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Old 11-04-2020, 11:14 AM   #1
rgano's Avatar
City: Southport, FL near Panama City
Vessel Name: FROLIC
Vessel Model: Mainship 30 Pilot II since 2015. GB-42 1986-2015. Former Unlimited Tonnage Master
Join Date: Oct 2007
Posts: 4,488
Troubleshooting KUS fuel level sender

I received an email this morning from KUS which directed me to their blog. I thought this lift from their blog might be of interest to those out there concerned about what they are seeing on their fuel gauges. I have been through the replacement of three failed level gauges on this boat and found their troubleshooting advice useful.

How a Fuel Level Sender Works
The fuel level sender, also referred to as a fuel level sensor or sending unit, is connected to the fuel gauge by a sender wire. It is also attached to a float, which moves with the fuel level in the tank (It works a bit like a float in the tank of a toilet). Together, this assembly tells your fuel gauge how full the tank is. The sender changes resistance, measured in ohms as the fuel level drops and the float descends. Changes in resistance move the gauge needle.

Itís a good idea to familiarize yourself with these parts before they cause problems. Look for a small, round plate at the top of your boatís fuel tank. You will often get to it through a deck plate at the aft end of the tank.

Fuel Sender Installed In Tank
Fuel Sender Installed In Tank
Your fuel sender will have either two or three connections. For the three connection type, one wire runs to the gauge, another wire connects to the power supply, and the last wire connects to the ground or the negative side of your battery. For the two connection type, one wire runs to the gauge, where it draws power and sends you your fuel level signal, and another wire connects to the ground.

How to Know the Sender is Faulty
As we said above, you may have a bad fuel level sender if you run out of gas when your gauge says you have plenty left. A fuel sensor issue may also cause:

The fuel gauge needle to become stuck on full or empty
The fuel gauge needle to bounce erratically from one reading to another (this can happen for short senders, not really a bad sender)
Before attempting any troubleshooting or part replacement, make sure you are confident and knowledgeable in what youíre doing. Exercise EXTREME CAUTION when working around fuel tanks. If you are inexperienced with boat repair, itís a good idea to take your boat to a marine repair facility or boat dealership service department.

First, you will want to rule out other causes of an inaccurate fuel gauge reading.

Confirm that the gauge is receiving power
Check whether the needle on the gauge is physically stuck due, perhaps, to moisture or rust
Disconnect the sending wire and the gauge should move immediately to ďfullĒ; if so, the gauge is not the source of the problem
Test the sender wire with an ohms multimeter to rule out a wiring problem
If you proceed through all of the above and still see an issue, the fuel level sender is probably damaged. Remember, itís possible that the sender and the gauge both need to be replaced.

Troubleshooting Your Fuel Level Sender
Once you narrow down the source of your issue to the fuel level sender, perform the following steps to learn whatís wrong with it.

Check to see if you have power from the gauge to the sending unit (black wire). The reading at the sending unit (black wire) will be less than the input voltage on the gauge (red wire).
Check the sending unit ground (pink or blue wire). The pink or the blue wire must be properly grounded to a common ground or to the negative side of your battery.
To check the sending unit operation, turn all power to your gauge off, and disconnect the sender wires at the sending unit (You may need to cut and reconnect the wires later.)
Remember, if your tank is not rectangular, you are reading liquid level, not gallonage. Put an ohmmeter on the two disconnected sender wires and take a reading:

For the standard American version sender (240-30 ohms), you will have between 232 to 252 ohms @ empty, and 28 to 36 ohms @ full.
For the standard European version sender (0-180 ohms), you will have between 0 to 2 ohms @ empty, and 171 to 192 ohms @ full.
If you do not know the liquid level in your tank, you will need to remove the sending unit from the tank. Once the sending unit is removed, slide the float up and down, and verify the above-mentioned readings with an ohmmeter.

You may be able to fix your issue by replacing faulty wires. If not, itís time for a replacement. Marine fuel level senders do not last forever, and lesser quality ones will likely fail sooner than others.
Rich Gano
FROLIC (2005 MainShip 30 Pilot II)
Panama City area
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