C-INRED

My wife and I recently returned from a 5,557 mile road trip from Washington State to Indiana and back. I thought on this trip I would keep better track of my fuel mileage and here are the results (DIC=mpg indicated on DIC; Calc=mpg calculated the old fashioned way):

Fill #1: DIC=28.6, Calc=29.16
Fill #2: DIC=29.6, Calc=30.11
Fill #3: DIC=30.6, Calc=31.46
Fill #4: DIC=29.5, Calc=30.22
Fill #5: DIC=30.5, Calc=31.35
Fill #6: DIC=22.2, Calc=22.78
Fill #7: DIC=21.1, Calc=21.63
Fill #8: DIC=23.7, Calc=24.33
Fill #9: DIC=26.0, Calc=26.87
Fill#10: DIC=25.2, Calc=25.55
Fill#11: DIC=28.5, Calc=28.16
Fill#12: DIC=27.1, Calc=27.46
Fill#13: DIC=28.0, Calc=30.06 (log error?)
Fill#14: DIC=30.7, Calc=31.37

Observations:

It looks like on the average the DIC is calculating about 2.5% or .5 to .75mpg low on my car.

On the longest straight highway driving stretch (2,344 miles) with little weather influence (light winds, no rain, etc) and minimal net altitude change the calculated average mileage was 30.92 mpg.

I was typically driving between 67mph (2-lanes) and 78mph (4-lanes) on this longest highway stretch. This encompassed the first 5 fill-ups. There was little to no noticeable difference between the mileage on 2-lane vs. 4-lane roads and the different speeds.

Strong (20-30 mph) headwinds did cut mileage during a couple of days on the return trip by about 4mpg.

I observed little to no difference in mpg between straight gasoline and 90% gasoline/10% alcohol (although it probably was slightly different). The 90/10 product is very common in the Midwest. Interestingly, the alcohol raises the octane so 'premium' in many Midwest areas is cheaper than 'regular.'

Due to high gas prices I often got questions from strangers about fuel mileage. I think many thought I was exaggerating when I told them I was getting 30+ mpg highway.

Mileage for the total 5,557 mile trip including 11 days of mostly higway driving and 7 days around town was 28.24 mpg.

Oh...and we were loaded most of the time...two passengers (about 350 lbs. total) plus a hatch full of luggage!

I love my Corvette!

Scruff Vette

I just finished two road trips. One 1,000 mile and one 1,600 mile trip. Mostly highway miles but a good portion through mountains in VA and screwed up awful traffic in DC. When conditions permitted I cruised at 80-85 and I never use cruise control. Also I did several days of around town driving. Before both trips my avg mpg was 17-18 combined and I did not re-zero. avg after both trips is now 22.

I checked instant milage several times under steady throttle on flat highways in 6th at 75 mph and got 28-29 mpg consistantly. That seems to be my best mpg sweet spot.

peter pan

That is awesome mileage for an A6 Vette a true hwy economy car

rhedrich

on road trip that are hwy i am avg 28mpg. When I driving mixed Hwy/city I am geting 24 mpg. All city 17 mpg.

matsarge

..75 mph seems to be the sweet spot for my 6-spd as well. I get about 31 mpg at 75 mph, cruise control..flat roads.

TX C6

Looks like there was plenty of fun on this one.....

ben dover

Good mpg, my last trip of 1300+ miles showed 27.6 on the DIC including a fair amount of moutain driving.

Vet

Good report!

On my last 6,666 mile C6 road trip, I also compared the DIC mpg verses my own very careful mpg measurements.

For the entire 6,666 miles, the DIC said I averaged 27.45 mpg. My ridiculously careful measurements indicated I averaged 26.90 mpg. Difference in measurments = 0.55 mpg average.

Thus my measurement was about 2% LOWER than the DIC measurement... exactly the opposite of your experience. Interesting.

I have an `06 Z51, running stock Supercar tires... no mods... car is / was bone stock.

I suppose if the DIC measurements were always WITHIN 2.5% of reality on any C6, that would be just fine. There will always be some degree of error... as is with anything.

Also, when we fill up at the pumps and take our own measurments, we are reading the fuel pump gauges and trusting them. Who knows what degree of error may occur with the fuel pump gauges at any given fuel station... etc.

2.5% error margin on this is ok with me. The C6 gets such great mpg overall, I'm almost not even concerned with the details... the car is incredibly efficient, period.

My car would climb up to near 29 mpg average when on the highway going in a straight line in a conservative manner, and never dropped below 26 mpg when racing up and down mountains in low gear, often wide open throttle, with top off or AC on, or in traffic, etc. Ambient temps were between 85 - 105 degrees almost the whole time. Had passenger and a good deal of luggage in the car too. So I bounced between 29 and 26 during the trip and leveled off at 27.45 mpg when I pulled into my garage after returning.

I suspect if I did not have extra weight in the car and the ambient temps were cooler and I did not run so spirited through the mountains, I would have easily average closer to 28.5 - 29 mpg. Some days I had the top off the whole time, we're talking 800+ mile days at almost 85 mph average speed with the top off the whole time... pretty much why I got a "poor" 27.45 mpg average. The slightly lower 6th gear in the MZ6 Z51 tranny takes a little away too. Excuses, excuses!

loubob57

I just got back from a trip to Mississippi. 590 miles each way. I filled up 3 times and got 28, 31 and 32 mpg. I get better gas milage than my sister does with her 2006 Mustang (city and hwy) even though it is a V-6.

Greenvetter

Could the difference in error be speedometer calibration? Has anyone checked it against a GPS or in car Nav unit?

2009 C6

1. What a great car!

2. I can't believe the DIC mileage is so accurate.

3. Great job documenting and displaying your results.

Vet

Interesting thought, but if the speedo, and thus odo, are a bit out of calibration, it would effect both the DIC reading and manual calculations... because I assume the DIC calculates mpg data based on the speedo / odo info, and when we do our own manual calculations we are also using the DIC odo readings... so whatever error exists with the speedo / odo, I'd think it would effect both measurements to the same degree. But I could be wrong! Experts, chime in.

I had speculated that it was the fuel station gas pump gauges that are the culprit (in terms of error) because this is the only data that WE are reading but the car is not.

Not certain at this moment exactly how the car measures the amount of fuel being used... but all we can do to measure fuel used is to measure how much we pump into the tank, reading the gauge at the station fuel pump... if the car does not agree with the station pump gauges, there'll be a difference.

BuckGW

Thanks for the info!

My 07 Coupe (A6, F55 like yours) gets better gas mileage than any car I've ever owned.

j_digi454

I took a 1450 mile round trip to OH to visit my Son. My DIC showed and average 68.8 mph and a 30.0 mpg. I was cruising at 75 mph whenever possible.
I did not do an actual calculation on this trip but in the past, my actual calculation was about 1.5% lower than the DIC, similar to your results.
I'm thrilled that we have it all, power, looks and economy as well (as far as gas mileage is concerned).

*FAÇADE*

Thanks for the info!

danl72

That is great mileage.

scopeguard

I made a 505 mile, each way, trip a couple of weekends ago. DIC said 27.8 mpg going and 28.6 mpg on the return trip. The return trip was single passenger and less luggage. Made the 505 miles in 7 hrs. actual driving time. That's through the city on both ends. Had I drove like a sane individual I could have hit 30mpg but no fun in that.

CETA 256

Most people that ask me what mileage she gets do not believe me. They are amazing machines.

LTC Z06

Good news.

moolys

Yes they are I tell them let`s go for a ride and I`ll make you a beliver and sure enough they where impressed with the MPG`S like you said awsome car