Another thing to watch out for when trying to increase fuel economy in the current Sentra is the A/C. Whenever you dial-up defrost or defrost+floor, and the fan speed is above "0", the a/c turns on. On pure defrost, the a/c light won't come up, but it's still on (did some RTFM on that). Push the a/c button to turn it off on defrost+floor, and the a/c will still be on even though the light turns off.
Solution: unless you don't have defog weather, use flow-thru (fan off) if you want the airflow from the defroster outlet.
Still, some of my best scores came from summer runs with a/c on.
Other Sentra attribute: on top of the roomy interior, the trunk offers a midsize-class 14 cu.ft.