2001 Corvette
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Heel & Toe
Joined: Aug 2009
Posts: 21
Likes: 0
2001 Corvette
I have noticed in the last week that my C5 has dropped way down on gas mileage.It runs like a top,no skip,runs smoothly just terrible gas mileage.Could this be a bad oxygen sensor ? Anybody have any idea what it could be ?
Drifting
Joined: Apr 2000
Posts: 1,390
Likes: 36
From: INDIANA
Could be an O2 sensor, they don't always throw a code, but may richen substantially enough to effect mileage. If its the sensor, better fix it pronto, cause extra rich will kill a catcon pretty soon.
Tires can cost you a couple of mpg, but 8 is a stretch. I lost approx. 2 mpg of highway when I changed from the GYSC to Firehawks.
Dragging brakes or a wheel bearing going bad can do that also, but I don't think the wheel bearings are a troublespot on C5's usually. (Blazers, oh yeah).
Tires can cost you a couple of mpg, but 8 is a stretch. I lost approx. 2 mpg of highway when I changed from the GYSC to Firehawks.
Dragging brakes or a wheel bearing going bad can do that also, but I don't think the wheel bearings are a troublespot on C5's usually. (Blazers, oh yeah).
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
Switching from the OEM Runflats to regular radials will decrease your mileage about 3 mpg (one magazine found 3.3 mpg change). Winter driving also loses mileage (gas additives, denser air, and longer warm-up times).
Last edited by Oldvetter; Jan 31, 2011 at 09:48 PM.
Le Mans Master
Joined: Feb 2003
Posts: 6,683
Likes: 144
From: Memphis Tennessee
Both are true....especially the winter-blend fuels with high levels of Alcohol
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St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
Tech Contributor
Joined: May 2008
Posts: 3,100
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From: Somers, CT and Clermont, FL
St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
Le Mans Master
Joined: Aug 2005
Posts: 5,375
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From: CA.
St. Jude Donor '13-'14-'15
Are your NEW tires a BIGGER size ?? If so then it's just that your speedo is off and needs to be corrected--OR your old tires were SMALLER that stock and now you installed stock tires---
Even a tire that is only 1" taller on a C5 will make your speedo 5% off --so at 70 it's 3.5 MPH off----2" diff would be 10% off--so 7 MPH at 70
But to be 7 MPG's off it would have to be a combination of many things-- IF you aren't getting any codes
1. make sure you had the fuel meter set to ENGLISH and not METRIC
when you were getting 31 mpg
2.If you recently dis connected your battery or it went very low--Your fuel trims will all have to learn out again--the more modded your engine is the longer it takes
3. If you recently cleaned your air filter and re-oiled--you may have over oiled it--clean the MAF with brake clean
4. make sure you didn't leave any hoses or lines off the intake anywhere
5. your ECM may be in "Open Loop Fault" for a random 02 issue--clear the codes EVEN IF there aren't any showing or you have no chk eng lite-
Even a tire that is only 1" taller on a C5 will make your speedo 5% off --so at 70 it's 3.5 MPH off----2" diff would be 10% off--so 7 MPH at 70
But to be 7 MPG's off it would have to be a combination of many things-- IF you aren't getting any codes
1. make sure you had the fuel meter set to ENGLISH and not METRIC
when you were getting 31 mpg
2.If you recently dis connected your battery or it went very low--Your fuel trims will all have to learn out again--the more modded your engine is the longer it takes
3. If you recently cleaned your air filter and re-oiled--you may have over oiled it--clean the MAF with brake clean
4. make sure you didn't leave any hoses or lines off the intake anywhere
5. your ECM may be in "Open Loop Fault" for a random 02 issue--clear the codes EVEN IF there aren't any showing or you have no chk eng lite-
Heel & Toe
Joined: Aug 2010
Posts: 23
Likes: 0
From: Reston Virginia
I have noticed a pretty severe drop in mpg as well.During the summer I was getting around 320+ miles on a tank. Now im lucky to get 270 miles on a tank.. 
I use the vette as a DD and its 90% city driving.
I use the vette as a DD and its 90% city driving.
Race Director
Joined: Jan 2006
Posts: 10,554
Likes: 33
From: Not on either liberal coast.
The obvious...tires loose air pressure in the winter months. Those new tires might not be inflated to the correct air pressure. Under inflated tires can decrease fuel economy.
Check the air pressure and adjust according to what's on the drivers door, not what's on the tires.
Check the air pressure and adjust according to what's on the drivers door, not what's on the tires.