TopFuelTim

I've been keeping a log on my fuel mileage for the past year, and found some things you might be interested in. The car is driven 54 miles daily, with 18 miles city and 36 highway. Over the entire year, my wife and I experienced an average of 22.5mpg with our mostly stock car. I attached a jpeg copy of the spreadsheet, which should be pretty legible.

We filled the car up as much as possible from the same pump at the same Texaco station near home, and never tried to top the car off.

I tried 87 octane for a little while in early 2007, but it really didn't seem to make much difference in fuel mileage. The piston slap seemed a bit louder with 87 octane. On the good side, it seemed to have a little more low end torque than premium fuel. Overall, the car didn't really seem to like 87 octane, even though it can deal with it if necessary (like when I had brain fade during the fill-up on Dec. 17, 2007). Sticking to premium.

The previous owner added 28# injectors (factory was 26) and I was a little surprised the DIC fluctuated percentage wise from real mileage between 8 to almost 12 percent throughout the year. Although not 100 percent, the low percent fluctuations seemed to happen more often in warmer weather, and the higher percent fluctuations seemed to happen in colder weather.

The car seems to get the best mileage during mild weather, but the biggest factor in mileage variation was my wife (who tends to drive a bit more enthusiastically than me - after all she is a former Sportsman champion at Atlanta Dragway). In her defense, most of her driving is city miles. I like it best in spring and fall, when the dadgum A/C unit doesn't "volunteer" to stay on all the time (it runs all the time from 35 degrees to almost 70 degrees Fahrenheit outside temperature). Also, I don't have to run the headlights as much. Both the A/C unit and the headlights make a noticeable difference in gas mileage.

Gas prices changed a LOT over the past year, ranging from a low of $2.259 per gallon Feb 7, 2007 to a high of 3.439 on May 24, 2007. I paid 3.399 a few weeks ago on January 7, 2008. Oh well, nothing I can do there.

Bottom line is we both LOVE this car and intend to keep enjoying it for a while.

Tim Glover

Quickshift_C5

You put 17.506 gallons of fuel into that car, and close to that on many occasions!?

You running that thing bone-dry or what? How was the fuel pump even working?

TopFuelTim

In the beginning, yes, I did. Was going by the trip meter. Scared heck out of myself when I realized that, and as you notice, that practice pretty much went away as time went on ( and I read posts about what happened when the tank went dry. )

00C Just for Fun

Interesting how the DIC always reads high. I wonder how many of the people who brag about the great gas mileage their C5 vettes have computed it for themselves. Even your real # is good for a v8, but 10% is a big variance. Maybe they programmed the DIC to work like the window sticker mileage, unobtainable.

robvuk

He also noted that the car no longer had the original injectors. This will definitely change the DIC computations.

c5streak

Excellent research! It's a mirror image of what our '04 does as my wifes DD. We always use Shell premium from the same station. I checked the accuracy of the DIC for a long time after we bought the car, and it is very close to actual mileage, usually less than 2%. Almost every fill-up, it says 21.8 to 22.4. Not bad for V8 American muscle!

GCubed

I have an 02Z06 with 47K. I get (recorded) 21 to 22 mpg driving to work (combination city/hwy with a heavy foot). I have gotten 28 MPG on the hwy on a trip, but I was going 85mph.

The DIC recorded MPG is very close, and the trip counter works great. I have no problem driving into the reserve range and using the DIC miles left to determine when to refuel.

FASST LN

The DIC on my 2000 generally reads about 2 mpg more favorable than actual fuel mileage, but I have the stock injectors.

This past weekend heading back from Atlanta, from our hotel to our house in Charlotte, I averaged 34.2 mpg while running between 65 - 75 mph (depending on the speed limit). No AC and it was during the daytime.

That computes to about 32 mpg from a car making 350 hp. I couldn't be happier!

Plasticfan

Good info, Tim. I, too, manually compute MPG at each fill up and get about the same figures you show. Of the 4 cars I own, the C5 is the fuel economy champ. Not bad for 350 HP.

Oldvetter

Your DIC is reading off due to the larger fuel injectors. The DIC uses the computers fuel injector pulses to figure the gas used along with odometer (distance travelled) to compute the mileage.

I also average 22.5 mpg when driving to work.

mrm1149

Pretty amazing cars aren't they......

sydneyACE

This thread has been dead for a while, but... this post caught my eye.

I too have noticed this difference when computing my fuel mileage. I'm not 100% on this but, am pretty sure that the DIC reading doesn't account for time the car sits idling. Like I said, I'm not 100% but you'll notice if you sit with your car idling for a while that the AVG reading doesn't drop. I've also noticed that on fill-ups where my car sat idling more often (like in cold weather when I was warming the car up longer) the DIC reading was further off.

kwanderi

My commute is about 70 miles per day and mostly with the cruise set at 75, which is the speed limit here. DIC shows about 29, but when doing the math I only average 27+. Not bad at all for a Vette considering my 08 Civic get 38 with less than half the HP.

rustyguns

2000 vette 6 sp custom high mileage tune stock motor 33 mpg at 60 mph no a/c comp indicates 36 mpg lol

avg 24 in town. she gets lugged alot you keep the rpms under 1500 and skip shift .... these things squeeze the juice!

on the track 6 mpg

ColeTrain'sC5

it does figure in idle time. If you watch INSTANT ECONOMY it'll show you getting 0.0 mpg if you sit idle. This also computes into you overall average