PhineasFellOff

INTRODUCTION

Well, as promised, here are my data on 20 tanks during my long distance drive from Los Angeles to Atlanta to Jacksonville, FL, to Houston to Austin and back. Sorry for the delay, but I've had a lot of things to take care of since I've gotten back home. I don't know if anyone else has done a trip of this size, but if not, I believe this may be important FIRST-TIME information for all RX8 owners and would-be owners.

Every tank is with DSC off and TCS off (some people have surmised that mpg may be better with both off). Unfortunately, I did not test with DSC and TCS on, so those comparisons can not be made. Every tank was on the highest octane offered at that gas station in that region of the country. CRUISE CONTROL WAS USED continuously unless otherwise noted (e.g., in city driving in Atlanta or Austin or wherever). A/C was off unless otherwise noted. At the start of the trip, my odometer was at about 12,000 miles. My car had run one full tank with the "L" flash before the trip began. I had not made a comparable trip without "L" flash, so those comparisons can not be made, unfortunately. Every tank included 1 to 3 quick pit-stops either for bathroom (I apologize for my passenger) or rest area (sleep for me). 60, 65, 70, and 75 mph were tested. Please have your atlases ready, guys!

*** Edit ***

My car is a 6-speed manual and was built in September, 2003.

*** End Edit ***



FIRST LEG: LOS ANGELES, CA, TO ATLANTA, GA (interstate 10 to interstate 20, which becomes the 20/59 from Meridian, MS, to Birmingham, AL)

** Note: the date is when I filled up the tank and the mileage is what followed on THAT tank. **

1. Sun 3/21: 368.2 mi/13.878 gal = 26.531 MPG @ 65 mph
91 octane, Shell, Los Angeles to Phoenix, AZ, mostly 82-102 degrees Fahrenheit, 70 degrees at the end
very slightly uphill, I believe

2. Sun 3/21: 323.5 mi/14.567 gal = 22.208 MPG @ 75 mph
91 octane, Union 76, Phoenix to Deming, NM, mostly 50-60 degrees
very slightly uphill, I believe

3. Mon 3/22: 320.4 mi/13.867 gal = 23.105 MPG @ 70 mph
91 octane, Chevron, Deming to Pecos, TX, 55-65 degrees
very slightly uphill, I believe

4. Mon 3/22: 305.3 mi/13.185 gal = 23.155 MPG @ 70 mph
91 octane, Chevron, Pecos to Eastland, TX, 65-70 degrees
very slightly uphill, I believe

5. Mon 3/22: 334.6 mi/14.421 gal = 23.202 MPG @ 70 mph
93 octane, Chevron, Eastland to Shreveport, LA, 45-55 degrees
very slightly uphill, I believe

6. Tue 3/23: 312.2 mi/13.855 gal = 22.533 MPG @ 70 mph
93 octane, Texaco, Shreveport to Meridian, MS, 35-45-55 degrees
got off hwy at Jackson, MS, to look for food/bathroom and did some hard accelerations

7. Tue 3/23: 337.3 mi/13.542 gal = 24.908 MPG @ 65 mph
93 octane, Shell, Meridian to Atlanta, GA, 65 degrees
quite a bit uphill, at Meridian the interstate 20 becomes the 20/59, which goes northeast up to Birmingham, last 37 miles were city driving

Comments: none at this time



FIRST LEG: ON THE ROAD WITHIN ATLANTA

8. Tue 3/23: 286.1 mi/14.725 gal = 19.430 MPG @ various speeds
93 octane, Chevron, Atlanta, GA, 70-75 degrees
city driving and fwy driving, no cruise control, LOTS of hard accelerating

Comments: saw a titanium and a silver RX8, waved to both, and got waved back by both; the most beautiful city in America; couldn't help pushing my car to the limits in Atlanta, which is unsurprising if you have ever experienced Atlanta roads, which are incredibly narrow and winding and are perfectly suited for the RX8



SECOND LEG: ATLANTA TO JACKSONVILLE, FL (interstate 75 to the highway 23)

9. Thur 3/25: 56.1 mi/2.022 gal = 27.745 MPG @ 60 mph
93 octane, Shell, Atlanta to McDonough, GA, 75 degrees
slightly downhill on the interstate 75, no stops, got caught in bumper-to-bumper traffic in the last 10 miles and got off hwy in McDonough, GA, to refill tank and gauge mpg gotten because I knew it would be my highest ever

10. Thur 3/25: 330.9 mi/13.501 gal = 24.510 MPG @ 60 mph
93 octane, McDonough to Jacksonville, FL, 55-65 degrees
the hwy 23 is a winding country road and oftentimes going slightly uphill, had to break out of cruise control often and slow and speed up again

Comments: The leg from Atlanta to Jacksonville is around 350 miles, which is short enough such that differences in mph mean very little difference in arrival time, which gave me the perfect opportunity to test 60 mph and try to get maximum mpg. However, I met with two unfortunate circumstances. First, unbelievably, I got in a traffic jam on the interstate 75 going south out of Atlanta (tank 9). I don't know how much mileage was drained from 10 miles of traffic jam but at least I chose to get off the hwy at McDonough, GA, to refill and calculate my highest mileage to date: 27.745 mpg. Second, instead of taking interstate 75 down to interstate 10, I made the extremely unfortunate decision to take hwy 23 at Macon, GA, which looked like a much more direct route from the atlas but wound up zapping my mileage (tank 10). But this tank from McDonough to Macon, according to my car's gas gauge, would have topped the 27.745 mpg. And it would have been a significant difference, too. What a shame. I should have taken the 75 all the way down.



SECOND LEG: ON THE ROAD WITHIN JACKSONVILLE

11. Fri 3/26: 50.8 mi/2.529 gal = 20.087 MPG @ various speeds
93 octane, Shell, Jacksonville, FL, 60-70 degrees
city driving, no cruise control

Comments: nothing to do except watch Dawn of the Dead; 28 Days was better



THIRD LEG: JACKSONVILLE TO HOUSTON, TX (interstate 10)

12. Fri 3/26: 349.3 mi/13.729 gal = 25.442 MPG @ 60 mph
93 octane, Shell, Jacksonville to Pensacola, FL, 55 degrees
slightly uphill

13. Sat 3/27: 321.7 mi/12.384 gal = 25.977 MPG @ 65 mph
93 octane, Shell, Pensacola to Baton Rouge, LA, 70-80 degrees
slightly uphill, last 25 miles were city driving in Baton Rouge

14. Sat 3/27: 300.2 mi/13.565 gal = 22.130 MPG @ 75 mph
93 octane, Shell, Baton Rouge to Houston, TX, 75-85 degrees
last 20 miles were city driving in Houston

Comments: Again, my efforts to get maximum mileage @ 60 mph are thwarted by a less-than-ideal fwy that gradually inclines (tank 12).



FOURTH LEG: HOUSTON TO AUSTIN, TX (hwy 290)

15. Mon 3/29: 168.8 mi/7.284 gal = 23.174 MPG @ 75 mph
93 octane, Shell, Houston to Austin, TX, 65-75 degrees

Comments: beautiful, straight country road with farms



FOURTH LEG: ON THE ROAD WITHIN AUSTIN

16, Mon 3.29: 157.5 mi/8.764 gal = 17.971 MPG @ various speeds
93 octane, Chevron, Austin, TX, 75-85 degrees
city driving, no cruise control, lots of accelerating

Comments: an unusually high percentage of Mazda cars of all kinds on the road. Can anyone explalin this? Aranda's has the best REAL Mexican food I have EVER had at super low prices.



FIFTH LEG: AUSTIN TO LOS ANGELES (hwy 290 to interstate 10)

17. Tue 3/30: 278.3 mi/12.132 gal = 22.939 MPG @ 70 mph
93 octane, Chevron, Austin to Sheffield, TX, 45-55 degrees
quite a bit of gradual uphill, put in 1 quart of Castrol 5W20 before leaving Austin

18. Wed 3/31: 309.4 mi/13.677 gal = 22.622 MPG @ 75 mph
92 octane, Phillips 66, Sheffield to El Paso, TX, 55-65 degrees

19. Wed 3/31: 347.2 mi/14.253 gal = 24.360 MPG @ 75 mph
91 octane, Shell, El Paso to Tucson, AZ, 70-75 degrees
gradual downhill, A/C on all the way, traffic accident caused bumper-to-bumper condition just outside Tucson

20. Wed 3/31: 366.7 mi/14.409 gal = 25.449 MPG @ 70 mph
91 octane, Tucson to Cathedral City, CA
gradual downhill, A/C on for the first 60 miles

Comments: I had gotten used to gauging reference points on my car's gas gauge but it seemed the tank (tank 17) coming out of Austin threw everything off. The only change I can think of is that I added a quart of oil just before leaving Austin. Surprisingly, A/C appears to have little or no effect on mileage (tanks 19, 20). Any comments on these two issues?



CONCLUSIONS

1. 75 mph: hwy cruise: 22.1 to 24.4 MPG (avg 22.9; 5 samples: tanks 2, 14, 15, 18, 19)

2. 70 mph: hwy cruise: 22.9 to 25.4 MPG (avg 23.4; 6 samples: tanks 3, 4, 5, 6, 17, 20)

3. 65 mph: hwy cruise: 24.9 to 26.5 MPG (avg 25.8; 3 samples: tanks 1, 7, 13)

4. 60 mph: hwy cruise: 24.5 to 27.7 MPG (avg 25.2; 3 samples: tanks 9, 10, 12; however, all three tanks were from highly compromised portions of the trip)

5. The lowest realistic speed for hwy driving is 65 mph, although most people drive 70 to 75 mph. Driving 70 mph instead of 65 appears to cost 2 mpg, whereas driving 75 mph instead of 70 costs 1 mpg. People who prefer to drive under 70 mph should feel good about the gains in MPG. People who prefer to drive around 70 mph should feel good that they lose only about 1 MPG when pushing it up to 75 mph.

6. It is clear to me that, if not for the compromised conditions in my 3 samples at 60 mph (tanks 9, 10, 12), my car would have gotten significantly above 27.7 MPG. This may lend support to others in the forum who have claimed 29 to 31 MPG.

7. Air conditioning (A/C) appears to have little or no effect on MPG (tanks 19, 20).

8. Adding oil may affect the rate at which the gas gauge falls, which makes no sense to me (tank 17).

*** Edit ***

9. It should be noted that, before this trip, in Los Angeles commuting mostly on the fwy, I had been averaging right around 21 MPG, with a handful of lows in the 18's and several high 22's and one in the low 23's. Hence, the mileages from this TRUE long-distance trip on CRUISE CONTROL is HIGHLY IDEALIZED and are different from fwy driving in one's city area.

*** End Edit ***


Please comment on any issues (such as #7 and #8 above) and add your own long distance mileages on cruise control. We NEED more data from owners, which can only benefit us all.

Nubo

What is the effect?

PhineasFellOff

My gas gauge went down faster, such that I thought I was getting lower-than-expected mileage such that I panicked and refueled early only to find out that the actual mileage was comparable to what I got earlier on the trip at that speed.

Spin9k

Great stuff... thank you... so now finally(!!!)...... you've given us all a benchmark that can't be denied, refuted, dissed, or argued PhineasFellOff.

Our gas caps are off to you! :D :D :D

Any comments on butt fatique or general comfort?

willhave8

Wow - it has been demonstrated pretty clearly in earlier threads the most significant variable to MPG was time on the highway. I have also witnessed that. This pretty much confirms that.

However, in my own half tanks on the highway experience (pretty consistently at 65 to 75 for 125 miles) I have never gotten over 20MPG. I only have 2000 miles on my car. Does the low mileage on my car speak to my lower MPG or is it something else?

My 8 is a summer 03 production with whatever flash that was.

PhineasFellOff

You're very welcome.

The comfort was fantastic, in my opinion. My passenger reclined the seat all the way down to sleep for much of the trip. She commented positively that it felt just like a plane. There are the overhead reading lights and the seat reclines comfortably just like in an airplane.

Elara

You, sir, kick *** . Maybe now everyone will believe those of us who have gotten similar mileage before, but didn't document it as well as you have.

Trx8

Nice Results, Thanks.

PhineasFellOff

I don't know what is the key factor for your car.

My car was getting mid to high 22's occasionally in local Los Angeles mostly-fwy driving even before "L" flash (even when it was around 2000 miles on the odometer), with a handful of lows in the 18's for abundant-city driving. There's nothing special about my car since I got 18.0, 19.4, and 20.1 MPG while doing extensive within-city driving during my trip.

shebam

Great report, thanks. In your cruise control driving, were you in traffic that changed speeds often, or were you able to "set and forget?" I put on about 650 miles last weekend, but on NJ Turnpike, etc., had to keep varying speeds within a range of 65 - 80, even though average may have been 70 or less. Result was 20 - 22 mpg. Also it seems that if the car is "used" to commuting it takes a few hundred miles to get best highway results, re both performance and mpg. Any support for such a hypothesis?

PhineasFellOff

My tanks were all done on cruise control "set and forget" unless otherwise noted (e..g., going from Atlanta to Jacksonville, hwy 23 required me to slow and speed up quite often, which along with the winding, gradually-uphill grade, hurt the MPG).

I'm not sure what you mean by "used to commuting." When you say commuting, are you talking about driving around your city with combined hwy and city driving so that the ECU may have to adjust itself from the start of a TRUE long distance drive on cruise control?

I'm not sure about the answer, but if you refer to the data at the very beginning of my trip, you'll notice that I got 26.5 MPG (my second-highest on the trip) at 65 mph coming out of Los Angeles in the hot desert at 102 degrees Fahrenheit. This has led me to believe that the ECU doesn't need much adjustment time at all. Rather, I believe the rotary and/or ECU needs ABSOLUTE CONSISTENT STABILITY to produce high mileage. However, I'm not sure, since I have no technical expertise at all.

pp13bnos

Very well done! 25+mpg would be great, but I'll be happy with my 20-21mpg. CJ

BTW, Pineapple Racing was talking about making a taller 6th gear for people who would like to be able to cruise at 75mph@3k rpms. There was a thread I started about this somewhere....perhaps it will generate more interest now that we have some awesome data?

beachdog

PhineasFellOff, very commendable. Don't know how you were so disciplined for such a long trip. Thanks for the service.

Next trip can you throw in a couple of segments at 80 and 85?

downshift

That's right! 80 to 85 would be a more realistic number.

RXMAN16

Good Job. Thanks for the info

tblazer

80-85 mph -- hmm. Who's going to pick up the tab for the man's speeding ticket if he gets one? Haha.

I owned a '79 RX-7 (don't have an 8 . . . yet). I recall the best mileage I ever got was a 5-6 hour trip at night with little traffic where I could keep the speed very steady. So perhaps as was noted, stability is a key factor here.

Also, I'm curious if anybody has any observations regarding optimal ambient temperature, if there is any.

And finally, since there seems to be a somewhat wide range of experiences here on mileage I'm thinking driving style could obviously be a factor. But also, is it possible that the engine tolerances are off a smidgen for those with poor mileage? OK, I'm out of my league technically here, but I'm wondering if a really tight fit between the rotor housing and the apex seals could be a bit taxing in terms of efficiency. Or, maybe it's too loose a fit and compression is lost. In any case, has anyone noticed any correlation between oil consumption and mpg? That is, are those who are getting very good mileage burning any more or less oil than those who are getting poor mileage? The oil burning could perhaps speak to tight or loose tolerances of the engine, and the tolerances could perhaps alter fuel economy. I know when the apex seals on my RX-7 went, I burned a ton of oil and I seem to remember mpg went down. Somebody check me here if this is completely off base. Otherwise, any thoughts on this theory?

Nordic RX-8

Good report! I have less than 1500 miles on my RX8, and have been refered to by my co-worker as "a granny driver" - I have yet to see MPG over 20. I took a trip last week from Indy to Chicago and back (~380 miles) with 5% city/95% highway at 70 mph using the cruise control and averaged 19.6. My co worker has a WRX STi and drives like he stole it - he says his mpg is ~21.

shebam

Unfortunately, I mean creeping most of the way for 9 miles in to work in stop-and-go traffic on some days. I was thinking maybe it's not so much how long it takes for the ECU to adjust as the plugs or cat getting gunky, particularly if you say "I ain't going anywhere anyway so might as well keep the revs low." This is similarly uninformed speculation.

PhineasFellOff

I'm not doing this trip in my RX8 anymore. In a year or so, I'm going to buy a Honda Accord Hybrid (which is coming out in fall 2004). At that point, I will reduce the accumulation of miles on my RX8 by driving the Accord as often as possible, including on all distance trips. Well, maybe I might take the RX8 on a shorter trip to, say, Las Vegas.

I will NEVER test 80 and 85 mph, NO WAY!!!!

therm8

Nice info.

Very similar numbers to what I've noticed. Made a 1200 mile round trip recently. Keeping my speed at 80 mph (all interstate), I averaged just over 23 mpg for all 1200 miles. About half was hilly terrain (drove from Jax, FL back home to WV).

My normal commute is about 40 miles, mostly highway. That combined with my normal around town driving usually averages about 19.5 mpg (ends up being around 70/30 highway/city). This is with 9500 miles and original PCM flash.

PhineasFellOff

Hey, this is the info that beachdog and downshift and probably others wanted to know. What happens at speeds higher than 75 mph?

Apparently, there is a phenomenon of diminishing "losses." In other words, as you increase in speed from 65 to 70 to 75 to 80, you continue to lose MPG but you do so at a decreasing rate.

downshift

Thanks for chipping in, therm8! That's some insightful information. Good job, you two!

therm8

Bear in mind that I have the AT, so at 80mph my revs are at 3300 rpm. For the MT it is higher I think?

TybeeRX-8

what about wind effect. West to east matches the prevailing wind flow in the US, except for storms. Also, no mention of inclement weather, if any, and any supposition as to any possible effect + or -. I've seen 21+ once, but may local driving style puts me at 16+. As noted, however, in another thread, in my first full tank after the "L" flash, I got 18.2 in the same type driving.:p

ptiemann

you are going to keep both cars? or was there sarcasm in your posting?