I've got an 1988 F150 302 EFI SuperCab. It's an automatic with overdrive. It's getting poor gas mileage (12-13 MPG) and I believe I've narrowed it down to the engine not warming up to proper temperature. It's got a new heater core, thermostat (190 degree) and antifreeze. The temperature gauge on the dash rarely reads over 1/4. I'm lucky to get to the "N" in normal while driving. I believe the computer is reading this as a cold engine and leaving the air to fuel ratio higher than what it should be. Is there a thermostat that allows an engine to warm up beyond 190?

 

190 is the proper thermostat. Sometimes people swap out the stock temp for cooler-running ones, I've never heard of using hotter ones. Sure, they're available, but that would be a cover-up rather than a fix.

On my old truck the gauge only ever rose to about "O" in normal, though that was the I6.

I get about 13mpg regularly...unless you used to be getting more and it's suddenly dropped, I wouldn't consider that odd.

How's your heat? Do you get hot air once the motor is warmed up, or is it just lukewarm or tepid?

The stock temp gauge is like all Ford gauges, crap. Don't rely on it. You can buy an old-school mechanical temp gauge from the auto store for about $20 and it's really easy to install on the V8's, it screws in right in place of the stock temp sender(right next to the distributor). Then you'll see if you're really running too cold and have a functional gauge for the future. The gauge on my truck rises to just over 190, and then slowly bounces between about 190 and 170 during normal driving.

 

The heat is okay, not too hot, though. I can try the temperature gauge and see what it says. Thanks for the input.