Do you live somewhere where it's cold? If you run the defrosters you are also using more gas cause the front defroster runs off the compressor. My 05's gas mileage computer is pretty much dead on when I calculate the mileage manually. My 03 is way off - don't even bother with the cars computer - just do it manually.

 

My 02 Computer is off, says better mileage than actual, it also says lower gas used than actual which is really the problem. All I use that display for is direction and temperature, all the rest is a waste.

 

I wonder if that's the case with all the early Montes.

 

I'd be pretty happy with 14. I'd be happy with 6 doing what you're doing.
I hope you're driving this car more than that. It take's about 10 minutes of driving to get the moisture out of the exhaust, get the tranny warmed, etc. You're killin' your car. Get it out and DRIVE it at LEAST every few days.
Forget the 10 minute warm ups if you're concerned about mileage.

 

if its not that far id walk to work lol

 

I wouldn't bothering letting it warm for 10 minutes..

I live in buffalo, where the high for the last month has been like freakin 9 degrees, and I just let it warm up for 2-5 minutes at the very most. Im averaging 21.4 mpg now, according to the computer..I must have the only computer that's accurate, I've done the math two other times to compare it, and it was only off by .3 at the most

 

I have 3 montes in the past 7yrs. My first was an 2003 SS non supercharged which was excellent on gas. Then I had a 2006 LT1 with the 3.5 which was even better on gas prob around 33 on long trips. Now my 06 SS with the 5.3 and the MPG is HORRIBLE !!!mostly if not all highway only 19.4 avg mpg...wtf

 

That's V8 power for you, lol!

 

Got an 08 Impala SS, mostly highway @ 80mph I'm getting 21.5, even the 95 Z28 got 20.1. Both better then the Sierra with the 5.3, I was getting 17.6. The Monte will get me around 27.

 

you bought a v8, you shoulda expected it, if you run it for more than a minute, it uses more gas than it usually would starting the car up over