Maybe it is geared different than the other Impala you had with the same motor? What rpm are you running at 75? How does that compare with the other Impala? What if you go 70? What does the instant DIC reading say at 75 and then at 70 on flat highway. If it is geared different, it might have a different "sweet spot".

I mean, you have a situation with 2 Impala's with the same motor but different MY. So, you have weight, aerodynamics, driving style, tire inflation, etc etc coming into play overall to affect fuel economy. So something (but what?) is different. Same route, same speed, same traffic conditions, same driver, and what's left that is different? Does the new Impala weigh a little more?

Just thinking out loud here trying to help.

 

Dave B:
You might have somthing there with the tire pressure. Have always run my tire pressure on the high side. If it says 35 psi max then I'll run 30 or sometimes 32. Got my 06 Impala with 16" tires and the door sticker says 225 x 60 16's 30 psi max. My tires say 44 psi max, so I run 36 to 38psi. Not much ride difference (hey its an Impala!) but sure noticed a difference in mileage (2 to 4 + in town). Call me crazy, but it works for me (and EvansBlue, I didn't get the idea from Obama either.Started doing this when he was in {private}grade school).

 

I have 15,000 miles on it we bought it with 10,000 on it. Dealership is telling me this is what I should expect, his wifes only gets 19. I am a die hard impala driver, but this is a very tough pill to swallow.

 

The GF's 07 Impala with the 3.5 Liter - VVT V-6 is getting 27.5 (going 65 -70 mph highway) right now with "winter gas". It was a little better in the summer. I know it is a different motor than your 3.9 Liter but I drove it today and that's what it got according to the DIC. I reset it because I was curious to see what it was getting and I probably drove it conservatively because of that. Just trying to give you a comparison with a different motor but an 07 which is basicly the same car. It has 18,5xx miles on it so it is broke in for sure. I don't drive it that often though.

 

I have a long trip tomorrow, and have switched to premium gas. I will set the cruise at 70 and see how this works.

 

Didnt they get rid of Active fuel management for 08?

Im pretty sure I read somewhere that it was deleted .. and thought to myself- why would they remove it?

 

Now the GF just got home and said the average is right at 25 so I think the cold weather and winter gas is taking a toll.

 

I agree with you there Dave B. 10% (max) ethynol here in Albuquerque has sure done-in my mileage. Dropped by 2 to 3 mpg overall. Most of my miles are city so 23 or thereabouts is ok with me. Put a K&N filter in Sunday. Throttle response seems better but no real noticable change in mileage yet. Altitude is the sticking point here as we areat 5,200+ feet above sea level. Makes for poor performance in thin air conditions. What's the altitide there Salesman?

 

I have tried different speeds for long distances, @55mph I get 28 mpg, @65mph I get 25mpg and @75mph I get 22mpg. This car does have way more snap than my 06 had, so I am just going to write this off as an increase in performance (there is a noticable amount between the two) and a loss in mpg. Boss is likely not going to add any more Impala's to the fleet, I hope they have the miles per gallon increased when we replace this one in two years.

 

Yea, darn winter gas is making mpgworse.