I had a 2005 DeVille and consistently got 25 MPG or more on long trips. I thought I would get the same mileage on my 2008; maybe even better because of the larger tires but I'm getting less. I thought that now that they use Mobile 1 oil it would stay the same. The owner's manual says to use premium and I did for a short time and then changed to regular and saw no difference in power or gas mileage.
... I thought that now that they use Mobile 1 oil it would stay the same. The owner's manual says to use premium and I did for a short time and then changed to regular and saw no difference in power or gas mileage....
I have also tried premium fuel and synthetic oil. After trying that and keeping track of my mileage, I now use regular fuel and conventional oil.
I'm sure that in a lab environment, the premium fuel and synthetic oil make a measurable difference (maybe 1 or 2 MPG), but for my wallet, the difference is not meaningful.
Superjim, I was getting as high as 26 and 27 MPG in my Deville on a long trip. I have over 6K miles on the 08 so it's certainly broken in. I think a drop from 26 to 22 on a long trip is significant.
Superjim, I was getting as high as 26 and 27 MPG in my Deville on a long trip. I have over 6K miles on the 08 so it's certainly broken in. I think a drop from 26 to 22 on a long trip is significant.
yes... that much of a drop is significant. It should get better than that.
I rented a 2006 DTS for two weeks, before I bought mine. It got around 25, even the way I drove it.
I have had 2007 DTS's for loaners from my dealer. I have put a lot of miles on them. They usually got around 25 on the highway.
My Performance Sedan will get 21/22. If I drove easier, it could possibly get better than that. But I very seldom drive the speed limit on the highway. Usually 80/90 is my highway speed. It will get 21 all day at 80/90.
My Performance Sedan will get 21/22. If I drove easier, it could possibly get better than that. But I very seldom drive the speed limit on the highway. Usually 80/90 is my highway speed. It will get 21 all day at 80/90.
Texas Jim
In my '98 and prior DeVilles, at that speed I could still average 30 mpg on the open road. But with the 2000 redesign, Cadillac reworked the N* to run on regular unleaded and made some tweaks to the transmission as well resulting in the lower mpg figures.
Jim, keep in mind that in your performance model the transmission has Performance Algorithm Shifting, and is geared differently than the transmission in the Lux I-III models.
My '06 Lux III consistently averaged 17.5-18 mpg in all city driving, the '07 loaner I've been driving the last month has yet to break 17 and I've been babying it since its not mine.
Jim, keep in mind that in your performance model the transmission has Performance Algorithm Shifting, and is geared differently than the transmission in the Lux I-III models.
My '06 Lux III consistently averaged 17.5-18 mpg in all city driving, the '07 loaner I've been driving the last month has yet to break 17 and I've been babying it since its not mine.
Right... I understand about the different gearing between the LUX models and the Performance Sedan. ( I really like the way the Performance Sedan RUNS.. but I wish it would get the mileage the LUX models do.)
That was why I pointed out the difference in mine and some of the loaner DTS's I have driven. I have put quite a few highway miles on some of them.
The LUX models ALWAYS get quite a bit better mileage than mine does.
there may be a reason for your fuel economy difference.. one thing to check before anything is go to fueleconomy.gov, this website gives the laatest in fuel economy standard for each vehicle, it supercedes manufacturers specs as to what you should be getting
This is an interested web site but I'm talking about calculated MPG and not EPA estimates. I did notice that the throttle response is different. It takes a lot let pressure on the gas pedal to accelerate. I think between 2005 and 2008 Cadillac went from mechanical throttle control to electronic. My 02 and 07 Vettes both had electronic throttle control but they don't seem as "twitchy" as the Cadillac.
Something that may be worth verifying: are you using the vehicle calculation or are you calculating it manually?
The reason is that, believe it or not, the formulas used to determine MPG in trip computers has changed in some cases. You would think there is nothing to argue over, but there are points of contention. For example, some vehicle trip computers do not add in fuel used while you are idling in Park while other vehicle trip computers do. (Try this experiment - leave your vehicle idling for an hour and see if your reported MPG changes at all. Some vehicles will reflect no change in MPG - a dead giveaway that they don't add in the fuel used during vehicle idling.)
In addition, if you are using the vehicle trip computer, the calculation is based on variables such as injector pulse width and throttle position, not the fuel tank level. In other words, if a vehicle is old, this calculation could start to become inaccurate as injectors and fuel pumps start to misbehave.
If you want a completely apples-to-apples comparison, you have to do the calculation by hand using the trip odometer and the gas pump.
