Originally Posted by Mhisle
Backtrack - we left the walk thru thinking the fuel gauge was broken - we agreed to take it to a Ford dealership when we got back. Gauge showed 1/4 tank - service department assured me tanks were full. After 100 miles gauge was going down. I was able to fill the rear tank full - AFTER 30 minutes of very slowly filling. Gauge showed full when I was finished. The Tech looked at this issue as well and said it was a design flaw in the lines...fun times...but I could live with that.
I have an SV34 and I can educate you on the fuel tank operation and filling.
First, when both tanks are full the smaller front tank is used first. When it drops to 3/4, the computer switches to the larger rear tank. When the rear tank gets down to about 1/4 full, the computer switches back to the front tank. You can see this on the dash by switching the display to show the gauges for both tanks at the same time.
Next, you can't use the high-flow pumps at trucks stops..... unless you limit the flow with the trigger. Those pump nozzles have a large opening (about 3 times larger than an auto diesel pump nozzle). Even though they fit into the filler openings on the F-550, they are designed to fill tractor trailer fuel tanks with a wide mouth opening and large tanks on each side of the tractor. It fills those large tanks very quickly because there is no "plumbing." The fuel dumps directly into the tanks.
Our coaches have plumbing from the tank filler openings to the physical fuel tank. There are one or two 90 degree bends in that plumbing. When using the high-flow pumps the diesel will start to backup and foam because of the restrictions in the plumbing and this causes the pump to kick off prematurely. If you use an auto diesel pump, you will not have any issues filling either of the tanks.
I know it can be a hassle to find auto diesel pumps with easy access in and out when towing but I have not had any issues in the last 10 months. Many gas stations put auto diesel pumps on the outside of their pump islands so larger trucks. I will use truck stops if all else fails and then limit the flow with the trigger but I use auto diesel pumps 90% of the time.