Super C Saddle Fuel Tank Problem

[blueflame]

I have a Super C on a Freightliner truck (not motorhome) chassis. The truck has saddle tanks (one on each side below the driver and passenger doors). Until today I've not noticed any difference between the two tanks. Today as I arrived at my destination the engine seemed to be idling rough. Then I had problems starting it (had to crank much longer than usual).

My first suspicion was fuel, which should not have been low as I had over 20 gallons shown as remaining (I use Silverleaf VMSPc). I checked to make sure the filters were open and I didn't have any water in the settling bowl. All checked out OK.

Then I looked into the tanks themselves. Using a flashlight I could see into the tanks, and using a dipstick I could measure the fuel depth. What I found surprised me. The driver tank was almost empty, to the point the open end of the intake line was becoming exposed to the air (thus the rough idle and poor starting, it was sucking air). The passenger tank had over 8 inches of fuel in it. I had been told the tanks were connected and the fuel levels would remain the same, and I always fill then both to the top.

So, my questions. Was I misinformed? Are saddle tanks really independent and I should not expect them to remain at a consistent level? What would cause the fuel to be used at a different rate from the two tanks when I have both the tank valves fully open? Any ideas on how I can account for this difference so I know before I run into a problem, since the fuel gauge and VMSPc only report a total value remaining, not a tank specific value? Any other solutions/ideas?

Thanks for any help, input, or ideas.

[dickandlois]

BlueFlame,

Do you know what tank supplies or is supposed to supply fuel to the Generator?

The generator pick up is set a little higher in the tanks so you do not run out of fuel for the engine. Is it possible that they might have been reversed in some manner?

Got to start somewhere and just maybe the pickup is in the one with the fuel and they got reversed ? Engine pick up connected to the generator is feeding the engine and not the generator.

Try to start the genset - if it runs fine then that would be where I would start looking for the plumbing error.

Rich.

[rpelatt]

Most saddle tanks have built in equalizers, but generally only one return line for unused fuel. Your return line probably is in the tank that measured the fullest. Try measuring them again after shutting the engine down and waiting a while. It should level out.

Bob

[bm02tj]

On my FL80 I can fill one saddle and it will equalize with the other one

so check for a pinched or plugged balance tube

[huffypuff]

Most dual saddle tanks have a hose at the bottom of both tanks that runs parallel to each other. One will be a feed tank and other secondary. You have to make sure that the line underneath runs flat between tank or the secondary tank level when you reach a certain level.will be different. Be sure the line don't loop upwards. The line could of been run on a piece of protected metal that got bent upwards from road debris.

Second edit, I wrote this before my coffee kicked in.

[dickandlois]

Good Point regarding the equalizer hose on the dual saddle, But it would be prudent to know what side of the coach they draw fuel for the Generator.

Got to believe that they would install the generator pick up line higher then the engine pickup line, so you would not drain the saddles and not be able to make a fuel run.

Rich.

[obedb]

The low hanging crossover line went away sometime ago. Probably because of fuel spills when running over something such as recap rubber lying on the road. My 2001 Western Star had the "new and improved version" that supposedly equalizes from the top. It was common when running down the road to see different levels when you stopped. The transfer pump draws from only one tank. Check the fuel line to the engine from one tank or the other and you will know which tank it draws from. Also suggest not running your rig quite so low until you figure out the cause. If you decide to pump only a small amount of fuel into your rig make sure you put it into the tank that the engine draws from.

[jleamont]

Double check both tank vents, the newer vent designs are creating a problem in the industry most have a small filter on them and they clog causing the main tank to empty, while the other remains full unable to cross flow.
I just had a new Volvo tractor do this, same complaint from the driver as you wrote above, the engine could only get enough fuel to run poorly, mostly drafting air-- under a heavier load it would stall intermittently.