Monaco Fuel gauge FULL all the time

Monaco sending units have a calibration POT screw. You fill the tank full and then SLOOOOWLY turn the Pot screw in very small increments until the needle is straight on the full mark. It takes up to 1 minute per adjustment to get the correct reading. So, you cannot use any sending unit. Doug

The Centroid fuel sender has no moving parts. It works by measuring capacitance,
an electrical property, between its inner and outer tubes in the tank. The more fuel
between the tubes, the higher the reading. Electronics in the hockey-puck head of
the sender convert the capacitance to current to drive the fuel gauge.
Connections:
The Centroid sender has four connections:
• Positive and Negative: Battery voltage to run the electronics in the
sender head.
• Send: Connects to the Send terminal of the gauge on the dash.
• Alarm: Makes a connection internally to the Negative terminal when the low
alarm fuel level is reached (when gauge is reading about 1/8 tank). This turns
on the alarm light on the dash. It is not adjustable.
Checking the Gauge:
• Remove the SEND wire from the Sender. Turn the ignition power ON. The
fuel gauge should read above FULL.
• Touch the SEND wire to the NEGATIVE terminal of the sender. When the
ignition Power is applied, the gauge should read EMPTY.
• If this test passes, place the send wire back on the SEND terminal of the
sender.
Checking the Voltage:
• Place the BLACK lead of the voltmeter on the sender NEGATIVE terminal.
• Place the RED lead of the voltmeter on the POSITIVE terminal of the
sender.
• Reading of the voltmeter should be about 12 Volts DC.
• Place the RED lead of the voltmeter on the SEND terminal of the sender.
• Reading of the voltmeter will range between Zero and 9 Volts DC.
Calibration and Adjustments:
• Calibration and adjustments to the fuel sender must be performed with the
engine running since this affects the voltage at the sending unit.
There are Two Adjustments on the Centroid Sender:
• Empty: Adjusts for length of sender, should be sealed with a brown sealant,
stating that the sending unit is factory adjusted. If the sealant has been
tampered with, the sending unit may have an incorrect calibration. Do not
change if the sealant is intact.
• Full Adjustment: The full adjustment can be used to correct for slight
differences between fuel meters. During installation, it has been calibrated
for your meter and should not need readjustment.

NOTE: Calibration procedures should be performed by a qualified
service technician. Calibration procedure will require both Empty and
Full potentiometers be adjusted.
Proper calibration is performed by calibrating the Empty side first, then the Full
side. Ensure the Fuel Tank is full prior to performing the following procedure.
1. Setting Empty:
• Place the sending unit in two inches of clean diesel fuel.
• Rotate both the full and empty potentiometers fully clockwise.
• Slowly adjust the Empty potentiometer counterclockwise until the needle on
the gauge just covers the empty mark.
• Rotate the potentiometer back clockwise slightly and then counterclockwise
to Empty ensuring the needle on the gauge is not below empty. The sender
will not show anything below the Empty mark.
2. Setting Full:
• Put sending unit in the full tank of fuel.
• Slowly turn Full potentiometer counterclockwise until the needle on the
gauge is down to the full mark.
Both adjustments should be verified several times to ensure proper calibration.
The key for proper adjustment technique is to start with the full adjustment screw
fully clockwise, and with a full tank of fuel. This causes the readings to be above
marks. Slowly adjust counterclockwise until the marks are reached. The intent is
to always adjust downscale rather than upscale.
Troubleshooting:
A. Fuel Only: One possibility, when there is a constant above full reading,
may be water in the bottom of the fuel tank. The sender will not work
correctly in conducting fluids such as water (it will read above full all
the time in water).
B. Electronic Output: The sender has a transistorized output. This prevents
an ohmmeter from getting a correct reading of its output resistance.
C. Contact Centroid: Probably 90% of the returns Centroid tests work
okay on the bench. If you have incorrect readings contact Centroid
(telephone: 800-423-3574 or, preferably, fax: 904-423-3709) with the
symptoms. A short,"fill in the blanks" troubleshooting test is provided,
appropriate to the sender. It is easier to find the problem that way than
after the sender has been removed from the system, since the problem
is not necessarily with the sender.
NOTE: Sending units are calibrated by length from the manufacture. If
replacing a sending unit and the sender needs cut, the empty setting will
require being set first

dougrainer wrote:
Monaco sending units have a calibration POT screw. You fill the tank full and then SLOOOOWLY turn the Pot screw in very small increments until the needle is straight on the full mark. It takes up to 1 minute per adjustment to get the correct reading. So, you cannot use any sending unit. Doug

Yes I tried that, nothing moves.

dougrainer wrote:
The Centroid fuel sender has no moving parts. It works by measuring capacitance,
an electrical property, between its inner and outer tubes in the tank. The more fuel
between the tubes, the higher the reading. Electronics in the hockey-puck head of
the sender convert the capacitance to current to drive the fuel gauge.
Connections:
The Centroid sender has four connections:
• Positive and Negative: Battery voltage to run the electronics in the
sender head.
• Send: Connects to the Send terminal of the gauge on the dash.
• Alarm: Makes a connection internally to the Negative terminal when the low
alarm fuel level is reached (when gauge is reading about 1/8 tank). This turns
on the alarm light on the dash. It is not adjustable.
Checking the Gauge:
• Remove the SEND wire from the Sender. Turn the ignition power ON. The
fuel gauge should read above FULL.
• Touch the SEND wire to the NEGATIVE terminal of the sender. When the
ignition Power is applied, the gauge should read EMPTY.
• If this test passes, place the send wire back on the SEND terminal of the
sender.
Checking the Voltage:
• Place the BLACK lead of the voltmeter on the sender NEGATIVE terminal.
• Place the RED lead of the voltmeter on the POSITIVE terminal of the
sender.
• Reading of the voltmeter should be about 12 Volts DC.
• Place the RED lead of the voltmeter on the SEND terminal of the sender.
• Reading of the voltmeter will range between Zero and 9 Volts DC.
Calibration and Adjustments:
• Calibration and adjustments to the fuel sender must be performed with the
engine running since this affects the voltage at the sending unit.
There are Two Adjustments on the Centroid Sender:
• Empty: Adjusts for length of sender, should be sealed with a brown sealant,
stating that the sending unit is factory adjusted. If the sealant has been
tampered with, the sending unit may have an incorrect calibration. Do not
change if the sealant is intact.
• Full Adjustment: The full adjustment can be used to correct for slight
differences between fuel meters. During installation, it has been calibrated
for your meter and should not need readjustment.

NOTE: Calibration procedures should be performed by a qualified
service technician. Calibration procedure will require both Empty and
Full potentiometers be adjusted.
Proper calibration is performed by calibrating the Empty side first, then the Full
side. Ensure the Fuel Tank is full prior to performing the following procedure.
1. Setting Empty:
• Place the sending unit in two inches of clean diesel fuel.
• Rotate both the full and empty potentiometers fully clockwise.
• Slowly adjust the Empty potentiometer counterclockwise until the needle on
the gauge just covers the empty mark.
• Rotate the potentiometer back clockwise slightly and then counterclockwise
to Empty ensuring the needle on the gauge is not below empty. The sender
will not show anything below the Empty mark.
2. Setting Full:
• Put sending unit in the full tank of fuel.
• Slowly turn Full potentiometer counterclockwise until the needle on the
gauge is down to the full mark.
Both adjustments should be verified several times to ensure proper calibration.
The key for proper adjustment technique is to start with the full adjustment screw
fully clockwise, and with a full tank of fuel. This causes the readings to be above
marks. Slowly adjust counterclockwise until the marks are reached. The intent is
to always adjust downscale rather than upscale.
Troubleshooting:
A. Fuel Only: One possibility, when there is a constant above full reading,
may be water in the bottom of the fuel tank. The sender will not work
correctly in conducting fluids such as water (it will read above full all
the time in water).
B. Electronic Output: The sender has a transistorized output. This prevents
an ohmmeter from getting a correct reading of its output resistance.
C. Contact Centroid: Probably 90% of the returns Centroid tests work
okay on the bench. If you have incorrect readings contact Centroid
(telephone: 800-423-3574 or, preferably, fax: 904-423-3709) with the
symptoms. A short,"fill in the blanks" troubleshooting test is provided,
appropriate to the sender. It is easier to find the problem that way than
after the sender has been removed from the system, since the problem
is not necessarily with the sender.
NOTE: Sending units are calibrated by length from the manufacture. If
replacing a sending unit and the sender needs cut, the empty setting will
require being set first

Thanks, I will try these test.

Kidoo wrote:

dougrainer wrote:
Monaco sending units have a calibration POT screw. You fill the tank full and then SLOOOOWLY turn the Pot screw in very small increments until the needle is straight on the full mark. It takes up to 1 minute per adjustment to get the correct reading. So, you cannot use any sending unit. Doug

Yes I tried that, nothing moves.

Then, BAD sending unit. Doug

My Monaco has the same problem but sometimes it works. Most times it does not. It holds 100+ gal so I just fill it every 500mi or so.