I think the DIC is less accurate in city driving than on the highway.
[Z06] Average MPG DIC not accurate?
Thread Starter
Safety Car
Joined: Mar 2006
Posts: 3,538
Likes: 9
From: Pasadena, CA
Average MPG DIC not accurate?
I just filled up with 15.5 gallons. My trip read 288.6 miles. Calculating those numbers would make ~18.6 MPG. The DIC read 20.8 MPG. I think that's a significant difference...
Racer
Joined: Feb 2007
Posts: 251
Likes: 0
From: Springdale AR
I've noticed the same thing, though mine is about 1mpg off. If it says 23.8 avg, it really works out to about 22.8 or sometimes a bit less. So I'd say mine is 1 to 1 1/2 mpg off. I wonder why that is. I wonder where the DIC gets the average calculation from. I would assume it's averaging from the instant mpg number.
Le Mans Master
Joined: Dec 2001
Posts: 7,788
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From: Winchester TN
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St. Jude Donor '03-'04-'05-'06-'07-'11
Hi DitchTehFish -
The computer does not recalculate for each tankfull - it is a running average.
best regards -
mqqn
The computer does not recalculate for each tankfull - it is a running average.
best regards -
mqqn
Racer
Joined: Feb 2007
Posts: 251
Likes: 0
From: Springdale AR
It will recalculate if you hit the reset button for average mpg. you can do this at any time, but I usually do it after each tankful. And I'm not sure if it counts idle time either.
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Michael S. Palmer
Safety Car
Joined: Dec 2000
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From: Town of the cow
Funny how the DIC always errs on the high side. BTW, this is true for all cars I have owned. If it erred on the low side they would be getting cars in for warranty repair to fix the low mileage issues.
Joel
Joel
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Joined: Dec 2001
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From: Winchester TN
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St. Jude Donor '03-'04-'05-'06-'07-'11
I see - I never reset that - never have the whole almost 50k miles on my Z.......
I do have an excel spreadsheet that I keep that shows every tankful and the average mpg.
I will update it tonight and see how it stacks up to the DIC.
I just wish they had come up with a different name for the On-board Computer - I would rather be talking about my OC than my DIC.
best regards -
mqqn
Melting Slicks
Joined: Oct 2001
Posts: 2,786
Likes: 22
From: Cary NC
The miles to empty works much the same way.
So fill up, reset ave mpg. After you get to about half tank then the ave mpg and miles to empty will settle down and be reasonably close. I've run mine down on fumes once and questioned the amount of miles to empty it told me. Either that or there is a spare gallon hiding in there somewhere
Melting Slicks
Joined: Oct 2004
Posts: 2,730
Likes: 92
From: Lakeland FL
Overstates mileage in city driving....
I have put 12k miles on my stock 03 Z06, overall average is 21.7 actual mpg at 40 mph. Indicated display typically overstates mpg 0-3 mpg particularly in mixed and city driving.
Interpolation of speed versus actual mileage indicates 19.4 mpg at 30 mph, 21.6 at 40 mph, 23.7 at 50 mph, and 25.9 at 60. Best tank ever was 27.4 mpg at 67 mph, worse was 15.6 mpg (19.1 display) at 30 mph.
Another interesting point-range is sometimes optimistic, acts and calculates like car has bigger fuel tank than it does.
The great gas mileage is just another bonus for driving a Z.
Interpolation of speed versus actual mileage indicates 19.4 mpg at 30 mph, 21.6 at 40 mph, 23.7 at 50 mph, and 25.9 at 60. Best tank ever was 27.4 mpg at 67 mph, worse was 15.6 mpg (19.1 display) at 30 mph.
Another interesting point-range is sometimes optimistic, acts and calculates like car has bigger fuel tank than it does.
The great gas mileage is just another bonus for driving a Z.
Le Mans Master
Joined: Mar 2002
Posts: 5,955
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From: PNW
I've keep fuel records on my Zee for awhile. Below is the deviation of the DIC MPG vs the calculated (trip miles/gallons to fill up). As you can see, it fluctuates a bit, and I'm sure it's due to driving style. A negative number means the DIC MPG was less than the calculated, so it's not always higher - there were a few instances.
Some of the higher deviations were during winter storage when the car would get started and ran a lot without actually moving out of the garage. When driving on a regular basic, the DIC MPG is usually within 2% ~3% of actual MPG.
A 3% deviation at 20 MPG is 0.6 MPG. I'd say that's not too bad.
0.83%
1.86%
2.81%
1.98%
3.08%
2.05%
2.72%
2.91%
2.86%
6.25%
8.27%
2.65%
3.80%
0.96%
1.52%
1.78%
1.88%
2.66%
0.16%
2.58%
-5.00%
1.82%
6.10%
-1.49%
5.69%
2.64%
2.64%
4.53%
1.74%
4.41%
1.98%
5.74%
4.12%
2.91%
4.15%
3.29%
1.76%
3.15%
5.70%
3.37%
Some of the higher deviations were during winter storage when the car would get started and ran a lot without actually moving out of the garage. When driving on a regular basic, the DIC MPG is usually within 2% ~3% of actual MPG.
A 3% deviation at 20 MPG is 0.6 MPG. I'd say that's not too bad.
0.83%
1.86%
2.81%
1.98%
3.08%
2.05%
2.72%
2.91%
2.86%
6.25%
8.27%
2.65%
3.80%
0.96%
1.52%
1.78%
1.88%
2.66%
0.16%
2.58%
-5.00%
1.82%
6.10%
-1.49%
5.69%
2.64%
2.64%
4.53%
1.74%
4.41%
1.98%
5.74%
4.12%
2.91%
4.15%
3.29%
1.76%
3.15%
5.70%
3.37%
Last edited by ZeeOSix; Jun 27, 2007 at 02:12 AM.
Tech Contributor
Joined: Oct 1999
Posts: 41,063
Likes: 9,827
From: Charlotte, NC (formerly Endicott, NY)
The other problem is the way people average their fuel mileage. Using 15.5 gallons for 288 miles may not get you the number of miles per gallon as you have no way to verify the tank is full even if you fill it to the point gas is flowing out of the filler or a way to know for sure that they tank was down to the same level it was at the last time you filled it up. Fuel tanks on cars made since the early 70s are extremely difficult to fill to the top as they have an expansion area to keep fuel vapors from escaping from the car. This causes variation in tank filling due to vapor pressure, how level the ground is when you fill the car, etc. You are always going to have an error of a gallon or two at each fillup. One time you are going to put more in and the next time less depending on these variables. The only way around this is to average the mileage over 10 fillups which will help reduce the impact of the errors as an error of too little gas on one fillup will be compensated by adding more gas on the next. Another way but probably not feasible is to run the car out of gas and put in a known amount and then run the car until it is out of gas again.
Bill
Bill
Thread Starter
Safety Car
Joined: Mar 2006
Posts: 3,538
Likes: 9
From: Pasadena, CA
The other problem is the way people average their fuel mileage. Using 15.5 gallons for 288 miles may not get you the number of miles per gallon as you have no way to verify the tank is full even if you fill it to the point gas is flowing out of the filler or a way to know for sure that they tank was down to the same level it was at the last time you filled it up. Fuel tanks on cars made since the early 70s are extremely difficult to fill to the top as they have an expansion area to keep fuel vapors from escaping from the car. This causes variation in tank filling due to vapor pressure, how level the ground is when you fill the car, etc. You are always going to have an error of a gallon or two at each fillup. One time you are going to put more in and the next time less depending on these variables. The only way around this is to average the mileage over 10 fillups which will help reduce the impact of the errors as an error of too little gas on one fillup will be compensated by adding more gas on the next. Another way but probably not feasible is to run the car out of gas and put in a known amount and then run the car until it is out of gas again.
Bill
Bill
Instructor
Joined: Jul 2007
Posts: 136
Likes: 0
From: pasadena california
my current car a Mercedes e320 v6 gets 25 mpg babying the crap out of it on the hwy and in the city i get around 13-14mpg and ill tell you this it doesn't have anywhere close to 405hp its a dog.
so please stop complaining you guys get way more mpg than any other sports car that compares to the z06.
btw i got to drive a gts viper last month for a good 4 hours and i went threw 15 gallons in nothing but city driving now thats bad gas mileage.
so please stop complaining you guys get way more mpg than any other sports car that compares to the z06.
btw i got to drive a gts viper last month for a good 4 hours and i went threw 15 gallons in nothing but city driving now thats bad gas mileage.
Pro
Joined: Jul 2004
Posts: 625
Likes: 0
From: Anaheim Hills CA
if you're worried about gas mileage, you shouldn't be buying a 405HP sports car 
honestly I have no idea how much gas mileage I get....I never checked it nor do I car
p.s.- I should be free saturday to remove your BSM's
honestly I have no idea how much gas mileage I get....I never checked it nor do I car
p.s.- I should be free saturday to remove your BSM's
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
BTW, the methodology used by the EPA has been changed for 2008, resulting in slightly poorer mileage rating compared to the current system. The vehicle's fuel economy won't change, but the EPA rating will.