so, i have the 36 gallon tank on my truck. The fuel light comes on at 5 gallons left, 31 used according to the trip computer (had it happen Sunday). The question I have is about how much fuel is actually usable in these. Do I have 36 gallons usable, meaning it actually holds more than 36 gallons and I can use all 36, or am I at risk of running out of gas a few gallons shy of 36? The truck told me I had 57 miles left when the light came on, but I should have had closer to 100 based on driving.

 

You’ll likely stall a wee bit shy of 36 gallons, when the fuel pump loses prime. I actually had my ‘03 parked at home on enough of an incline that the truck wouldn’t fire up, despite having what would normally be a comfy amount of fuel in the tank.

That aside, the idea of the DTE reading is to get you to a gas station before you run out of go juice.

 

^this, probably can only use about 33-34 gallons before it starts sucking air

 

If you want to really test it, put a 5 gal can of gas in the back next time the low fuel light comes on, then drive until you're out.

 

And then let the rest of us know

 

How far can you go... depends - flat road or hilly.

I filled up on Sunday and happened to pay attention to fuel used versus how much I put in. I put 84.5 litres (filled past the first fuel stoppage clunk) and gauge said 82.2 litres used. Gauge is not accurate enough to run to empty. With other vehicles in the past I have run it empty with 5 gal gas can with me to see how far I could go. A few Fords of mine in the early 2000's could go 50-80 km past "0 km to Empty" warning. It will be different with every vehicle.

 

The lowest I've ever run mine it took 33.3 gallons.
613 miles.
Mpg was a little over 18.
All highway run up I 95 from Florida to Pennsylvania.
2013 XLT Scab 4x4 5.0L with 3.55 gear.

 

I think I have used 33-34 before. Never pushed it more than that.

 

Why run so low in the first place? Are there not gas stations near? I have pretty much the same truck as you and before I “modified” it my 36 gallon tank would give me a range of over 600 miles.

 

based on what? A guess?