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Fantastic gas mileage on highway trip - 2008 DTS

15K views 42 replies 15 participants last post by  jazoo 
#1 ·
My car got 33 MPG on my trip to and back from Alabama this weekend. I was by myself and not carrying a heavy load or anything, but I still think that's pretty remarkable.

I know part of the reason for the great mileage is the fact that I put ethanol-free 93 octane gas in it. This makes a noticeable difference just driving around home, getting me 20 MPG instead of 17 MPG that I get with 10% ethanol 87 octane. But 33 MPG on the highway is a huge jump that I did not expect.

I also kept it at 65 MPH on the interstates, which helped I'm sure. I like that speed not only for the better fuel mileage but because it's just more relaxed since you don't have to worry about passing nearly as much.

I know there's debates about how much advantage you get by putting the ethanol free and/or premium gas in these engines, but I can attest at least in my own experience that it makes a significant difference. Yes, the price per gallon is going to be more, but I've done the math and in my area getting 20 MPG instead of 17 MPG makes up for the price difference. The cost per mile ends up being about the same.
 
#37 ·
I'm back.

Believe it or not I actually forgot about this on the way down to the beach (it was a crazy morning and day), but I did remember to reset all fuel related DIC readings right after I filled up in Myrtle Beach. When I got home, I took pictures:





As I anticipated, having the car loaded down with the extra passenger and luggage along with having to traverse the mountains brought down the MPG. But, I'm still quite pleased with 28.5 MPG all things considered. If you take the mileage and divide by the fuel usage manually, it actually works out to be slightly higher @ 28.8 MPG. Either way, as I said, I'm rather pleased and it's something I never expected with this car.
 
#43 ·
Believe it or not I actually forgot about this on the way down to the beach (it was a crazy morning and day), but I did ........ home, I took pictures. ................As I anticipated, having the car loaded down with the extra passenger and luggage along with having to traverse the mountains brought down the MPG. But, I'm still quite pleased with 28.5 MPG all things considered. ...... slightly higher @ 28.8 MPG. Either way, as I said, I'm rather pleased and it's something I never expected with this car.
rebel7254, Congratulations, that you were consistently getting ~28.5 MPG with your style of driving and where & how you were filling up the tank. We are never going to come to a solid conclusion on this issue as there are too many variables associated with this subject matter.

Anyway, I applaud your persistency.
 
#38 ·
Your 2008 "DTS" - what is the 8th character of the VIN ?

I don't think we ever determined if your car has a 3.71 or 3.11 final drive - and most of the Devilles (base, DHS) with the 3.11 see 27, 28, 29 mpg on the highway, long term, with ease.

The acronym "DTS" for the new replacements to the Deville line is misleading because originally DTS meant the performance model, had the 3.71 final drive, and were lucky (like the STS) to get 25 mpg open highway.

Glad the trip went well - We're headed from here to Myrtle Beach on 2 October - 4 day submarine crew reunion. For me, it's a 9 hour drive.

Play with this for a while - but, as I posted before, using straight gas or E10 in either the car or trucks makes no difference in mileage for me -

http://pure-gas.org/index.jsp?stateprov=MD
 
#40 ·
No problem - ALL the VIN Y cars will beat a VIN 9 car in the gas mileage department.......... but the original 300hp/3.71 DTS association dies hard.

There was a mileage thread in Seville a few years ago, with spreadsheet figures - for an ESC on a long trip .......... that one got just about 30 mpg, including mountains, with 2 people and some luggage.
 
#42 ·
No problem - ALL the VIN Y cars will beat a VIN 9 car in the gas mileage department.......... but the original 300hp/3.71 DTS association dies hard.

There was a mileage thread in Seville a few years ago, with spreadsheet figures - for an ESC on a long trip .......... that one got just about 30 mpg, including mountains, with 2 people and some luggage.
My 01 seville would always see 31-33 mpg cruising 65 mph. I loved it. Still gets about 29ish. 130k that car still rides and runs awesome
 
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