a chance to really study the lower speed mpg, other than to say that 6th gear use at speeds of 40+ gave the best overall city mileage. Third...intake temp did not seem to impact mpg. At an IA temp of 70 the mpg was the same as an IA temp of 100+ at the same speed/rpm.

The most interesting behavior noted was, with all things being the same, road, speed, rpm and A/C operation, mpg would drop considerably once it started to rain hard. I encountered this behavior several times while drive on the interstate. Where I would see a dry 23+mpg once I enter a rainy area mpg would drop to 18 or so. Once out of the rain it would return to 23+.

DrDiaboloco

I noted this behavior on another thread, from a long road trip I did a couple of months ago... Mileage that I'd expect from other hwy tanks on the same day, 24-25mpg, dropped 10-20% in hard rain.

Kewl

One would think that with the cooler, denser air that rain provides you would see engine performance actually improve, and given nothing else changed the mpg would improve also. Did (does) anyone have any idea why we are seeing lower mpg instead?

r0tor

iTrader: (1)

-shrug-

moete87

iTrader: (1)

I get 210 a tank. Thats if im lucky!

glassetcher

I totally agree. This "miles per tank" is a worthless measurement. IMHO, only an average over AT LEAST three tanks would be acceptable. And that is a bare minimum. There are SO many variables that can factor into this calculation! For those claiming 300+ miles on a tank, what is the worst you have recorded? And, how many tanks were at the 300+miles vs. the ones that were 200 mi/tank?

After 1 yr+ of recording every tank of gas, I would say I have averaged about 18.5mpg. Range is from 17.2 to 22.2mpg.

I guess I would put those who claim a 350 mi tank in the same category as those on the other end that complain about 12MPG mileage. If either one is true, there is definitely something wrong with their ride!!!

DrDiaboloco

I'll guess it's because of the added drag of driving through the water on the road surface.

A couple of months ago, I was tearing along in a driving rainstorm at highway speed, and when I went under an overpass where there wasn't any standing water, the car suddenly accelerated (a little) with a constant throttle opening. A second later, when I hit the standing water on the other end of the overpass, I felt the car decelerate. It wasn't anything super-dramatic, but it did lend credence to my theory.

DrDiaboloco

Well, if you're doing that well on average, you must have a lot of highway or reasonably steady-state medium-speed running in there. In the stop-and-go grind (traffic, traffic lights, stop signs, etc.) I can't come close to averaging 20mpg. I mean, c'mon, not even ONE tank below 15mpg? It looks like you haven't even had one below 17 for that matter, whereas probably half of mine are 17 or below when I don't have any highway or steady-state running in there (and I don't pound on the car by any stretch, except intermittently). It's the acceleration away from all the stop signs and such that seems to kill the mileage.

Kewl

I have found that the mileage just sitting (still) at idle is terrible. Okay for die hards...the gas consumed while sitting at idle is high. Much higher than an average piston engine. I agree mileage while waiting for a light - for example - with the engine at idle is zero. So while stop and go hurts mileage for sure the rotary at idle uses lots of gas...

Point? Don't spend any more time at zero speed with the engine at idle then you absolutely must.

r0tor

iTrader: (1)

my daily commute is about 1/3 city, 1/3 highway, and 1/3 mountain roads

Brettus

iTrader: (2)

read somewhere that the 8 uses at much gas at idle as it does at 65 MPH !

MadDashRX8

And what about fueling at different stations, using a different pump at the normal station, turned facing the opposite way at the normal pump, variations in levelness, etc., etc., etc... Just a thought.

Nubo

What about it? Try it and see for yourself.

Kewl

Different station/different pump, and facing the other way can certainly impact the amount of fuel you can get in the tank and hence your mpg figures. On my recent trip I was running a scan guage II on the car the whole trip and it provided realtime figures that supported the 27+ mpg I got. Shown here with the engine off...

DemonRX-8

I too have noticed that the car gets much worse mpg when you spend any significant time idling. I used to get about 15 mpg in the early days when I used to let the car warm up until the temp gage gets moving (yes, I fell into that trap!). Stopped that and my mileage went up to around 17 mpg on average around town driving.

I recently started adding pre-mix (8 oz per tank) on a trip to FLA a few weeks ago and noticed a considerable increase in mpg. I consistantly got 290-310 MPT on 14.3-14.5 gallon fillups (87 octane always) for an average of about 21.5 mpg for the trip - my car had at best barely broken 20 mpg with all highway driving before that trip (probably 80 mph avg). Now I'm not a 55-65 mph kind of guy so I'm not expecting 24-27 mpg, and this trip was with AC running 100% of the time and speeds averaging 80-100 mph. i.e. this trip was run faster and harder than previous highway runs. One stint I was following my brother in his Cayenne where we averaged about 100 for an hour or so . . . hit a max speed of 115 for the trip on that leg!

Not trying to get this tread sidetracked, but the pre-mix definitely made a difference . . . $0.50 of pre-mix per tank is definitely worth a couple mpg (which basically equals a couple free gallons of gas per tank - you do the math!). I didn't post right away because I wanted to run it a little bit longer to see how it does around town.

And before anyone complains MPT doesn't mean squat, yada, yada, yada - I do save receipts and have logged just about every tank of gas I've ever put into the car (range, gallons filled, octane, gas station, etc . . . 32500 miles now) and have tracked mpg per tank, three tanks, and six tanks.

KuzuRyuuSen

that is very true. i used to get 16 mpg for 100% highway, but i just got 23 mpg yesterday for the first time ever with my 8 for 95% highway driving. now i have an incentive to drive slowly.

BunnyGirl

My best so far has been 25.61 with mixed driving, which includes downtown traffic, stopping at every block to every other block, and wonderful I-84 traffic at early rush hour where you spend about 20 minutes sitting and/or moving at about 10-15 mph. By the tiem you finish this you have gone maybe 2 miles. Then you hit I-5, and if you are lucky you get to move. This sucks because I only need I-5 for maybe 500 feet before I exit and my lane is for exit only at the very next exit after getting on I-5. I haven't had a chance to do a long highway trip anywhere. I drove up to Seattle in April but I'd already used up about 75 miles before I started out, doing mostly city/suburbs driving. Then after getting to Seattle had to deal with their lovely rush hour and city driving (stopping at every block for long periods of time) as well as idling for about 35 minutes trying to leave a parking garage. I got 23.21 out of that tank. I'd like to take a long highway drive on a full tank to see what I can get.

My second best mileage was 24.18, which I just got this past week.

Edit: My average is 23, which means high 22s to mid 23s consistently. My worst tank was my first that was 19.47, I beleive (19 something). That is when I kept repeatedly stalling it, letting it warm up excessively long, et cetera.

GiN

My personal best so far has been 275 miles on 13.3 gallons. That was last winter when the sun and moon and stars happened to be aligned correctly for this to happen. On a regular daily commute I drive 55 miles highway and 7 miles street. That 55 miles is 50% (Los Angeles) stop n go. I only get gas when the warning light comes on. 13.3 gallons is the average volume I fill to get the pump to click off automatically. 245 to 255 per tank has been normal for my car. 210 was the worst, which was my first tank from the dealership.

Razz1

I still prefer to use 3rd grade math and calculate the miles per gallon not per tankful.

dsmdriver

iTrader: (3)

The pre-mix comment is interesting to me.

I used pre-mix at the track a few weeks ago. I also got the latest flash and broke 10,000 miles within a few days of all of that, so I have no idea what is really going on, but I'm getting much better MPG now. I assumed it was the 10,000 mile breakin thing, but I wonder if the pre-mix is still helping? I'm only two tanks of gas in from the pre-mix, and I filled at half tank both times, so some of it is still in there.

Humm. I'll have to test this over the next few months...

samsong

One relevant factor in the MPT dialogue is if you use ethanol or not...I think ethanol is not as dense as "normal" gas. I wonder if the 87 vs 93 octane difference is somehow related to the additives and the gas density. RotaryGod?

dsmdriver

iTrader: (3)

E85 ethahnol has about 15% less energy in it than normal gas. A 15% mix of ethanol in gasoline will reduce the MPG by a few percent, but not the 50% variation we are seeing.

The difference if you get 200 miles per tank is only 5 miles.

stask1

Same is here: 04 6spd RX-8, low gas comes on when I do about 220-230 miles.
Averaging about 18,XX MPG with mostly highway miles.
On the weekends when I drive in the city it uses about 12-15 mpg!
That is sucks!!!

DrDiaboloco

Don't know what to tell ya. I've had very few tanks that were "mostly highway" or all-highway that returned any MPG value that didn't begin with a "2". It's just a matter of how far past 20 it was (22-25 is typical). My "city" mileage is very similar to yours, though, if you jack up your range by about 2mpg on the low and high end.

As for the incredibly accurate "low fuel" light, the best I've yet done is a smidge over 300mi before it came on. In my personal experience, the light comes on about 20-25mi or so before the needle actually bottoms out on "E". Then I go to the next gas station and fill up with 13.6-14gals, so in MY car, the light means "you've got about three gallons left" and the needle at the "E"-peg means "you've got about two gallons left".