My father in law used to have a Taurus of that generation. He said he would get 38 mpg on the highway. Not sure what engine or final drive he had, but he had stock dual exhaust and he thinks that was the reason for his good mpg (but he knows more about his Fairlane than anything 1980 or newer.
Later on he bought a newer generation Taurus. He said he only gets low-mid 20s with it and says it is because of no dual exhaust
. Anyway I drove it once for about 10 miles, and it certainly is not geared for mpg. It has a lot of low end torque, but after 35 mph the rpms just keep going up.