I just bought a 2008 Impala LTZ about 3 weeks ago. Went out of town this weekend, only got 23 MPG. I was expecting 28-30. Is this normal or do I need to get it chacked out?

 

I would try putting higher octane gas in and see it that helps. The only time my 01 empala got less than 20 mpg on the highway was when my cadalidic converter went out on me between North Dakota and Montana. Had to drive 500 miles at 3000 RPS and only going 50 mph. It was rough.

 

You should never use a higher octane gas than what the manual reccomends. Im not sure what is recommended for the 3.9L, but using a higher octane than needed would actually be detrimental to gas mileage.

23 Is not as terrible as you think. The 3.9 creates a good amount of horses, and it takes gas to make horse power. Also, im not sure how much of your driving was city and how much was highway. If it were all highway, I would expect abt 26 with the LTZ, but if you throw some city in there, 24 or so would be typical.

I average 19.5 in my SS with half hwy/city. But I am also VERY hard on the gas pedal

 

Thanks for the help.
The mileage was all highway miles. I didn't calculate the MPG, it was what the trip computer reading said.
My wife didn't write down the mileage so I can't calculate it the right way. I know it took 15 gals to fill it up when she got back, and it is about 360 miles between towns. That calculates to 24 MPG. I was expecting better than that.
I guess I need to check how accurate the trip computer is. The next time one of us takes a road trip, I'll check it again.
I was just wondering if I needed to have it checked by a shop to see if something is wrong.

 

It is unlikely that you have an issue... What is the recommended octane for the 3.9L vs. what you were using? Did you find yourself into the throttle at all? Once you tap into your engines power reserves, your gas mileage likely drops of by about 4-6 mpg.

But lets put this in retrospect.... My 4 Cyl Camry got 25 MPG on a GOOD DAY. You have a LARGE 6 Cyl and you are getting 24 .... Sounds great to me.

I think we are all so jaded by hybrids and 30+ MPG cars that we have lost sight of what is actually GOOD gas mileage. Like I said, it takes fuel to make horse power, and having driven the LTZ I can say for certain that it has some impressive output. And that extra 3 MPG wont add up to a hill of beans by the time you are said and done.

 

On the road (highway) my '02 gets over 30 with a 3.8. Either you were going uphill, driving over 90 or you need something checked out. Terrible mileage indeed.

 

My 06 Impala went to Gallup and back today and averaged 32.5 mpg. Get to know your on-board computer and zero-out the A or B trip odometer when starting off. I beg to differ with other members about the octane level of your fuel. If its a FlexFuel, it should run good on most anything. Another thing, Impala LTZ=3.9=fun to drive and lots of zip. Watch you lead lined shoes (right side) especially.

 

Thanks for the feedback.

I think it should get better than it is getting.
I'm hoping the computer is wrong. Will calculate the mileage the next time I go out of town.

 

From what I have learned, there is apparently a larger fuel mileage difference between the 3.5 and 3.9 than the EPA ratings indicate. My 08 LT with a 3.5 has almost 52,000 miles on it. My highway mileage on 70 MPH interstates averages between 31 and 33 MPG for round trips. I have gotten as low as 30 and as high as 34.

 

While the timing on the new impalas automatically adjusts to differing levels of fuel combustion, an engine will only deliver MAXIMUM MPG's when using the reccommended octane. My SS runs fine on anything, but using lower than 91 octane results in a loss of gas mileage. The same thing goes with a 6 cyl. It all has to do with the compression ratio... the pistons need to be able to complete a full stroke prior to fuel detonation.