dual tank troubleshooting

[willstruck]

I'm sure this has been addressed a million times, but I searched and didn't come up with anything specific to help me out.

I have dual tanks, one on each side. The guy I bought the truck from said to only use the passenger side tank. He didn't know why, but the guy he bought the truck from told him not to use the drivers side tank. All my vehicles have had the tank on the drivers side, so it annoys me that it's on the wrong side. Plus, at 10mpg, 15 gallons just doesn't get you that far.

I'm basically looking for some troubleshooting steps to try to figure out if the tank might leak, need a pump, solenoid, or something without filling up the tank with gas. I don't need to waste $50 if the tank leaks or whatever, and I lose the gas, or something doesn't work so the gas is stuck in there.

[tucsonjwt]

Just a few thoughts.
Before you do anything, get under the truck and see if the fuel lines going to/from the suspect fuel tank are all in place, with no suspicious hoses hanging down. If everything looks OK, then proceed to some tests.
With the engine on but truck not moving, push the selector switch to the left tank and see if you hear the characteristic buzz or hum sound which indicates that you have power to the switch and the valve. See if the fuel gauge drops to empty, indicating that the sending unit is working (at least while on empty.) If those two things check out OK, then you are on to the tank. I would put one gallon of fuel in the tank, then switch from the right to left tank with the engine running. Does the engine continue to run? If yes, then your fuel lines are intact and and everything is working. The last stop is the fuel tank itself - check to see if there is any discoloration on the outside of the tank, indicating that the tank was leaking.
If the tank has not been used in a long time, I would replace the soft rubber fuel lines as a precaution, since these lines do dry out and leak, especially at the clamps.
If the tank is leaking, then I would get a stock style replacement (about $100 or so for aftermarket). If you need a sending unit, be advised that the aftermarket ones (e.g. Spectra brand) will cause the fuel gauge needle to bounce when you accelerate/decelerate, brake, turn, etc.) The gauge will still be accurate, just bouncy. AC/Delco sending units likely will not do that, but they cost $140-$160 compared to about $40 for the Spectras.
If your need to replace the tank and/or sending unit you will have to drop the tank. Some posters prefer to lift the entire bed off the truck for easy access to the tank, others are OK with crawling under the truck, supporting the tank on blocks, then slowly lowering the tank to the ground.
I have dual tanks on my 83 C20 and also had them on my 76 C20, and they are handy when getting only 10 mpg (or less sometimes.) I never had the fuel tanks leak, but did replace sending units and selector switches. Of course, these were AZ desert trucks, so rust was not an issue.
I have some pics of the setup on my 83 C20, since it is a conversion dump bed and it is easy to see- if you want I can post them here.

[willstruck]

Thanks, that is exactly what I was looking for. I'll check it out, and post what I find. I'm pretty sure removing the bed is the best way, I've heard a lot of places do that instead of crawling under and/or dropping tanks.