Ok the truck is new to me. The fuel gauge is at full at a full tank but after 100 miles it is at half a tank. I would fill up ad it will take about 7 or 8 gallons. At 1/4 tank it was like 12 gal . It would freak me out and I fill up ever 1/2 tank. Driving cross country. I see it is a 19 gallon tank. is it designed to be this way? like a 16 gallon tank with a 3 gal reserve?

 

That's about right. I've run mine down close to E and still have a reserve. Ford just doesn't want you to run dry, not a pretty picture with mechanical pumps.

 

WOW. I really need the second tank so I don't have to stop all the time.

 

You don't have one?

 

Which tank? What bed size?

 

I have a 2nd tank but I am missing the filler neck to it. its an 8' bed

 

And which tank are you actually using?

 

I'm using the front tank. they are both 19g right.

 

Long bed front tank is 19 gallons. Rear tank is 18 gallons. My general experience is that the floats/gauges are "pessimistic", that is, you usu. have more fuel than the gauge indicates. They seem to be accurate toward the top of the tank, but as it goes down, they get further off. Off by 3 gallons at the bottom end is a bit extreme; I usually seem to have about 2 gallons when it reads at/near empty. I've generally seen this with other vehicles, too. It's just a float operating a mechanical variable resistor; not exactly a high-precision instrument.

You also might not be filling the tank entirely. If you're able to fill it pretty fast, the fuel may be foaming up, causing the gizmo in the station pump to kick off. Just for grins, next time you fill up, even after "extra-clicking" it, let it settle for about a minute, and see how much more fuel you can get in.