Diagnose Remote Fuel Tank Level Gauge Error

[cneames]

The [remote electrical fuel tank level] gauge on [my 2002 OUTRAGE 230] boat reads 3/4-FULL and is not moving. While showing 3/4-FULL tank, I added 110 gallons on my last fill-up and [the tank level indicator] did not move. The wires between the tank sender and the gauge look to be in decent shape. When I unplug the pink wires from the sender [the reading on the tank level gauge] drops to [EMPTY].

Q1: is [the remote electrical gauge reading changing to EMPTY if the pink wires to the tank sender are disconnected] an indication of a bad sender or gauge?

Also, I am having trouble identifying which sender to replace [the suspected bad sender]--with indeed [a new sender] is needed.

ASIDE
The boat has a Yamaha engine of 225-HP and digital Yamaha gauges.

[Moderator's Note: this thread is moving to SMALL BOAT ELECTRICAL for discussion.]

[jimh]

Q1: is [the remote electrical gauge reading changing to EMPTY if the pink wires to the tank sender are disconnected] an indication of a bad sender or [an indication of a bad] gauge?

The inference from your test is the remote electrical tank level gauge MAY BE working properly, because the tank level indication changes when the circuit resistance changes (from some unknown resistance in the sender with a value associated with 3/4-FULL tank level) to open circuit (a value which is akin but much higher--infinite resistance--to the expected resistance of 240-Ohms).

A better test of the remote tank level gauge would be to connect a known resistance to the pink wires, and check the gauge reading. The typical range of resistance of a tank level sender is given in an article at

Tank Sender and Trim Sender Resistance
https://continuouswave.com/forum/viewto ... f=9&t=3043

where the following standard values are specified:

• 33-Ohm = FULL
• 103-Ohm = HALF
• 240-Ohm = EMPTY

To perform a test, you need a method of creating a device that will mimic the resistance of a tank level sender. Three resistors of the values 33-Ohms, 100-Ohms, and 220-Ohms, which will correspond approximately to the sender resistances expected for FULL, 1/2-FULL, and EMPTY, can be used to simulate a properly-working tank level sender. Connect one resistor at a time between the two PINK wires and the BLACK wire--see note on wire colors below--and observe the remote gauge reading. With those three resistors you can also simulate other values:

• 100-Ohm in series with 33-Ohm = 133-Ohm;
• 100-Ohm in parallel with 220-Ohms = 68.75-Ohm;
• 220-Ohm in series with 33-Ohm = 253-Ohm

This should give you five test points with the following indications:

• 33-Ohm = FULL
• 68.75-Ohm = between HALF and FULL
• 100-Ohm = HALF-FULL
• 133-Ohm = below HALF-FULL
• 220-Ohm = very nearly EMPTY
• 253-Ohm = EMPTY

Another test will be to connect an Ohmmeter to the tank level sender, and note the resistance reading. Then operate the boat and engine for enough time that a significant amount of fuel is consumed and the tank level must have changed. Then measure the resistance reading of the sender.

If there has been no change in the resistance reading of the tank level sender, then a reasonable inference is the tank level sender is stuck in some position and the resistance of the sender is not changing as the tank level changes.

A reasonable first step in further action would be to carefully remove the existing fuel tank level sender and examine it for a mechanical problem that is preventing the sender resistance from changing with tank level.

A good source for information about obscure OEM parts in a Boston Whaler boat is by contacting your local Boston Whaler dealer. If you local Boston Whaler dealer is not interested in helping you obtain an OEM replacement part, contact Sue Lodel a using the contact information at

Latest Twin Cities Marine, Sue Lodel Contact Information
https://continuouswave.com/forum/viewto ... 706#p46706

WIRE COLOR
In the typical use of wire insulation color to identify the function of an electrical wire, the color PINK is used for the connection from the remote electric tank level gauge to a resistive fuel tank level sender, and a BLACK conductor then completes the circuit to the battery negative. In some pre-wired boats, notably certain Boston Whaler boats, there may be two PINK conductors attached to the resistive fuel sender at the fuel tank location. One PINK conductor may be routed to the helm location, where it could become part of the circuit for an electric remote fuel tank level gauge, if a gauge of that type were to be installed; the other PINK conductor may be intended to be routed to a second circuit that might be part of a Mercury OptiMax engine, but the exact purpose for that conductor is unkown to me. For more information read the thread

Fuel Tank Level Sender Wiring
https://continuouswave.com/forum/viewtopic.php?t=8105

In that thread follow the link to an attached file in PDF format that shows in detail the wiring schematic diagram for a "190NT" model Boston Whaler boat. Boston Whaler uses the code NT to refer to NANTUCKET, a model name they used for a model similar to the OUTRAGE that was available in c.2003

The test resistors should be connected at one end to the PINK conductor that is feeding the suspected-bad tank level indicator gauge, and the other end to the GREEN conductor (or perhaps a BLACK conductor) at the fuel tank sender location, but without any connection during the test to the existing tank level sender circuit at the fuel tank. The test resistor takes the place of the sender resistance, so the in-tank sender must not be connected to the PINK conductors during the test.

If the second PINK conductor is not being used for any purpose, it should also be check to see if it has become inadvertently connected in some way to the battery negative circuit, such as perhaps via corrosion, which would create a second path to ground and affect the gauge reading significantly. In fact, this might be the FIRST THING to try as a remedy to the tank level gauge indicator error.

[cneames]

Fantastic information! Thank you!

[jimh]

I added some more details about where the test resistors should be connected to my earlier reply. The two PINK conductors go to one end of the test resistor and the other end of the resistor goes to the battery negative or BLACK conductor or a GREEN ground conductor, which should also be at the fuel tank. Also, check the connection of the PINK conductor that is NOT the one going to the helm for the tank level gauge. If it has become inadvertently connected to ground in some manner, it could be affecting the gauge reading. If that PINK conductor is not being used with an OptiMax engine or some other device, there is no need for it to be connected at the tank level sender.