Well I took the gas tank out of my 51, 3600 this weekend. The truck had been setting in a field for years before I got it. I drained the most foul smelling gas out of it you could imagine, five gallons worth. Now one end of the tank, the end opposite of the filler, weights about 5 to 10 pounds more than the filler end. Any guesses as to what is in there weighing it down? It won't roll or shift around when I tilt the tank. Guesses?!!
