A fuel sending unit is a critical component in the operation of a vessel. Improperly functioning sending units will provide false fuel readings putting you and your passengers at risk of running out of fuel. The process of determining faults, testing, and replacing the unit is straightforward. When it comes to boat repair, what is a fuel sending unit?

What Is A Fuel Sending Unit

The sending unit is an instrument that measures the amount of fuel remaining in a diesel or gasoline tank. 

A float slides up and down a shaft depending on the fuel level. At that point, an electrical signal is sent to the fuel gauge, which reflects the amount of gas or diesel remaining in the tank to alert the driver. 

What Are The Symptoms Of A Bad Fuel Sending Unit

There are three symptoms commonly associated with a faulty sending unit that are easily recognizable. 

First, the fuel gauge bounces erratically between full and empty.

Secondly, the tank reads as empty despite being full.

Lastly, vice versa, the tank reads full despite being empty.

How Do You Test A Boat Fuel Sending Unit

There are a couple of ways to test a fuel sending unit. A single tool makes the job far more straightforward. Purchase or pull a multimeter out of your toolbox.

The first method is to test the wires running into the fuel gauge. With the ignition on, set the meter to 20V DC. Measure the amount of power running from the sending unit to the power connection in the fuel meter. The meter should be reading 12 volts.

A second but more time-consuming method is measuring the ohms. However, first, you will need to learn the ohm reading standard for the particular sending unit. 

With the ohm setting in position on the multimeter, slide the float up and down and note the ohm reading on the upper and lower ends. If the ohms reading does not move or is out of the standard range, the sending unit requires replacement. 

How Much Does A Fuel Sending Unit Cost

On average, a fuel sending unit for a boat ranges between 30 and 70 dollars. The range in cost is due to the length of the fuel sending unit needed.

Fuel tanks range in size, which is dependent on how large the vessel measures. Boat’s which are longer in heavier are equipped with large tanks due to burning fuel at a higher. Additionally, the capability to hold more fuel equals extended run times verse those with small onboard tanks.

The size and, most importantly, the depth of the take will dictate the cost of the sending unit. Therefore, the cost to purchase a fuel sending unit on a big vessel will be higher.

Replacing a fuel sending unit is straightforward and can be accomplished by boaters who are slightly handy. However, marine repair centers are experienced in replacement. Expect to tack on an extra 200 dollars in labor. You might want to consider doing this yourself.

Major marine parts suppliers such as West Marine stocks sending unites. The best bet is to remove the part and bring it into the shop to match the size. 

How Do You Replace A Fuel Sending Unit In A Boat

Replacing a sending unit is straightforward but must be done carefully and slowly to avoid costly mistakes.

Locating The Sending Unit

The biggest challenge is locating the unit. Walk the deck towards the vessel’s rear and keep an eye out for a small circular hatch. 

Once the access port is found, remember that it does not contain a release, it must be lifted open with a flathead screwdriver. Peek inside with a flashlight and look for a circular plate with screws and wires coming from the top.

Steps To Remove The Sending Unit From A Boat

First, have all of the necessary tools on hand. The tools include a phillips head screwdriver, wire cutters, crimping tool, damp rage, and butt connectors that match the wire gauge.

Clean any debris that is sitting on top of the unit. Dirt that is not removed may fall into the tank and contaminate the fuel.

Unscrew the unit and place the screws in a safe place where they will not become lost. 

Slowly lift the fuel sending unit out of the tank along with the gasket that sits between the tank’s surface and the screw plate.

Label and cut the wires. Most importantly, leave enough wire length to be able to connect the replacement unit. 

If you are unsure about the replacement size, bring the sending unit to a marine shop as a comparison. Cover the open of the tank while you are shopping.

Steps To Replace A Sending Unit In A Boat

Inspect the new unit to be sure that no packaging debris remains.

Place the gasket on the top of the fuel tank lining up the screw holes.

Lower the sending unit into the tank to become flush with the tank while lining up the screw holes.

Run the screws by hand through the top of the sending unit, through the adequately aligned gasket, and into the tank in a star pattern. Avoid overtightening the screws.

Connect the labeled wires by placing the sending unit wires in the butt connectors with the correct wires leading off the fuel gauge. Crimp each connection and ensure the wires are snugly fit. When possible, heat shrink the contacts to avoid corrosion.

Replace the deck hatch.

Test the fuel gauge to ensure it is now reading correctly.

Do you have a Faulty Sending Unit?

When you feel that your fuel level readings are out of whack, it is time to test the sending unit. Avoid putting yourself at risk of inadvertently running out of fuel. Fortunately, boat sending units are easy to replace and are low in cost. To keep your readings accurate, test and replace.