Drove from NJ to NC today, I checked the gas mileage using the old fashion way (fill up gallons divided my mileage) and checked it with the DIC. I refilled with the gage showing just about 1/2 tank remaining.

I was driving about 50/50 highway/city, (436 miles) DIC said average speed was 42 mph.
Here is what I got with 2 top-off/fill-up's:

1. 211 miles / 9 gallons = 23.5 mpg. The DIC said I got 24.2 almost a 1 mpg different.

2. 225 miles / 9.1 gallons = 24.7 mpg. The DIC said I got 25.2, about a 1/2 mpg different.

My CTS is 263hp Auto/RWD w/18" wheels w/4400 miles.

Only going around 190 miles tomorrow, then another 350 on Friday, I'll keep you posted on the mileage. :)

The computer always seems to be a little optomistic, but if it's within 1 mpg, that's still pretty close. Your mileage seems to be pretty good for mixed driving. You should probably be in the high twenties if majority is highway. Other vehicles I've owned, with computer, seem to validate your differences; haven't had my STS long enough to get a average mpg on a trip yet. Thanks for sharing your numbers.

Thanks, LFG.

With almost 2000 miles on my CTS, I've found that the DIC consistently overstates fuel economy by about 0.5 MPG (DIC 17.8 vs. 17.3 ACTUAL) in mostly city driving. I usually reset the DIC and refill the tank at intervals of 12 to 15 gallons 87-octane Shell "top tier" gasoline.

Hmm... 23-24 mpg on the way to Key West? That's a little better than the 19.2 avg the DIC says I'm getting I'm getting with my FE2 AWD around town in the snow and ice of the midwest. Need a co-pilot?

I drove around 200 mixed miles today, but haven't filled the tank yet. The DIC is reading 26.9 mpg, I'll get the real number's when I fill up. I think it will be around 26mpg or more. ;)

Just out of curiosity, how fast are you driving on the highway?

Just out of curiosity, how fast are you driving on the highway?

I stay around 5 over the speed limit & use the cruise. Highway was 55-70 mph. The first day the DIC said average speed highway/city was 42mph.
I won't be driving again untill tomorrow and I will post when I fill up. ;)

Update with mixed driving.

340 miles / 13.2 Gallons = 25.8
Car DIC said 26.3.......1/2 mpg different....not bad. :thumbsup:

I drove mostly highway today and when I fill-up tomorrow I will post the numbers.

Drove from Atlanta o Virginia today. Some 340 miles. Mostly 65 to 75 mph. At the arrical in the hotel the computer showed 28.6 mpg.....could not believe it, but it was true. Oh, CTS has 7,000 miles on the odo. It seems to me that the engine is loosening up, it is becoming more responsive and the fuel economy is getting better.

Normally it takes 12000 miles for an engine to be fully broke in and fuel economy to peak.

Well, the VQ engine did the same thing. Only it didn't slowly get better. It seemed to be so-so with no change until people got "around" 10,000 miles and then it jumped maybe 2 MPG on the Hwy. After that I had an average of 24.3 MPG running 5 over over on the interstates. And that is running Premium gas.

I will be thrilled if I can match LFG who's running about 26 or Mofex who is running about 28 MPG.

Are these with Regular gas?

I really like this car.

I did my last run yesterday before the return in 2 weeks. After a 400 plus mile run, about 80% highway I got 27mpg (my numbers) and the DIC info mpg was 27.3 & average speed of 68 mph.

Yes reg. gas.

OK, update.
Drove back home yesterday, some 340 miles. The average speed – 67.8 mph, fuel economy – 26.6 mpg. Why the difference (driving up to Virginia the fuel economy was 28.6 mpg)? Not sure but here are some factors that could have influenced this:
1. going up the temperature was 60deg, coming back – 40F to 28F.
2. traffic: going up – very smooth drive, back – in at least two places traffic was heavy with some stop-and-go sections (I could see the mileage drops).
3. wind – coming back I was against quite strong head and side wind.
4. Gas: going up – QT in Atlanta, coming back – Exxon in Virginia. Not sure about the winter mix…
5. Tire pressure – affected by ambient temperature. According to TPMS the pressure was 2 psi higher driving to VA.
I am very happy with the gas mileage. In the end it is a performance car and I did not expect great fuel economy.

OK, update.
Drove back home yesterday, some 340 miles. The average speed – 67.8 mph, fuel economy – 26.6 mpg. Why the difference (driving up to Virginia the fuel economy was 28.6 mpg)? Not sure but here are some factors that could have influenced this:
1. going up the temperature was 60deg, coming back – 40F to 28F.
2. traffic: going up – very smooth drive, back – in at least two places traffic was heavy with some stop-and-go sections (I could see the mileage drops).
3. wind – coming back I was against quite strong head and side wind.
4. Gas: going up – QT in Atlanta, coming back – Exxon in Virginia. Not sure about the winter mix…
5. Tire pressure – affected by ambient temperature. According to TPMS the pressure was 2 psi higher driving to VA.
I am very happy with the gas mileage. In the end it is a performance car and I did not expect great fuel economy.

Are these numbers from the DIC or did you do the math yourself (miles divided by gallons used)? The DIC can be off by up to 1mpg.

DIC, but they are very close to reality.