Fuel mileage question
Thread Starter
5th Gear
Joined: Nov 2011
Posts: 5
Likes: 0
From: Oakley CA
Fuel mileage question
I just bought a 2001 C5 coupe, manual 6-speed, 5.7 V8 with 62,560 miles. The dealer filled it up for me and when I found the fuel range button, it said 164 miles. I saw somewhere that it has an 18 gallon tank. The original window sticker says it gets 19 mpg city and 28 highway. How is it possible that I can only go 164 miles on a full tank? I have put about 40 miles on it and it's down a 1/4 tank. Is there something wrong here and if so, what can I do to fix it? 
Drifting
Joined: May 2010
Posts: 1,482
Likes: 2
From: Pearland, TX
It calculates the mileage based on the amount of fuel used and the distance driven recently. If it thinks you're only getting 164 miles on a full tank, then that means somebody was doing burnouts in the parking lot with it just before they filled it up.
Tech Contributor
Joined: Dec 2003
Posts: 19,384
Likes: 87
From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
The fuel gauge is notoriously unreliable. Did the gauge drop quickly to 1/4 contents or travel down smoothly? It could be a gauge error.
The DIC/gauge take contents from the senders in the fuel tank so if its getting a bad reading of contents, all the DIC calculations will be wrong.
Fill the car to full again and do a manual check of the gas mileage. You should get about 18-20 around town (about 300 miles range). You're correct that the two tanks combined take 18 gallons although putting in about 15 is normal. A quick manual check should show if its a gauge problem. If so, buy some Techron fuel system cleaner and run it through the tank.
If you really are getting less than 10 mpg, either you're having a great time or there's a problem.
The DIC/gauge take contents from the senders in the fuel tank so if its getting a bad reading of contents, all the DIC calculations will be wrong.
Fill the car to full again and do a manual check of the gas mileage. You should get about 18-20 around town (about 300 miles range). You're correct that the two tanks combined take 18 gallons although putting in about 15 is normal. A quick manual check should show if its a gauge problem. If so, buy some Techron fuel system cleaner and run it through the tank.
If you really are getting less than 10 mpg, either you're having a great time or there's a problem.
Last edited by DeeGee; Nov 17, 2011 at 02:56 AM.
Instructor
Joined: Nov 2011
Posts: 182
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From: Palm Harbor Fl
Whenever you fill up it's recommended to reset your average MPG on the display. If the car was driven on very short trips or driven hard each time it was started your average MPG may be very low and thus effecting your range. With some spirited driving, cruising on the weekends and driving to work in traffic during the week I manually calculated almost 18mpg when I filled up.
Last edited by Deviant LS6; Nov 17, 2011 at 03:26 AM.
Intermediate
Joined: Aug 2008
Posts: 36
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i have a 6 sp 2001 conv. most of my driving is 20 miles each way to and from work. my average MPG since May is 29.8. i rarely get less the 500 miles per tank.
Vettes commonly have fuel gauge issues. Techron really does work.
Vettes commonly have fuel gauge issues. Techron really does work.
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Even though the dealer supposedly filled the car up, did the gas gauge actually show that it was full? If not, that could be your problem. The C5 has some issues with sulfur building up on the fuel sending unit and causing erroneous readings. If it did not read full, try putting some Techron in the gas and see if that clears the sending unit. If it did read full, then try clearing out the info on the DIC and see what it reads then.
Racer
Joined: Jan 2005
Posts: 488
Likes: 2
From: Fort Lauderdale Florida
Whenever you fill up it's recommended to reset your average MPG on the display. If the car was driven on very short trips or driven hard each time it was started your average MPG may be very low and thus effecting your range. With some spirited driving, cruising on the weekends and driving to work in traffic during the week I manually calculated almost 18mpg when I filled up.
Did the reset this morning a couple of times in to work and it jumped up to 18.1
Stress immediately went away.Thanks for tip!!!
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Racer
Joined: Oct 2010
Posts: 474
Likes: 0
From: Bishop CA
I've been going crazy trying to up my gas mileage - dealership BG44K treatment, maintenance on Vararam filter, cleaned MAF & TB, new plugs & wires and finally a dyno tune. DIC still reading 12.3 MPG
Did the reset this morning a couple of times in to work and it jumped up to 18.1 Stress immediately went away.
Thanks for tip!!!
Did the reset this morning a couple of times in to work and it jumped up to 18.1
Stress immediately went away.Thanks for tip!!!
Melting Slicks
Joined: Jun 2010
Posts: 2,169
Likes: 1
From: Buford Georgia
easy fix...
it says 164 cause it is calculating by ur current "avg mpg"
scroll through untill you find the avg mpg. it will prob be a low number. in the teens if its full at saying 164 range.
once u found the average mpg. hit the reset button. drive down the road/hwy for a 20 seconds. when you see the avg # go up on the dash that what it was before, you will see the range shoot up as well..
Hope that made since and Good Luck!
Matt
it says 164 cause it is calculating by ur current "avg mpg"
scroll through untill you find the avg mpg. it will prob be a low number. in the teens if its full at saying 164 range.
once u found the average mpg. hit the reset button. drive down the road/hwy for a 20 seconds. when you see the avg # go up on the dash that what it was before, you will see the range shoot up as well..
Hope that made since and Good Luck!
Matt
Safety Car
Joined: Sep 2005
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From: Southeast, Tennessee
St. Jude Donor '09 thru '26
I've been going crazy trying to up my gas mileage - dealership BG44K treatment, maintenance on Vararam filter, cleaned MAF & TB, new plugs & wires and finally a dyno tune. DIC still reading 12.3 MPG
Did the reset this morning a couple of times in to work and it jumped up to 18.1 Stress immediately went away.
Thanks for tip!!!
Did the reset this morning a couple of times in to work and it jumped up to 18.1
Stress immediately went away.Thanks for tip!!!
Racer
Joined: Jan 2005
Posts: 488
Likes: 2
From: Fort Lauderdale Florida
sarge, the DIC is notoriously inaccurate. full the car up. note the odometer reading, drive for a bit (a few days if it is your dd or the weekend if it isn't, then go back to the same station you filled up at, at approximately the same time and fill up again. do the simple math and you'll have a much more accurate idea bout your fuel mileage. BTW, we are neighbors. i'm in hollywood. nice to meet you.
Racer
Joined: Jul 2010
Posts: 262
Likes: 0
From: Jefferson City Missouri
You are in a panic way to early! Take a few deep breaths and manually check the mileage as suggested above. I have an 02 which gets 29.8 mpg with me taking no special care to get better mileage. Anything under 20 to me means you are running the hell out of it, or the car has a low geared rear in it, or major engine work for added hp.
Pro
Joined: Oct 2010
Posts: 564
Likes: 12
From: Vancouver British Columbia
I have a '02 C5Z with 9k. miles, only premium fuel, always in tip top tune, driven very easily, city/hwy combined do I rarely get more than 18 mpg., 350 miles on a full tank of gas, 29.8 mpg avg., is econo car territory, how is that possible? My son also has an '02 Z and his mileage is almost identical to mine.
Racer
Joined: Jul 2010
Posts: 262
Likes: 0
From: Jefferson City Missouri
Econo car territory on a vett is possible for a combination of reasons but your first tip off comes from looking at the tac at 70 mph. On a standard with a 6 speed you are doing 1400 to 1500 rpm. while the typical 4 cyl rice burner is running upwards of 2000. They need the rpms to have power enough to pull hills and generally operate on the highway. A vett has a powerful engine that will pull the car easily on the highway and allows for use of a fairly high geared rear end while running at slightly over an idle. The vett. idleing with minimal load uses minimal fuel while the rice burner is running a higher rpm and under more load. However, with the minimal weight and lower gearing the econo with a 2.0 or less engine can still pull some good mpg numbers. BUT THEY JUST DON'T LOOK GOOD DOING IT LIKE WE DO!
Pro
Joined: Oct 2010
Posts: 564
Likes: 12
From: Vancouver British Columbia
Econo car territory on a vett is possible for a combination of reasons but your first tip off comes from looking at the tac at 70 mph. On a standard with a 6 speed you are doing 1400 to 1500 rpm. while the typical 4 cyl rice burner is running upwards of 2000. They need the rpms to have power enough to pull hills and generally operate on the highway. A vett has a powerful engine that will pull the car easily on the highway and allows for use of a fairly high geared rear end while running at slightly over an idle. The vett. idleing with minimal load uses minimal fuel while the rice burner is running a higher rpm and under more load. However, with the minimal weight and lower gearing the econo with a 2.0 or less engine can still pull some good mpg numbers. BUT THEY JUST DON'T LOOK GOOD DOING IT LIKE WE DO!
Last edited by tak06; Nov 18, 2011 at 03:20 AM.
Melting Slicks
Joined: Jun 2010
Posts: 2,809
Likes: 3
From: Yorktown Virginia
You're assuming that I am driving in the city in 6th gear to get 29 mpg? not realistic. I'm talking avg. city/hwy real world of 18 mpg that I'm getting, yes I probably could achieve 30 mpg all hwy in 6th gear, but to avg. 29 city/hwy is a stretch. To say that fuelling a 5700 cc engine at 1400 rpm's vs 2000 cc's at 2000 rpm's would be equal in fuel economy is unbelieveable.
Racer
Joined: Jul 2010
Posts: 262
Likes: 0
From: Jefferson City Missouri
You're assuming that I am driving in the city in 6th gear to get 29 mpg? not realistic. I'm talking avg. city driving of 18 mpg that I'm getting, yes I probably could achieve 30 mpg all hwy in 6th gear, but to avg. 29 city/hwy is a stretch. To say that fuelling a 5700 cc engine at 1400 rpm's vs 2000 cc's at 2000 rpm's would be equal in fuel economy is unbelieveable.
Last edited by Buggyman; Nov 18, 2011 at 10:18 AM. Reason: To insure accuracy
