mileage
 

I know most don't care about it but I'm curious anyway. My car is pretty much stock (1991 LX coupe 5.0 ex-FHP). My mileage in the city is around 19-20 mpg. On the highway at 70 mph its the same. What gives? Here is a list of relevant stuff done to the car. Odometer: 142000. 2.73 gear. 35 psi pressure in tires - 225 60R15.

Heater Core bypassed using bypass CAPS.
spark plugs, wires, distributor, coil - all new
Super Duty T5 tranny
Smog pump removed with relevant hoses.
AIR tube capped ater smog pump removal
Mass air meter and idle air bypass valce cleaned
MSD 6
160 thermostat - temp needle stays bet 1st & 2nd mark
K&N large cone filter
new 02 sensors

Scrap the 160 thermo - wayyyy to cold for everyday driving. You're probably running too cold, therefore staying in rich mode which is contributing to your poor gas mileage.

Move up to a 180 thermo and see how it performs.

E

I get 19 around town, 26 on the road.

I believe the recommended thermostat is 192°

The Ford (Motorcraft Brand) thermostats seems to be more accurate and last longer than aftermarket types.

mileage
 

Your best bet would be to go with a 180 degree thermostat.

192* Thermostat
 

"Contrary to common belief, the computer system does not function best at 160*. Engines operating at this temperature are thermally inefficient." Mustang Performance Handbook

factory thermostat is 197degrees the stang has been shown to run best at 200 degrees.