99 4x4 pickup with 171,000 miles. My mileage stays the same but my tank takes less and less gas. With a 13.5g tank at half full I should take about 6 or 7 gallons (I know the guage is an approximation) but I can only put it 3 or 4. This happens alot. I used to get 170 miles to a half tank and now I get about 100. My milage stays consistent. What could have 'filled' my tank?

Most likely, nothing has "filled it". The fuel gauge operates by varying the resistance in the groung circuit. As the truck got older the float unit became more & more corroded, increasing the resistance in the ground circuit. As a quick & dirty test, disconnect the fuel gauge wire at the tank. The gauge should go past full. Then ground the wire, the gauge should bottom out. If these things both happen, the gauge & all the circuit are all good. That leaves only the sending unit to be the culprit.











Craig