Warren,

Might you have a bigger tank than you expect? Mine is 160, and I've filled up at various full levels, and I'm pretty sure that I get about 40 gallons for each indicated 1/4 tank.

I've taken mine down only to 1/4 tank (hearing the same as you), and at that point it took about 120 gallons. Bad thing on an 8V vs Series 60, that comes at about 600 miles, rather than 800 miles!