[Driveshaft Shop]

Originally Posted by CumminsFan

Main fuel feed line to the engine is typically 1/2" id tube, return line is typically 3/8" id. The lift pump is typically relies on vacuum to pull fuel forward to the engine. The lift pump typically has a return pressure is a couple of PSI. Assuming a single 3/8" return line split by a tee into equal length 3/8" tank return line, if equalization occurs, it is going to take many, many hours of operation to see any significant difference. You are not likely to see any significant equalization in an hour or less of operation using the OEM design. You may be able to alter these dynamics and line pressures by using an aftermarket FASS or Air Dog fuel filter/pump system.

The fuel return on a multi tank system is designed on equal pressure (i.e. equal pressure loss) to the tanks to more or less split the returning fuel volume evenly between both tanks at the tee. This design does not lend itself to equalization. However in the real world, the return line pressures are never quite equal. Return lines with reduced cross section, tight bends, different flow fittings, etc. cause different flows. This leads to the returning fuel flow tending to be higher to the tank that has lower return line pressure loss. Generally this imbalance is small and is not a problem.

To truly get equalization between the two tanks, you are going to need to install a large diameter connection between the bottoms of each tank. Manufacturers moved away from this bottom of the tank connection due to fuel spills caused during accidents or road debris penetrating the equalization line. The operator doesn't need to manage fuel levels between tanks with this approach. Alternatively, you could install a fuel pump to move fuel between the two tanks but the operator would have to be on top of fuel levels in the tanks to prevent overfilling a tank. Either approach sounds like a problem waiting to happen for different reasons.

If one tank is run dry and the tank pick up is pulling air, an engine non-run condition will most likely occur. Fuel flow to the engine will stop (due to the air being introduced into the fuel system by the empty tank and the loss of vacuum) even though the other side tank may have plenty of fuel. To return engine operation, the empty tank will require additional fuel, and the fuel system will have to be purged of air.

Hope this helps

well now im confused, i did the test to see what happened and it seem to have worked out, i drove on the Hwy for a bit but not that long.