Calculating gas mileage...
Thread Starter
Racer
Joined: Aug 2014
Posts: 400
Likes: 28
From: St. Paul (smokey!) MN
Calculating gas mileage...
I've seen several threads mentioning gas mileage. I did a road trip from Lafayette, IN to Cincinnati, OH (and back). Filled up in Lafayette with 91 no-ethanol, made the trip, and filled up when I got back.
The instantaneous mileage reading in the DIC bounced around 27-30 mpg for most of the trip, cruising at about 75 for most of the way.
Calculating my mileage by trip odometer reading/refill when I got back puts it at 26.7 mpg.
Another question - over what range/period is the Average mileage calculated? I doubt it has ever been reset. Before the trip, it was saying about 22. Afterwards it said about 24. I should have tried resetting it before starting the trip, but didn't think to do that.
It appears the computer is overestimating the mileage. Is this normal? Not that I actually care - I don't expect it to be an economy car. I still think almost 27 is doing good.
'98 Vert, top up for the trip, M6.
The instantaneous mileage reading in the DIC bounced around 27-30 mpg for most of the trip, cruising at about 75 for most of the way.
Calculating my mileage by trip odometer reading/refill when I got back puts it at 26.7 mpg.
Another question - over what range/period is the Average mileage calculated? I doubt it has ever been reset. Before the trip, it was saying about 22. Afterwards it said about 24. I should have tried resetting it before starting the trip, but didn't think to do that.
It appears the computer is overestimating the mileage. Is this normal? Not that I actually care - I don't expect it to be an economy car. I still think almost 27 is doing good.
'98 Vert, top up for the trip, M6.
Melting Slicks
Joined: Sep 2011
Posts: 2,258
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From: Appleton WI
If you reset the average MPG, it will calculate based on miles driven from that point. I don't know what the miles would be if you never reset it. I'm sure it gets to a certain mileage and then drops off the oldest info or resets completely. Given that you increased your average MPG by 2MPG on your trip, I suspect it isn't from the beginning of time.
The average MPG does seem to be optimistic when compared to hand calculation. Nothing new there.
The average MPG does seem to be optimistic when compared to hand calculation. Nothing new there.
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To get an accurate reading on mpg for a trip, yes, you need to reset the display to zero. Otherwise, your Mpg is being based on a lot more mileage than you are actually traveling.
Melting Slicks
Joined: Sep 2011
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From: The beautiful Alabama Gulf Coast!!
According to the owners manual, Average is the fuel economy calculated for the current tank of fuel, or since you last reset the display. Even if you never reset the display, you're only seeing the average for the last 18 gallons or so.
Team Owner
Joined: Mar 2001
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From: small town in S.E Pa. PA
St. Jude Donor '03-'04
This car is 20 years old, the algorithms are binary.. the module does not know when you fill the car.. the longer it calculates the MPG the more accurate the output. ( example.. ) if you set the reading to Xerox while at the top of a 2 mile long bridge, took the car up to 50 mph and at the top reset the reading to zero and coasted the mile on the down side.. a reading of 50 or 60 MPG would be entered into the logic algorithm. it would calculate one mile and see a miles per gallon of 50 or 60..
Also sitting at a light or idling for a long period of time, would enter 0 miles into the logic and also enter ( eg. ) a gallon burned. thus making the 1 gallon usage vs. miles achieved inaccurate. Ideally. if you were on a level highway with slight increases and decreases for fuel demand and very close accurate reading could be achieved.. Also an average trip no mater what the conditions the binary algorithm will be fairly accurate. but the longer the sample was active, the more accurate it would be.. We are talking relative average driving conditions.. IN any event advertising 20+ mpg on a high performance sports car was considered economical when other common passenger cars were not getting that level of economy..
Also sitting at a light or idling for a long period of time, would enter 0 miles into the logic and also enter ( eg. ) a gallon burned. thus making the 1 gallon usage vs. miles achieved inaccurate. Ideally. if you were on a level highway with slight increases and decreases for fuel demand and very close accurate reading could be achieved.. Also an average trip no mater what the conditions the binary algorithm will be fairly accurate. but the longer the sample was active, the more accurate it would be.. We are talking relative average driving conditions.. IN any event advertising 20+ mpg on a high performance sports car was considered economical when other common passenger cars were not getting that level of economy..
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This car is 20 years old, the algorithms are binary.. the module does not know when you fill the car.. the longer it calculates the MPG the more accurate the output. ( example.. ) if you set the reading to Xerox while at the top of a 2 mile long bridge, took the car up to 50 mph and at the top reset the reading to zero and coasted the mile on the down side.. a reading of 50 or 60 MPG would be entered into the logic algorithm. it would calculate one mile and see a miles per gallon of 50 or 60..
Also sitting at a light or idling for a long period of time, would enter 0 miles into the logic and also enter ( eg. ) a gallon burned. thus making the 1 gallon usage vs. miles achieved inaccurate. Ideally. if you were on a level highway with slight increases and decreases for fuel demand and very close accurate reading could be achieved.. Also an average trip no mater what the conditions the binary algorithm will be fairly accurate. but the longer the sample was active, the more accurate it would be.. We are talking relative average driving conditions.. IN any event advertising 20+ mpg on a high performance sports car was considered economical when other common passenger cars were not getting that level of economy..
Also sitting at a light or idling for a long period of time, would enter 0 miles into the logic and also enter ( eg. ) a gallon burned. thus making the 1 gallon usage vs. miles achieved inaccurate. Ideally. if you were on a level highway with slight increases and decreases for fuel demand and very close accurate reading could be achieved.. Also an average trip no mater what the conditions the binary algorithm will be fairly accurate. but the longer the sample was active, the more accurate it would be.. We are talking relative average driving conditions.. IN any event advertising 20+ mpg on a high performance sports car was considered economical when other common passenger cars were not getting that level of economy..
Team Owner
Joined: Mar 2001
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From: small town in S.E Pa. PA
St. Jude Donor '03-'04
I try very hard not to sound like an engineer... Trying to use simple analogies and non technical jargon will only help people understand.. Its not about how much I know, or trying to show what I know. its more about transferring the knowledge to others so they understand it. One of my greatest pleasures was teaching engineering to 4th and fifth year engineering co-op students. When the light actually went off in their heads understanding an engineering principle, I could see the joy in their faces.. Very rewarding.. I've come here to try to give some insight into this car. as humbly as possible.. some embrace that, and others seems to feel intimidate by it in the form of disrespect.. the reason for so many train wrecks driven by my own hand. IM not the mean and miserable person some make me out to be.. Ill help anyone if I can, I don't clam to know it all as some suggest.. I also do not take any disrespect from anyone.
Bill aka ET
Bill aka ET
Le Mans Master
Joined: Sep 2014
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From: Kelowna BC
In the past, with other cars; I fill to first click, start counting miles until the next fill up to first click. Gallons to fill and miles logged = pretty accurate MPG. Also done it with 2 fills.
For the most part I really don't care TBH (unless I thought something was wrong). It is what it is, I need gas when I need gas regardless. The DIC tells me 15.9 (Z06, city driving only, fairly heavy foot, around 10 miles each way to work and back). Sounds about right to me.
For the most part I really don't care TBH (unless I thought something was wrong). It is what it is, I need gas when I need gas regardless. The DIC tells me 15.9 (Z06, city driving only, fairly heavy foot, around 10 miles each way to work and back). Sounds about right to me.
Last edited by grantv; Aug 4, 2017 at 02:05 AM.
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Thread Starter
Racer
Joined: Aug 2014
Posts: 400
Likes: 28
From: St. Paul (smokey!) MN
This car is 20 years old, the algorithms are binary.. the module does not know when you fill the car.. the longer it calculates the MPG the more accurate the output. ( example.. ) if you set the reading to Xerox while at the top of a 2 mile long bridge, took the car up to 50 mph and at the top reset the reading to zero and coasted the mile on the down side.. a reading of 50 or 60 MPG would be entered into the logic algorithm. it would calculate one mile and see a miles per gallon of 50 or 60..
Also sitting at a light or idling for a long period of time, would enter 0 miles into the logic and also enter ( eg. ) a gallon burned. thus making the 1 gallon usage vs. miles achieved inaccurate. Ideally. if you were on a level highway with slight increases and decreases for fuel demand and very close accurate reading could be achieved.. Also an average trip no mater what the conditions the binary algorithm will be fairly accurate. but the longer the sample was active, the more accurate it would be.. We are talking relative average driving conditions.. IN any event advertising 20+ mpg on a high performance sports car was considered economical when other common passenger cars were not getting that level of economy..
Also sitting at a light or idling for a long period of time, would enter 0 miles into the logic and also enter ( eg. ) a gallon burned. thus making the 1 gallon usage vs. miles achieved inaccurate. Ideally. if you were on a level highway with slight increases and decreases for fuel demand and very close accurate reading could be achieved.. Also an average trip no mater what the conditions the binary algorithm will be fairly accurate. but the longer the sample was active, the more accurate it would be.. We are talking relative average driving conditions.. IN any event advertising 20+ mpg on a high performance sports car was considered economical when other common passenger cars were not getting that level of economy..
The next time I do a road trip I'll reset it and compare the computer average with the trip odometer/gas pump method. I had read here that the computer over estimates mileage, I was trying to confirm that.
Team Owner
Joined: May 2001
Posts: 25,058
Likes: 1,265
From: Virginia
St. Jude Donor '11
Not complaining, just curious about how the computer did the calculation. Going from 22 to 24 over a 350 mile trip tells me it the period is more than the last fill up but less than the last reset, which was long ago. It does not automatically reset on a fill up.
The next time I do a road trip I'll reset it and compare the computer average with the trip odometer/gas pump method. I had read here that the computer over estimates mileage, I was trying to confirm that.
The next time I do a road trip I'll reset it and compare the computer average with the trip odometer/gas pump method. I had read here that the computer over estimates mileage, I was trying to confirm that.
heres a thought...start with a full tank...write down the mileage...drive it until half full...go fill er up...subtract the mileage you wrote down from the present mileage at present fill up...divide the number of miles driven by the number of gallons it took to fill er up with....5th grade math...you do not need to be an engineer to figure that one out...right?
Last edited by Yello95; Aug 4, 2017 at 12:25 PM.
Thread Starter
Racer
Joined: Aug 2014
Posts: 400
Likes: 28
From: St. Paul (smokey!) MN
NO...you have to hit the reset button...
heres a thought...start with a full tank...write down the mileage...drive it until half full...go fill er up...subtract the mileage you wrote down from the present mileage at present fill up...divide the number of miles driven by the number of gallons it took to fill er up with....5th grade math...you do not need to be an engineer to figure that one out...right?
heres a thought...start with a full tank...write down the mileage...drive it until half full...go fill er up...subtract the mileage you wrote down from the present mileage at present fill up...divide the number of miles driven by the number of gallons it took to fill er up with....5th grade math...you do not need to be an engineer to figure that one out...right?
Instructor
Joined: Feb 2017
Posts: 204
Likes: 12
I had a roughly 90 mile trip and I filled up before I came back, my average was about 24-25. That was on an '03 Z06. In my standard around town driving which is a mix of highway and city, maybe 60/40 split I'm averaging a hand calculated (Not DIC) 17.4 MPG. Years ago I had a Coyote Mustang auto (yup, ugh) and it got 17.7 MPG over its lifetime that I had it. I drive the Z06 a bit harder more often since it's so much more rewarding to drive, so not bad IMO. I think I might be able to get my average up to 18+ with more time driving to average out some outlier tanks I had which were 100% start stop city traffic (on purpose to break in a new clutch).
Heel & Toe
Joined: Jul 2017
Posts: 20
Likes: 0
I've seen several threads mentioning gas mileage. I did a road trip from Lafayette, IN to Cincinnati, OH (and back). Filled up in Lafayette with 91 no-ethanol, made the trip, and filled up when I got back.
The instantaneous mileage reading in the DIC bounced around 27-30 mpg for most of the trip, cruising at about 75 for most of the way.
Calculating my mileage by trip odometer reading/refill when I got back puts it at 26.7 mpg.
Another question - over what range/period is the Average mileage calculated? I doubt it has ever been reset. Before the trip, it was saying about 22. Afterwards it said about 24. I should have tried resetting it before starting the trip, but didn't think to do that.
It appears the computer is overestimating the mileage. Is this normal? Not that I actually care - I don't expect it to be an economy car. I still think almost 27 is doing good.
'98 Vert, top up for the trip, M6.
The instantaneous mileage reading in the DIC bounced around 27-30 mpg for most of the trip, cruising at about 75 for most of the way.
Calculating my mileage by trip odometer reading/refill when I got back puts it at 26.7 mpg.
Another question - over what range/period is the Average mileage calculated? I doubt it has ever been reset. Before the trip, it was saying about 22. Afterwards it said about 24. I should have tried resetting it before starting the trip, but didn't think to do that.
It appears the computer is overestimating the mileage. Is this normal? Not that I actually care - I don't expect it to be an economy car. I still think almost 27 is doing good.
'98 Vert, top up for the trip, M6.
Melting Slicks
Joined: Dec 2005
Posts: 2,017
Likes: 169
From: SE VA VA
I'm getting about the same on my new 2018 LT1 M7, subtract 1.5 - 2 mpg from what the computer said and that's what the actual mileage was using the old division method, Dic said 30.9 mpg on the last tank, actual was about 29. Still great mileage running thru the mountains at 75mph! 😀
Take that number and the mileage from the odometer. Do the math.
To the C5, best I've seen on mine was 34 over about 600 mile round trip.
(29-31 in the 7)
Given my daily commute is 8 miles round trip, or 16 mi if I go home for lunch, my typical average is about 15.5 in the C5 and just under 17 in the C7.
Melting Slicks
Joined: Jul 2010
Posts: 2,793
Likes: 333
From: Leesburg Fl
2018 C5 of Year Finalist
St. Jude Donor '14,'18
I try very hard not to sound like an engineer... Trying to use simple analogies and non technical jargon will only help people understand.. Its not about how much I know, or trying to show what I know. its more about transferring the knowledge to others so they understand it. One of my greatest pleasures was teaching engineering to 4th and fifth year engineering co-op students. When the light actually went off in their heads understanding an engineering principle, I could see the joy in their faces.. Very rewarding.. I've come here to try to give some insight into this car. as humbly as possible.. some embrace that, and others seems to feel intimidate by it in the form of disrespect.. the reason for so many train wrecks driven by my own hand. IM not the mean and miserable person some make me out to be.. Ill help anyone if I can, I don't clam to know it all as some suggest.. I also do not take any disrespect from anyone.
Bill aka ET
Bill aka ET
By the way, I learned that newspapers write in 8th grade reading level. Maybe that info will help.
Team Owner
Joined: Mar 2001
Posts: 21,325
Likes: 3,841
From: small town in S.E Pa. PA
St. Jude Donor '03-'04
I use the Denzel Washing to rule of thought when it comes to reaching people.. Denzel said in a movie " explain it to me as if I was an eight year old." sage advice that I bring to the class room and to no only this forum but to others.. it does no one any good if you explain in a manner that only engineers can understand.. Many smart people understand this .. they will get the low key version and so will those with little technical skills. in either case the lesson is usually understood.. Again I've never tried to show brilliance but just having the knowledge is somehow read by some as being self serving.. .
Melting Slicks
Joined: Sep 2011
Posts: 3,498
Likes: 680
From: The beautiful Alabama Gulf Coast!!
Evil-Twin -- is it true then that the average fuel economy calculation is based on the last 18 gallons or so used unless it's been reset as the owner's manual suggests?? Thanks.
Last edited by Mickeyrx70; Aug 7, 2017 at 03:20 AM.