I have a 1997 Ford Expedition, 212,000 miles, it still runs great. I’m averaging a little over 14 MPG. How does that sound for gas mileage with that many miles on the engine?
Fuel economy generally remains the same for the life of the vehicle unless there is some type of failure. I have three vehicles with approximately 200,000 mile on them and they all get the same gas mileage over the years.
My 1996 Dodge Stratus with 235,000 miles still gets only 29 MPG on the highway. My Dodge Ram gets similar fuel economy as your SUV, 12 MPG city/17 MPG highway, fortunately I only need the truck for about 1,000 miles each year, I wouldn’t drive a gas hog like that as a daily driver.
You don’t say whether you have the 4.6L or 5.4L engine, or RWD/4WD. Still, you are about at the EPA average for a 1997 Expedition either way. You are doing fine.