my engine temp consistently is just above the warm line, could this be a bad thermostat? it runs great but gets p---s poor mpg 10 to 12. what do you think of my theory that the engine is never warmed up enough to run efficiently.

4.6 scab/longbed/97 w 144k miles

 

It sounds like the thermostat may be stuck open. If this were a faulty sensor, the MIL should be ON.

An always open thermostat would keep the engine too cool. The sensors would read this and keep the fuel trim rich constantly in an effort to bring the engine up to normal operating temp.