Fuel return question on a Cat 3406B Motor???

JD Seller · Feb 5, 2015

I am changing the fuel tanks on a truck that has a Cat 3406B motor in it. The old style type of injection system. The old tanks had a bung that allowed the fuel to be returned directly into the top of the tank. So there was zero back pressure. With the new tanks I can't plumb the return in the top with out welding in another bung for the return line. The tanks have the fittings half way up the side with internal suction tubes that go to the very bottom of the tank. So there would be the column pressure of the fuel in the tank for the return line/fuel to push against. Will this effect how the system works??? This column pressure would not be much. The tanks are only 25 inches in diameter so the column would only be that much when the tank was completely full.

NCWayne · Feb 5, 2015

I know of several people that have 3406 engines in their trucks or equipment, and plenty of them have the return going into the tank at places other than the very top. That said, you should be fine with it going to the bottom.

VicS · Feb 5, 2015

Shouldn't be any difference in pressure even if the fuel went back in the bottom. Fuel should be the same height in the hose as the tank. I did this ran the return back in the bottom of the tank on a Detroit. Motor ran OK but, stirred the fuel quite a bit revved up. I took the elbow off and threaded it 1/8 pipe then put a pipe on the elbow that ran the fuel back to the top of the tank.

mazemeister · Feb 5, 2015

the back pressure, as you say, in the return line will be no different whether you return to the top or bottom of the tank when it is completely full. when the tank is almost empty, returning to the bottom should tend to siphon the return fuel back to the bottom so the gauge pressure of the return line, if it were measured at the injection nozzle, should theoretically be less than if it were returned to the top. diameter of the container has no effect on the pressure. so in other words, don't worry about it, it should work fine.

Owen Aaland · Feb 6, 2015

As long as the engine fuel system is above the tank there well be no pressure from the tank but instead there will be head pressure in the return line as gravity exerts a pull on the fuel in the line.

Fuel return question on a Cat 3406B Motor???

JD Seller

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NCWayne

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VicS

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mazemeister

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Owen Aaland

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