Mpg Question

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Jun 15, 2007 | 02:01 PM

#21

Cobraboy

Racer

Joined: Jan 2007

Posts: 314

Likes: 36

From: Bolton Ontario

I have definitely found that my DIC is not accurate (hmm...that sounds a bit rude). Of course being a Canadian car, there is a further complication since the DIC gives MPG and that is US gallons, not Canadian gallons. Canadian gallons are 1.20095 X larger than a US gallon.

Calculating the gas mileage manually is very accurate, provided you do several tankfulls in a row. No good doing one every now and then since you may have more in one tank than the next. Also, getting 40 MPG for a 5 minute highway stretch is kind of meaningless when you get 15 blasting your way there and back.

Here are my numbers for 5 tankfulls in a row. I do probably around 70% city driving and 30% highway, but it's hard to say. Stop and go traffic on a highway doesn't really count as highway mileage in my books.

DIC indicated an average for all 5 tanks of 9.8 L/100kms. This works out to 28.7 mi/gal (Canadian) or 23.9 mi/gal US. Working out the mileage from the distance travelled and the gas used, I got 26.2 mi/gal Can or 21.8 mi/gal US. That's a significant error in the DIC indication.

Rick

Jun 15, 2007 | 04:10 PM

#22

Oldvetter

Le Mans Master

Joined: Feb 2002

Posts: 6,937

Likes: 21

From: Waldorf MD

I average 22.5 mpg going to work (20 miles, urban with few traffic lights) and I have gotten 32+ mpg on trips to beach (flat highway).

I did check DIC with calculations, it is a little optimistic, but close enough.

BTW, there is no fuel flow sensor(s) (with return line there would have to be two), the computer uses fuel injection pulses to calculate mpg. Talk about adding up drops!

Jun 15, 2007 | 05:36 PM

#23

tiojames

Team Owner

Joined: May 2005

Posts: 23,682

Likes: 9

From: Flagstaff Az.

Got 31 on trip home from Fla. to Az.(2000miles) with car when I bought. That was actual miles divided by actual gallons. Got the same when I took it to A&A for mods(500 miles). Both trips were 80MPH trips for the most part. Car was an auto with 3:15s. With all the mods(see sig) it now gets 28 at 80-85. Friend of mine in Fla. has an 02 a4 and gets 30-32 at 75-85 with his 2:73s. I have found the computer to be off about 1 MPG on the high side.

Last edited by tiojames; Jun 15, 2007 at 05:38 PM.

Jun 15, 2007 | 05:39 PM

#24

SLO C5

Race Director

Joined: Aug 2006

Posts: 13,542

Likes: 1

From: Are you fat because you're lazy or lazy because you're fat? San Jose, CA

Cruise-In X Veteran

St. Jude Donor '09

If I just cruise at 70 in 6th gear I can get 30mpg, but that isn't any fun. I will say, however, that since adding the 19x10 and 19x13 I have seen a noticeable drop in MPG. But who gives a hell, the car looks sick and has traction all day.

Jun 15, 2007 | 08:40 PM

#25

steves65korvette

Thread Starter

Racer

Joined: Feb 2006

Posts: 426

Likes: 0

From: tx

Thanks for all the replies ! I will check my mileage again when I take a longer trip with more highway miles. I had a few stops the last time on a trip of about 160 miles.
Suprising to me too is that a lot of the mods do not seem to really hurt the mileage a great deal... Not true in the old days....
Steve

Last edited by steves65korvette; Jun 15, 2007 at 08:43 PM. Reason: add

Jun 15, 2007 | 11:01 PM

#26

Tom73

Race Director

Joined: Apr 1999

Posts: 15,143

Likes: 477

From: NM

Quote:

Originally Posted by DefenderC5

How do you figure? The pump shuts off at pretty much same time since the federally mandated vapor recovery/over flow prevention systems are all pretty regulated.

Not around here. I seldom see a vapor recovery/over flow system. If I run into them I try to wait until the next town if I can. When I have to use them they can short me several gallons.

Quote:

Originally Posted by DefenderC5

I found the most accurate system is to:

1) Reset Trip meter during last full fillup
2) At next fillup, divide the number of miles on the trip meter since last fillup by the number of gallons needed to fill tank.

The key is to refill the tank to the same exact point as last time. That is very hard to do. A half gallon difference can have a huge impact on MPG. For the manual system to work very well you have to run it over several tanks of gas to keep the full factor to a minimun. So to get good highway mile info you need to be traveling about 2,000 miles. That should give you enough tanks to average it over.

On a trip from Austin TX to Las Vegas I averaged 30.5 mpg. That was directly to LV and back. About 2,000 miles. On a later trip to LV took side trips to Santa Fe and Taos NM and to the Grand Canyon. The mountains took their toll, only got 29.5 mpg.

Sure is nice having a car like the C5 that is an economy car

tom...

Last edited by Tom73; Jun 15, 2007 at 11:04 PM.

Jun 15, 2007 | 11:39 PM

#27

Rickyh93

Pro

Joined: Sep 2006

Posts: 571

Likes: 0

From: Milwaukee Wi

I checked mine from Atlanta to Milwaukee and averaged just over 28 in my 01 z with 68k miles on it. That was doing about 80-85 the whole way with the heater on it was in December when I drove the car up here.

Ricky