I recently purchased a 2000 Cadillac Deville DTS. According to the control panel on the car, the car has been getting an average of 11 miles per gallon. (I drive the car equally as much on the highway as I do in the city.)

I used to own a 1998 or 1999 Cadillac Deville (my mom gave me her car so I don't remember the exact year), and it got good gas mileage. I would get around 18 mpg for city driving and 24 for highway driving.

So, how a car that is similar but 1-2 years newer get virtually HALF the mileage I had before?! Is this typical for that particular year/model, or is there some problem going on that's killing my gas mileage? Oh and I use premium fuel, if that makes a difference.

Any insight would be appreciated. Thank you in advance.

 

You may have clogged fuel injectors/system. The cheapest way is to replace the fuel filter, put some LUCAS fuel system cleaner into the tank, fill tank, and drive a long way. A good distance would be 150 miles. In other words, drive 150 miles one way on the interstate, turn around, and drive 150 miles back. If your MPGs don't increase (set the display to show Instant MPGs) by the time you get home, something else is causing it.

Also, check the Idle Speed Controller, which is in the intake. If the ISC is stuck closed, it could be burning super-rich (it should open up when the car warms up). And check codes.

TS