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2007 DTS LuxII, 2008 GMC 2500HD Crew Cab 4x4, 2002 Seville SLS (RIP)
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81 Posts
Discussion Starter #1
So over this last few weeks with the warmer tempetures I have been checking mileage. I drive 36 miles a day in rush hour back and forth to work with an average speed of 55 MPH. That combined with some light errand running I am getting 20 MPG which kind of surprised me. This weekend the wife and I ran up to the casino about 176 miles round trip. I held the speedo at moderate but consistant 73 MPH. Checked mileage when we got back in town today and I am getting 24 MPG. I was hoping for better but I seem to remember it said here that beyond 55 - 60 MPH mileage takes the downturn.

So my question is what is the best mileage some of you have gotten with your SLS/STS or Eldo? And what speed are you driving in your highway driving bandwidth?
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,481 Posts
Above 50 mph the fuel mileage begins to drop due to air drag = more gas pedal required to maintain speed.

The mileage differences between the SLS with a 3.11 final drive and a STS with the 3.71 final drive are substantial.

Let's not talk about city/near suburban mileage - that varies all over, from 11 mpg to 18 mpg.

We have several reports of 29 mpg in a 2000 or later ESC on long trips. It all depends on your foot, vehicle speed and state of maintenance.

A SLS should easily get 26 - 29 mpg at 55 mph, dropping above that. A STS should get 25 mpg at 55, dropping above that.

My 2002 STS gets 24.8 mpg long-term on the Interstates from here to Florida, including the gas and food stops and slow driving. 831 miles one way. 87 octane Top Tier fuels. Around here, semi-rural, I get 17 - 20 mpg day in and day out.
 

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White Diamond '03 DHS (with DTS floor shift)
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86,785 Posts
Do you or have you recently had an SES light on with a P0741 code? Being a 2000+, that's rather common and WILL affect you fuel mileage.
 

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2001 El Dorado ESC
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7 Posts
Checked mine Sunday, 2001 Eldorado ESC. I reset the mileage after I was on the freeway and up to speed. Over a 50 mile trip it averaged 27mpg. Mine must be doing ok. Cruise control was set at 65.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,481 Posts
Couple of things to remember - If you reset the long-term average fuel mileage it will ratchet up pretty quickly during the first highway trips and down pretty quickly during city driving. As more and more data points are stored it takes longer and longer to drive long enough, far enough to cause a decent change in long-term mileage readings. The instantaneous readout is basically useless - it quickly shows you what gas pedal changes do, and that's IT.

Look at the system this way: You fill up, reset the average, immediately get on the Interstate and drive for a half hour. Let's say the average ratchets up to 25 mpg. You get off the Interstate and are immediately stuck in a traffic jam for a half hour and fuel mileage is then 0 - so, for that hour of driving, your actual gas mileage was (and will indicate close to) 12.5 mpg.
 

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2007 DTS LuxII, 2008 GMC 2500HD Crew Cab 4x4, 2002 Seville SLS (RIP)
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81 Posts
Discussion Starter #6
My average according to the cars built in system had an average of 25 MPG but I do the formula the old school way; fill the tank to the top of the filler neck and after the trip fill it again just the same way and do the math - 24.1 MPG.
I agree that instantaneous reading is worthless.

Ranger did you happen to check on your recent trip out west - if I remember that was your daughters car right?
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
The onboard system calculates fuel mileage using exact mileage traveled and the exact amount of fuel injected. It's more accurate than any other method. Fuel expands and contracts with temperature changes, and "E" on the gauge is anywhere from empty to almost a gallon left, so you're never as dead on accurate as the onboard system is.

Also, there needs to be airspace in the tank. For expansion, and for proper EVAP system operation. Never top off the tank.
 

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2011 Crown Vic LX, 2009 Chevy Malibu 2LT
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5,607 Posts
Filling to the top of the neck will fill the vent pipe and saturate the evap canister... not a wise method.
 

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2007 DTS LuxII, 2008 GMC 2500HD Crew Cab 4x4, 2002 Seville SLS (RIP)
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81 Posts
Discussion Starter #9
Good point Drew and MC, I never thought of that - point taken and thanks!!
Its not often that I fill it to the top as my wife puts most of the gas in it but never fills it - $10 here $20 there.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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Ranger did you happen to check on your recent trip out west - if I remember that was your daughters car right?
Yes, it was her '04 SLS and I did keep track.
Avg MPG per the DIC was 25.
Per the manual method was aprox. 24
That said we were pretty well loaded and had to fight some strong winds and cross the Rockies.
 

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1999 STS - diamond white
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5,229 Posts
Yes, it was her '04 SLS and I did keep track.
Avg MPG per the DIC was 25.
Per the manual method was aprox. 24
That said we were pretty well loaded and had to fight some strong winds and cross the Rockies.
You should never drive when you are loaded :)
 

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96 seville sls
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35 Posts
Just replaced engine on my 96 SLS, remanufactured with new radiator ,water pump belts hoses etc. Came with cross threaded heads supposedly to prevent the head from ever leaking. Thanks to Samson & Sons Redmond Ore. Still only have a few thousand miles on this engine but it does seem to get less milage than previously 12.5 city 17.5 highway at 65 wish. Runs well ,no codes and Don Falgren owner of the above shop believes it will increase after the first 5k miles. FYI We have been travelling recently purchased a 2005 40 ft Alfa See Ya and have been refurbishing it as well.The caddy is basically done not much on it is original except frame and tranny,purchased a 18 ft trailer to tow the Seville behind us. Kind of coming to the close of both projects t has been fun to get both vehicles in a like new condition. My wife had followed me to a Costco and while I was inside she said several men had walked around the Seville just looking at it. I think I'm around 30 thousand or so now, hopefully that will be the end of it at least for a few years. This is not a garage kept Sunday only vehicle I drive it every day and we have taken 5000 mile trips in it. Could not have done it without my wife's support, she says if this is my mid life crisis and red fast cars is all it amounts too she's OK with it.Any way hello to everyone and take care. Jim
 

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White Diamond '03 DHS (with DTS floor shift)
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86,785 Posts
but it does seem to get less milage than previously 12.5 city 17.5 highway at 65 wish. Runs well ,no codes and Don Falgren owner of the above shop believes it will increase after the first 5k miles.
I wouldn't hold my breath.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,481 Posts
Yep ^^^

17.5 highway for a SLS is totally, completely unsatisfactory. That car should easily get 24 - 26, normally 27 - 29.

............ and after "a few thousand miles" the engine is fully broken in, so no hope there.
 

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96 seville sls
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35 Posts
We are going back to the shop in late may to get the motorhome cat 330 serviced along with the diesel gen before heading back east for a month or so.I will ask him to take a look at it.I suspect the issue is my lead foot.I love driving this car and where I can legally and safely do so I tend to use all its performance.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,274 Posts
Just replaced engine on my 96 SLS, remanufactured with new radiator ,water pump belts hoses etc. Came with cross threaded heads supposedly to prevent the head from ever leaking. Thanks to Samson & Sons Redmond Ore. Still only have a few thousand miles on this engine but it does seem to get less milage than previously 12.5 city 17.5 highway at 65 wish. Runs well ,no codes and Don Falgren owner of the above shop believes it will increase after the first 5k miles. FYI We have been travelling recently purchased a 2005 40 ft Alfa See Ya and have been refurbishing it as well.The caddy is basically done not much on it is original except frame and tranny,purchased a 18 ft trailer to tow the Seville behind us. Kind of coming to the close of both projects t has been fun to get both vehicles in a like new condition. My wife had followed me to a Costco and while I was inside she said several men had walked around the Seville just looking at it. I think I'm around 30 thousand or so now, hopefully that will be the end of it at least for a few years. This is not a garage kept Sunday only vehicle I drive it every day and we have taken 5000 mile trips in it. Could not have done it without my wife's support, she says if this is my mid life crisis and red fast cars is all it amounts too she's OK with it.Any way hello to everyone and take care. Jim
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but it does seem to get less milage than previously 12.5 city 17.5 highway at 65
check your engine RPM at speed -
sounds like you are driving in 3rd gear -
 

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'02 Eldorado ETC 85k miles / Past: '03 Deville; '02 STS
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176 Posts
I get about 15 - 17 city in my 2002 ETC with 98k miles. On the highway 6 months ago I averaged 22.0 mpg doing 75 mph on a 9 hour trip. Now I average about 21.2 mpg doing 75 mph on the 2 hour trip home everyweekend. However the roads I'm now taken are hilly and very curvy. Not flat and smooth like Houston freeways. Lol
 

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96 seville sls
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35 Posts
On the forums here are the rpm and at what speed and the car is getting the lower rpm at 65 mph for the 4th gear also I am getting reduced milage in city as well at 35mph or less. The mechanic is good people so I sure he will figure it out if its not my driving,which it may be ,just thought I could get a head start on trouble shooting this. The fuel tank was dropped cleaned and fuel pump an sensor replaced at time of engine swap
 
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