I own a 2006 Five Hundred Sel with 87,000 miles. It's in remarkable condition for its age minus one little issue. I am getting terrible gas mileage on the car. I am only getting about 15 miles to the gallon. I don't speed in it, Oil is always changed every six months even if not needed. It's not the all-wheel-drive version. Has the normal 6-speed transmission. I have known this car its whole life, It was inherited but it was always garaged and taken care of through the Ford Dealership. That being said I do not think it ever had a tune-up sense it was bought. Could that be playing a factor, or could it possibly be something totally different? The Tires are only 3 years old and alignment was done last year.

 

87K is time to replace the plugs,air, gas filters and a transmission maintenance. It's highly doubtful that this will bring mileage up much. I would then connect a scan tool capable of displaying live data to see what your long term fuel trims are at. That will give a good idea how well the engine is running. A reading of zero is perfect but unlikely. You want a swing of +/- 5. If you are in that range, not much else will bring gas mileage up. Then start looking at things like dragging brakes, under inflated tire and poor driving habits.If you are doing very short trips, 15mpg would not be that unusual.

 

I have a 2006 Limited with the all wheel drive. My car has always been meticulously maintained as well and except for the fact that the style is now outdated you would swear it was only a year or two old. The car has 146,000 miles on it. Even with this V6 I tend to get anywhere from 17 as a low and up to 30 to 35 miles per gallon. Around city is where I usually get to 17 to 19 miles per gallon. On a good stretch of highway at higher altitudes for whatever reason which I have no idea, I get really good mileage. Again this being with a V6. A few years back I had a Ford fusion with a four-cylinder in it and on more than one occasion I was able to get 50 miles per gallon out of that thing. And no that’s not downhill. Same stretch of Road at about 6000 feet. I don’t know what would cause yours to get such a low miles per gallon. As well as I have no idea why are you a high altitude gives a car better mileage. It sounds like yours has been very well-maintained as well.

 

I do live at the 3600-foot level in the desert, It's rare when I do go on longer trips maybe I need to start doing that. But then again i am not totally mechanically inclined
. I just want the car to last as long as possible.

 

That MPG is normal, for the heavy Five Hundred. The Pinto would get better mpg, keeping it in the Ford Family,

 

A little side note, it is amazing how many folks think regular oil changes are all one needs to have done to be considered good regular maintenance.

That is only part of the maintenance required and the best procedures to follow are in the owner's manual.