Striking a balance

Most all systems include a pickup tube which pulls fuel from near the bottom of the tank, using a ½” to ¾” line connected through the top or side of the tank (location dependent on the manufacturer). The system can include either a single tank or multiple tanks with draw and return fuel piped to the engine. With multiple tanks the capacity can differ if the diameters are the same and they are located at the same height on the frame rails.

Equal length suction (draw) and return line lengths must be employed to create a balance. Even if the tanks are staggered one behind the other, make sure the suction (most important) and return lines are the same length before connecting to the T-fitting. The lines absolutely must be the same size, tube material, and routed exactly the same. Either both over, through or under the frame rails.

If everything is plumbed correctly, and one tank has more fuel than the other, the system will automatically level, even if the engine is not running. Certainly, it will level much faster with the engine running, because the fullest tank provides the engine with most of the fuel supply until the tanks are level, when they pull fuel evenly.

If the chassis is parked on a hill with the passenger side lower than the driver side, then fuel will automatically move to the right side, lower tank. Remember, the fluid is always seeking to be level. If you are relying on fuel level gauges for accuracy that is probably not a good idea. I would not anticipate dual fuel gauges to show exact levels.

If you are truly experiencing an imbalance do not assume the line lengths are equal… measure them. Also check the lines for a kink or a rubber flapper, which could have been created during the manufacturing process, depending on material. Next look at the vent line if the tank has one, if not, the vent could be in the cap. It’s imperative the tanks are vented to atmosphere. If there is a restriction, this too will cause an imbalance. If you hear a hissing (either suction or pressure) sound when the cap is removed, the vent is not working properly. Insects have been known to build a nest covering the end of the vent line.

The issue that most everyone overlooks is contamination inside the tank. Ordering an anti-siphon device and/or locking fuel cap is advised to help keep garbage out. Plastic caps or the seal off diesel fuel conditioner/additive jugs are common culprits. We’ve also heard of shop rags, newspaper, clear cigarette cellophane wrappers, and how about a tuna fish can... (are there any disgruntled people hanging around?) Basically, anything can plus the fuel suction line. As soon as the engine stops, whatever is plugging the pickup tube falls off, just to have it occur again at a later date.

When suction ceases or is impeded, it has no effect on the return, the engine returns fuel to the tanks at the same rate regardless of fuel level. Therefore, one tank is over full while the other is empty. In this condition, the culprit is debris in the full tank. Drain and clean the full tank. And know that contamination could occur in both. If all has been investigated and still no resolution, a crossover line might be the last resort. Crossover lines are still legal, contrary to what folks say. It is advised to protect the line from road debris contact, and use double-check valves at each end of the line.