taurus gas problems?

my mom just got me a used 95 taurus, with like 52K miles on it. this is still my first tank, but i've only driven 90 miles and it says my tank is half empty already! is it because it's like 0 degrees here or something?
maybe cause i'm running the heat? i'd like to know what the hell is up with this thing...

I've a similar problem with my 2000 SEs Duratec. Allegedly an 18 gallon tank yet from just above the "E" on the gauge, filling really slow,it will only take 13.5 gallons, which menas i only get around 300 miles per tanl. I think this is a Ford trait.