How to Replace a Boat Fuel Tank Sending Unit

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When the fuel gauge in a boat stops working, you might figure it's a gauge malfunction. Run down the connections from the tank to the gauge and check the gauge with an outside power source to make sure it's working. If it is, you'll have to replace the sending unit on the fuel tank.

Items you will need

  • Combination wrenches

  • Screwdriver

  • Rags

  • Acetone

  • Torque wrench

  • Putty knife

  • Oil-absorbent pads

Step 1

Remove the deck plate over the fuel tank with a screwdriver.

Step 2

Drain the fuel tank into an approved container. Place oil-absorbent pads around and under the container to contain any fuel spills.

Step 3

Remove the bolts from the flange of the sending unit and remove the sending unit from the tank. Inspect the fuel lines from the tank and, if necessary, replace with Coast Guard-approved fuel lines.

Step 4

Use a universal-style sending unit for a replacement and check if the new sender fits. Trim the channel if the channel and float arm are too large for the tank. Bend the float arm if necessary to avoid baffles within the tank or the tank walls. Bending the float arm within its original horizontal plane will have no effect on the accuracy of the gauge.

Step 5

Insert a clean rag into the opening for the sender to keep old gasket material out of the tank. Scrape off the gasket material from around the opening with the putty knife. Wipe the rim of the opening with acetone to remove any remaining material. Remove the cloth from the opening.

Step 6

Press the new gasket onto the bottom of the new sending unit, making firm contact with the flange around the bottom of the unit. Insert the sending unit float-first into the opening. Dab a gasoline-proof screw adhesive onto the threads of the sending unit bolts and insert them into the hole, tightening them to the torque recommended by the sending unit manufacturer.

Step 7

Connect the wire from the fuel gauge to the post on the sending unit that is marked with the letter S. Connect the other post on the sending unit, which is marked with a "minus" sign, to the boat's common ground.


  • Working with gasoline is dangerous. Flames, sparks or smoking in the area are absolute no-nos.
  • A well-ventilated area is a must.