Gas tank question HELP!!!

[painterljp]

Have a 72 gmc longhorn, well Sierra Grande. Has three tanks. Has the selector on dash for am assuming just the gauge reading. The selector on floor next to seat with no markings. The valve under truck has 4 ports. One from each tank then one going out. How is this gonna work with the return line on the pump? The fuel pump has 3 ports. One from tank one to carb and one to ?? Had a 2 line on it when we got it. Have just rebuilt the engine and don't really want to mess with other two tanks for now. They need pulled and cleaned, but really want to start New engine and just run it off tank behind seat for now. Guessing other is return? Sending unit have to replace in tank behind seat. It is 2 line. A friend here has a new one gonna go get today. But unsure if return is going to cause fuel to be returned to what tank? It is a four valve switch under truck. Any info would be appreciated. Thanks in advance.

And is this factory, Aftermarket?

[painterljp]

Nobody's two cents?

[B. W.]

If you are just running the main tank then plumb the two lines as usual to that tank. Bypass the selector valve.

When you do get the saddles working you will need to switch to a pump with no return port.

(my DD has an aux. tank with a return line on the pump going to the main tank. When it is running on the aux. tank it fills up the main tank! That way when I bought it ten years ago, I'll fix it one day)

[painterljp]

It does have a return line on the frame and on the sending unit. Thats why we bought a 3 line pump also. But I agree that if return line is hooked up whatever fuel it returns is only going to go into main tank. Filling it back up I guess. Only remedy is to run a two line pump?
That was the way they did it back then? Doesn't make any sense. What were gonna do today I guess is disconnect the fuel line on passenger side under the truck where all these lines are hooked up and put an inline filter and 3/8 line and Connect only main tank. That way we aren't disturbing rest of fuel system. Until we get around to doing it. Behind seat tank holds what 16 gallons? Shouldn't go to far with a 402.

How are you gonna fix that?. Let me know maybe you can fix ours too!! Ha ha!!!!

[Rufas]

Originally Posted by painterljp

It does have a return line on the frame and on the sending unit. Thats why we bought a 3 line pump also. But I agree that if return line is hooked up whatever fuel it returns is only going to go into main tank. Filling it back up I guess. Only remedy is to run a two line pump?
That was the way they did it back then? Doesn't make any sense. What were gonna do today I guess is disconnect the fuel line on passenger side under the truck where all these lines are hooked up and put an inline filter and 3/8 line and Connect only main tank. That way we aren't disturbing rest of fuel system. Until we get around to doing it. Behind seat tank holds what 16 gallons? Shouldn't go to far with a 402.

Should be a 20 gallon tank.

[B. W.]

Oh, by fix I mean replace the three line pump with a two line! I guess I'm waiting on the pump to die.

[Rufas]

Originally Posted by painterljp

Have a 72 gmc longhorn, well Sierra Grande. Has three tanks. Has the selector on dash for am assuming just the gauge reading. The selector on floor next to seat with no markings. The valve under truck has 4 ports. One from each tank then one going out. How is this gonna work with the return line on the pump? The fuel pump has 3 ports. One from tank one to carb and one to ?? Had a 2 line on it when we got it. Have just rebuilt the engine and don't really want to mess with other two tanks for now. They need pulled and cleaned, but really want to start New engine and just run it off tank behind seat for now. Guessing other is return? Sending unit have to replace in tank behind seat. It is 2 line. A friend here has a new one gonna go get today. But unsure if return is going to cause fuel to be returned to what tank? It is a four valve switch under truck. Any info would be appreciated. Thanks in advance.

And is this factory, Aftermarket?

OK I'm not familiar with a 72, but did it come from the factory with a return line to the gas tank in the cab? My 70 GMC did not. I looked for pumps for your 72 and you can use either a pump with a return line or one without a return line.

From the photo of fuel valve you provided, there is no provision for a return line associated with that valve. Check the tank in the cab to see if there is a return line going to it. I suspect there isn't.

If no return line to the cab tank, just get a fuel pump without a return.

Standard pump without return line.


Pump with return


Either pump is less than $20.