How to Change a GMC Pickup Gas Tank

by Christian Killian

Changing the gas tank on your GMC truck may be necessary if it becomes damaged or rusty. There are two steel straps that run under the tank and up to the frame rails of the truck for support. Dirt, water, and other debris can become trapped under these straps and cause the tank to leak. If this happens to your tank, you will need to replace it with a new tank. It is best to do this when the tank is empty, to minimize the weight of the new tank.

Step 1

Raise the rear of the truck with a jack and support it on jack stands. Be sure you are on solid, level ground so that the stands do not shift while you are working under the vehicle.

Step 2

Remove the hose clamp on the fuel filler neck and remove the rubber hose from the tank. You can use a screwdriver or a socket and ratchet if it will fit in the space around the tank.

Step 3

Support the tank with a floor jack and a large piece of wood. The tank may still be hard to balance during removal, so recruit a helper to assist you, if possible.

Step 4

Remove the bolts that hold the tank straps to the frame using a socket, ratchet and a long extension. The bolts may be rusted and thus hard to remove, but spraying them with a little penetrating oil can help to break them loose.

Step 5

Lower the tank down enough to get to the connection on the top of the tank. Remove the electrical connectors by unplugging them, and remove the fuel lines using a screwdriver to take off the clamps. Mark the lines so that you can reinstall them in the correct locations.

Step 6

Remove the tank from under the truck and remove the retaining ring on the top of the tank, where the sending unit or fuel pump assembly is located. The ring needs to be turned to the left, and often times you will need to use a screwdriver and hammer to spin it, especially if the tank is rusted or worn.

Step 7

Carefully lift the assembly from the old tank. Install it into the new tank by setting it into the hole provided, and install the new retaining ring and gasket that came with the tank. Be sure to orient the assembly just as it was in the old tank.

Step 8

Replace the tank straps with new ones if the old ones are rusty. There is a slot in the frame or cross member that the straps sit in. You will need to spin them 90 degrees to get them out and replace them.

Step 9

Raise the new tank into position under the truck. Attach the fuel lines and electrical connections to the sending unit and fuel pump assembly, making sure to put all the connections back in the correct positions.

Step 10

Raise the tank the rest of the way and install the tank straps with new bolts, if possible. Adding a little anti-seize compound to the bolts will keep them from rusting into the frame and save you time, should you ever need to remove the tank again.

Step 11

Install the fuel filler hose onto the nipple on the new fuel tank and secure it with a hose clamp. Make sure that you do not twist or kink this hose, or filling the tank will become a problem, as fuel will not properly flow through it.

Step 12

Add fuel to the tank and prime the fuel system by turning the key on and letting the fuel pump run briefly and then turning it off. Repeat this several times to be sure the pump has primed and filled the fuel lines with fuel.

Step 13

Test-run the truck and check for any leaks around your connections. If you find any, tighten the fittings or clamps prior to driving the truck.

Step 14

Remove the the truck from the jack stands and test drive the vehicle to ensure everything is working as intended. Fill the tank with fuel and you are done.

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