I am driving a 08 Impala LTZ with the 3.9 engine in it and am only getting 22 mpg on the Interstate traveling 75mph. I just traded a 06 LTZ with the 3.9 and got 27 mpg at the same speed. What is the average mpg that people are seeing with 08 3.9 liter engine?

 

are you calculating this by hand or using the DIC?

 

I zero the trip counter every time I fill and do the math on the next fill. If I drive 55 it gets about 27, my 06 got 33 at this speed. Dealership is telling me that 22 is the normal report for this year and make of Impala, just seems unacceptable to me.

 

T.S.
Yup my 06 seems to get better than some of the 07 and 08's that I've rented. Did notice that my 06 tends to sorta bog-down when shifting into OD that the newer Impalas don't seem to do. Don't suppose they have changed the tranny gear ratios to get a little more response at lower and mid range speedsin lieu of mileage? Bet they did and this probably accounts for your decrease in mileage. I've also noticed fuel quality and have started using Lucas fuel treatment which also seems to help. I don't recommend anything to anyone, so buy and use at your whim.

 

Also, my Impala and all the rental units were 3.5's not 3.7 liters

 

Has anyone tried anything else aftermarket with any success, our company pickups are getting 17 to 19 mpg, it wouldn't cost that much more per year to drive this versus the Impala.

 

Have you checked to make sure you are running factory size tires? A little bit bigger tire would rack up less miles on the trip meter throwing off your fuel mileage.

I put new tires on my bro-in-law's pickup a few months ago, they were a hair bigger, but it made about 5 mpg difference if you calculated it the way you did. But I told him that the bigger tires would show less miles on the trip meter so it actually comes out almost the same.

I personally use GPS to track my miles as it is a lot more accurate.

Just a thought, since I own a tire shop I run into this situation almost every day talking to customers about tire/wheel sizes...

 

Yeah! What she said..............^

 

Car has factory rubber on it yet. Everything is as the sticker says, just not the mpg rating.

 

how many miles on the 'new' car, it will improve as you put more milage on it, vehicles get their WORST milage when new generally. You said you just traded your other one in. give it 10,000 miles to break in.