Just measured the gas mileage on my 08 ES350 and it went 252 miles on 15 gallons, or around 16.8 mpg in mostly city driving with some freeway driving. Which is about the same as my 2004 Mercury Grand Marquis is getting. Is that normal or should I be checking into how the engine is running or something? I try to mostly take it easy on the car when I drive, but I'm not slow and do get into it a little here and there.

 

How many miles are on it?
When did a shop last check it out or do maintenance?

Have you:
Checked the engine air filter?
Checked tire pressure is correct?
Put a bottle of fuel system cleaner in the gas tank to help clean the injectors etc? Such as Techron Fuel System Cleaner, Royal Purple fuel system cleaner, Redline fuel system cleaner.

 

I need more information to give you an answer.
How many miles? Did you replace the spark plugs? Did you check for vacuum leaks? Check engine off or on?

 

The car has 120k miles on it, just bought it a few weeks ago and all I have done so far is change the oil, air filter and the rear sway bar bushings. TIre air pressure is correct. I think I'll try a bottle of Techron and see if that helps any, then go from there.