Hi,
I know someone who ran his Bounder out of fuel while on the interstate, and then added 10 gallons. It was not enough to prime the fuel pump, as the intake is in the center of his tank, and sitting on the edge of the roadway, it would not reach from the side of the tank to the center. He ended up needing a tow truck to get the RV level, before it would start again.
If you do decide to run it empty, then I would suggest having about 10 gallons of gas on hand, in case you need all of it. Your tank is a bit smaller than the 75 gallon tanks on the class A chassis. They actually can carry up to about 100 gallons of fuel and air.
Chances are that you have the standard 55 gallon tank for the E-450. Optional on the E-450 is the 40 gallon tank, while the E-350 has a standard 40 gallon and DRW E-350's can optionally get the 55 gallon tank.
IT is best to always cover the fuel pump inside the tank with fuel, it will run much cooler, and last much longer. Not wanting to remove the tank, then replace the pump from the top of that tank, I would not be wanting to run it dry very often. Filling every 40 gallons will give you about 280 - 320 range with 7 MPG or 8 MPG respectively.
My buddy can fill his tank full if the RV is leaning towards the passenger side much better than when it is level. He has put in up to about 39 gallons to the rear 33 gallon tank, once he installed a front tank, and can run the back one empty. Then he can put 8 gallons into the front 16 gallon tank, and be on his way. His range used to be about 20 - 25 gallons before needing to find a gas station, before installing the front tank.
I put in the front tank, removed from another Ford van. The E-350 dually 1986 chassis had the same holes in it for that front tank as any other E-350. By going to a junkyard, we found a fuel filler from a E-450 based shuttle bus, and removed that, took the fuel filler home and figured out a place to install it on the driver side, away from the water heater and refrigerator. Then ran 2" muffler tubing with gas fuel hose connecting it all together. We used factory 90's made from muffler tubing, with short pieces of fuel hose connecting the long straight pieces with the bending pieces. For a vent line, we used some 1/2" fuel hose for the whole length, going uphill all the way from the tank to the filler vent connection. The new front tank sits between the driveshaft and chassis, on the drivers side.
You might have a vent problem, that is not letting all the vapors out of the tank, before fuel is backing up in the fill line, causing the filler to shut off before the tank is full. If you can trickle in another 3-5 gallons of fuel to the tank, then you might find you can improve the filler neck problem, and get that much more fuel in each fill up.
But if you can only trickle in about 1 gallon, then your tank is "Full" and you are only getting out a marginal amount of vapor, and actually overfilling the tank a little bit. Heat from the road and gasoline expansion can cause the tank to overfill, even though you might be driving 60 MPH and using 5-6 gallons per hour, you can overfill the tank for those first few minutes you are on the road as the fuel is expanding due to heating from the underground storage temperature of around 55F to the tank temperature of around 120F.
Some states, such as Oregon post on the fuel pumps that topping off is illegal. This prevents overfill of the tank, and dripping on the ground.
Good luck,
Fred.
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