Replacing Your Boat's Fuel Sending Unit: A Step-By-Step Guide

If your boat's fuel gauge is not working, it may be time to replace the fuel sending unit. This is a common problem with a relatively simple solution. The fuel sending unit is attached to the fuel tank by five bolts, which should be carefully removed. It is important to work in a well-ventilated area and ensure that the boat is level before beginning this process, as there is a risk of gasoline spillage. Once the bolts are removed, the sending unit should be pulled out, and a new gasket should be installed. It is also recommended to check the wiring to ensure that the ground wires are not causing any issues. With the right tools and precautions, replacing a fuel sending unit on a boat can be a straightforward task.

Disconnect the battery and ensure the boat is well-ventilated

Disconnecting the battery is an important safety precaution when working on a boat's fuel system. This will eliminate the risk of sparks that could potentially ignite fuel vapours. It is also a good idea to ensure that the boat's battery switch is turned off.

Before beginning any work, it is crucial to ensure the boat is well-ventilated. This will help to prevent the buildup of dangerous fuel vapours. Working outdoors is ideal, but if that is not possible, make sure the work area is adequately ventilated. Open all hatches, windows, and doors to create cross-ventilation. If possible, use fans to increase airflow and direct fumes away from the work area.

Additionally, it is important to avoid any sources of ignition, such as lit cigarettes or open flames, when working on a boat's fuel system. It is also recommended to clean the area around the fuel tank and sending unit to remove any built-up grease or grime, which could pose a fire hazard.

By taking these precautions, you can create a safer work environment and reduce the risk of fire or explosion when working on the fuel sending unit. These steps are crucial to ensuring your safety and the safety of those around you.

Remove the bolts and detach the sending unit

To remove the bolts and detach the sending unit, you will need to first disconnect the battery and ensure you are working in a well-ventilated area. It is also important to ensure that the boat is level and that the tank is not full to avoid spilling fuel. Clean the top of the tank near the sending unit and remove the bolts holding the sending unit in place. Note that there may be five bolts that are not equally spaced, so you will need to be patient and careful when removing them. Stuff a rag into the hole to prevent anything from falling in. Pay attention to the orientation of the sending unit and the direction the float arm is facing. Measure the distance from the top of the sending unit to the bottom of the tank to ensure you get the correct length for the replacement sending unit.

Clean the tank and check the gasket

To clean your boat's fuel tank, you should begin by draining the tank. If you have a removable gas tank, you can simply empty it out. If your tank is fixed, angle the boat so the gas moves to one side of the tank, and use a gas siphon to drain the tank. Remove the fuel cap and plug any vent piping. Place a chemical-safe container under the other end of the hose, pump the siphon, and allow all the gas to drain. Dispose of the old gas properly as it is toxic.

Next, disconnect the gas line to the boat engine. Before adding any cleaning chemicals, ensure that the gas line is disconnected. Check your boat manual to learn how to isolate the gas line.

Now, it's time to clean the tank. You can use a pressure washer on its lowest setting to blast water into the tank, removing dirt, grime, and debris. Use the siphon or tip the tank to dump the water out, and repeat until the water is clear.

Alternatively, you can use a cleaner like Sea Foam Engine Cleaner or isopropyl alcohol to remove the sludge. Pour in about 3/4 of a can of Sea Foam or fill the gas tank 2/3 of the way up with alcohol. Allow it to sit in the tank for 15 minutes to several hours, then dump or siphon the cleaner into a chemical-safe container.

Before reassembling, check and change the fuel filter, and wipe down the gas tank with a lint-free towel. If your tank is removable, allow it to dry in the sun with everything open for a few hours.

Finally, reconnect the fuel lines and other parts, and remove any plugs in vents. You can add an evaporator product along with fresh fuel if you are worried about any moisture.

To check the gasket, begin by removing the wires from the sending unit and checking the gauge. If the sending unit is bad, replace it and clean the area. Apply a non-hardening petroleum product like Hylomar or Permatex to the gasket. Tighten the screws/bolts evenly and do not over-torque to avoid distorting the gasket.

Measure the tank depth to get the correct length for the new sending unit

To replace the fuel sending unit on your boat, you'll need to start by measuring the tank depth to get the correct length for the new sending unit. This measurement will determine the length of the sending unit's float arm.

First, locate the top of the tank and the sending unit. The sending unit is usually attached to the tank with bolts. Once you've located the sending unit, measure the depth of the tank from the top near the sending unit to the bottom.

Next, you'll need to trim the sending unit arm to match the tank depth. Sending unit kits usually come with a 24-inch arm, which you can cut to size using wire cutters or a hacksaw, depending on the kit.

After trimming the arm to the correct length, fasten it securely to the flange of the new sending unit with setscrews. The flange will be screwed into the top of the tank, so it's important to ensure a tight fit.

Now you're ready to move on to the next steps of replacing the fuel sending unit, which may include disconnecting wires, removing the old sending unit, and installing the new one.

Reinstall the new sending unit and reconnect the battery

Now that you have removed the old fuel sending unit, cleaned the area, and prepared the new sending unit, it's time to install the new one.

First, ensure that the new sending unit is the correct size for your tank. The length of the sending unit depends on the depth of your tank. For plastic tanks, subtract 1 inch from the depth, and for metal tanks, subtract 0.5 inches. It's important to get the right size to ensure accurate fuel level readings.

Next, align the gasket that came with the new sending unit. The gasket holes should match the screw holes on the tank. Mark both the gasket and the tank with a sharpie to ensure proper alignment. The sending unit should only fit in one orientation, so make sure it's positioned correctly.

Once the gasket is in place, attach the sending unit to the tank using the provided screws. Be careful not to over-tighten the screws, as this can distort the gasket and affect the seal. If your sending unit came with different types of screws, make sure to use the ones that fit your sending unit properly.

Now, adjust the float arm on the sending unit. It should be facing toward the center of the tank and should not rub against the side of the tank. The float arm can usually be adjusted in 90-degree increments. Refer to the instructions that came with your sending unit for specific adjustment instructions.

Finally, reconnect the battery and test the fuel gauge to ensure it's working properly. Make sure to follow any additional instructions or safety precautions provided by the manufacturer of your new sending unit.

Frequently asked questions