Uneven fuel level in tanks.

[TRUCK365]

2020 Freightliner Cascadia
Truck will consume fuel from one tank only and wont even out with second tank. In other words. If you fill one tank all the way and keep the second tank at 50% the levels will not balance out like it used to. I took it to the Freightliner dealer and they replaced the sending unit along with both vents and vent hoses. One week and $1400 later the problem persist. Anyone had this happen before? Ideas? Thoughts?

Thank you all in advance.

[Rawze]

trash in the return line splitter valve above the tranny?

Maybe disconnect the fuel lines at the tank and at the fuel-water separator and blast some air thru them from both directions to ensure they are cleared out?

Has this truck always done this? or did it just start?.. maybe you got some trash in one tank and its clogging the pick-up tube on the one side?

Maybe the vent tube got a wasp (dirt dobber) nest in the end of it?--- This time of year that is common.

also might want to check for a kink in the line?

[DVT873]

I don't know about Freightliner but on most NAV units there is not an equalizer line across the bottom of the tanks. Instead there is an electric fuel pump that moves fuel from one tank to the other. Draw tank is usually but not always on the pass. side. Body computer compares the levels and moves fuel as needed. Engine has to be running for transfer to happen. There is an inlet screen in the pump that occasionally plugs up. Pretty reliable system now. Very very early they tried using a 5 wire pump that read the sending units directly. Lots of problems. That was gone by mid 2000's.
Before that it was dual draw dual return. Those had some problems. All the lines had to be on the same level. No kinks or dips. You would get to much fuel returning to one tank.
Be best to figure out what you have.
If there is a sending unit in each tank there is likely a pump somewhere. The NAV dual draw dual return only had one sender.

[Aussie Steve]

My C120 used to have taps on the manifold above the gearbox. A long time ago I had trouble with it only drawing from one tank and loosing its prime overnight. The taps had screens on the inlet from memory. I priced new taps from Freightliner and decided to remove the taps all together as they were worn on the tap shaft and sucking small amounts of air. It took me a while to troubleshoot the fault. So I removed the taps and plumbed everything together, it now draws and returns to all four tanks evenly. For those who will say what if...... and you need to isolate a tank for some reason. Well in eight years since this mod the need has not arisen yet but in the toolbox is enough JIC plugs and caps to isolate three tanks, this truck spends 95 percent of its time off road in pretty ordinary conditions.
The taps would be a good starting point, Oh and it's Cat powered but I don't think that would really make a difference.

[TRUCK365]

Hi guys, I am back after a reassessment of the situation based on everyone's input. Turns out that instead of a splitter valve, this 2020 Cascadia has a simple T (either that, or I did not find the splitter valve). We took apart the return line and T going to both tanks. Nothing came out. No obstructions. We took out the vents and vent tubes, blew some air in them also. Nothing came out. Put everything back together and sent it out with the driver for a short test run. Going on three days without a problem so far. Driver is able to fuel up and tanks equalize just fine. It seems that whatever we messed with did the trick. A huge thank you to everyone that contributed.

[SquareOne]

Thanks for the follow up...not long ago I had a similar issue with a Cascadia. It was a bee nest (as odd as it seems) inside the driver tank vent. I make it a habit to check these regularly, but this nest was about a 6-8in into the vent.

Long story short, it caused all the fuel to be pulled from the pass side tank (and shut the truck down of coarse). Simple fix, but a large headache at 12-1a on a Sunday night lol.