When my car was new, I was told by many here to wait awhile and the N* engine will loosen up and perform better. At 9000 miles It does wind out quicker and feels smoother than ever. What I did not expect was how the gas economy keeps rising. Where I once couldnt get the MPG to go over a pitiful 14. I am now getting 17+ on the country roads here, and a round trip to Cincinnati (1200miles) all highway came in at 23.7 MPG. I was wondering if anyone else noticed a difference as the car gains miles.

My old boss had a newer STS with a 4.6 northstar, he said it gained 50hp after the first 6 months....It seems to be a trend with the northstars

I have noticed a considerable difference. When I first got the car I would average about 17+mpg, pretty good considering the stop and go traffic I encounter every day. Now, many thousand miles later, I average about 23+mpg.

I too have noticed a significant increase in gas mileage. I currently have 32k km (roughly 20k miles). On one of my trips to the lake before I parked the car for the winter, according to the DIC I was getting 9.5l/per 100 km, just about 25 miles per gallon. I was using the cruise control for most of that trip.

My father had noticed the same thing with his '98 STS. He started with an avg. of 20-21 mpg city/highway, and now he'* been getting 24-25.

definately! It'* completely normal and to be expected. Granted I don't have the 4.6, but I've seen as high as 36 MPG average on a 100 mile trip on the highway. As your mileage gets higher, up to maybe even 15,000 miles, you'll probably see more subtle change in economy as well.

I got mine at about 25k miles but I have noticed running on premium I get averages 19-21.5 mpg in the CITY. And I live in a hilly city. That improved from 14 city when I first got it as I suspect it was run on regular. About three weeks after buying it and using premium I noticed the increases. It rapidly increased from 14 to 17 and then slowly up, up ,up. I suspect it has plateaued at about 20 city. I went for a ride on a hilly interstate and got 26.5.

I'm not so lucky. My GXP is at 20,000 miles and I have always run Premium. My commute mileage is 18mpg. I just drove 180 miles, reset the mileage at 73mph, and drove straight thru with light traffic. Mileage was 21mpg. 2500rpm at 75mph.

My 2002 Impala w/ 3800 was getting 29-30 on the road, and an average of 28 during my daily 30 mile commute. 2000rpm at 75mph.

My V8 Camaro gets 25mpg on the road. 1800rpm at 75mph.

the last trip i took..

I filled up at home the night before with light traffic at 120 kms i drove from Cornwall to Oshawa
230 miles i filled up at the service center only cause my budy needed gas i figured WTF
from there i went another 50 miles then drove all the way home 280 miles had half a tank when i got here.

so from what i can figure is that works out with 90 liters of fuel purchased i drove 560 miles i should have gotten 28.29 mpg but i only used 70 liters of fuel so really i got 32.47 mpg mmmm anyways My GXP rocks on the MPG stage lol i know i didnt and couldnt have gotten 32.47mpg but eh! lol

amd of course, the related question is, what can be done to increase fuel efficiency? I do get the distinct feeling that we are living at the very end of the petroleum/high performance car era. In another 20 years, we'll be driving electric scooters and WV will have an Atlantic coastline!