Fuel imbalance from Aux tanks, then Mains

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  • #83703

    We have been experiencing fuel problems with our 1980 C340 Ram VI. When on long trips, I have noticed that the left side Aux tank will indicate and run dry in about 40 min or so and the right tank will still show fuel and run for another 30 min or so. When we switch back to the main tanks, the left side is at roughly 10 gallons higher that the right. Fuel flow on the Shadin is equal on both engines and set to the specific Ram setting. I have noticed that the right side fuel selector is somewhat sloppy and missing the detent like the left side. Is it possible that the right side selector is caught between both the aux and the main tank and using fuel from both tanks? Thanks

    sblue

    #95625

    I think you diagnosed your problem. I have not seen how the valve works but know the plumbing, I would come to your same conclusion and your Shadin is confirming the fuel totals.

    #95626

    My 414 did the same thing. The fuel pump on your left side pumps faster than the right side. The fuel that isn’t used by the engine is pumped back to the main tank. I believe that there are adjustments on the pump, but it may be that your right pump is getting weak. 40 min is about right for a strong pump.

    #95627

    BTW, your Shadin just shows the fuel flow used by the engine, not the flow out of the tank.

    #95628

    Did not think of that, flow and pressure do correlate. Good point, and easy enough to verify to rule out plumbing.

    #95629

    A couple comments:
    1. 40 to 50 minutes of run-time on 31.5 gallon aux fuel seems to be a good reference point. 70 minutes seems too long.
    2. When cycling through the Off-Main-Aux-Cross feed settings there should be a noticeable detent, not a mushy feeling. You might want to pull the valve access cover on the top of the wing and inspect the valve or have your A&P pull the cable and check to be sure the valve is working correctly from a detent perspective.
    3. If after cruising on mains then aux to exhaustion then back to mains, the fuel quantity should be equal in each main tank assuming roughly equal fuel flow to each engine. That is regardless of the aux transfer time. If you end up with significantly more (e.g. the 60# differential you cited) then the valve is likely leaking through the cross feed outlet.

    Have you noticed any cross-feed after fueling?

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