I have a 2000 Monte SS with 141k miles,

My problem is I get around 17 mpg city 20 hwy. I know this has to be a little low

I keep up with my oil changes, sometimes I actually do them early, and use high mileage oil high grade oil, replace my filters, just had gaskets replaced.
I do have 2 12"s in the trunk and 20" rims but even before them my gas mileage was pretty low.

The transmission is also newly rebuilt about 1000 miles ago.
The engine runs strong and idles smooth.
I really cant see any obvious problems as to why this would happen.

It does have a slight wine when taking off that may be an air leak but from what I hear this noise is notorious in monte carlos.

Any input is appreciated, Thanks, J.

 

A lot of your answers may be answered >> in this thread<<

 

Get a new air Filter, Try some fuel additives, I used Prestone All fuel and carb cleaner, as well try some engine oil additives, Ive also used zmax. after a week or so I increased my mpg overall by about 2 to 3 mpg as well as some lost speed.

 

There's also the possibility of all of your sensors being old and wearing out. Your engine could have build up inside of it, the car could be running rich.