I am a new owner of a used 2001 210 bowrider. The gas tank is (apparently) filled to the brim but the fuel gauge reads about 1/3 of a tank. If I run it an hour or so it is down near empty. Is there any way the tank can be apparently full but really be near empty? Or is the sending unit, or tank float or console gauge faulty? How do I go about trouble-shooting this problem? What is the approximate fuel consumption per hour on this boat (at cruising speed / and at slow running)? Thanks very much for your advice.