magnetic field produced by the "hot" coil is negligible. At
this time the pointer and armature assembly will align
itself with the resultant magnetic field produced by the
"cold" and bucking coils at the 1 00°F position. The
mag-netic field of the "cold" and bucking coils is always a
constant and serves as a reference. As the temperature
of the liquid increases, the resistance of the sender
decreases since the thermistor has a negative tempera-
ture coefficient. The decrease in sender resistance in-
creases the current flowing in the "hot" coil, reaching a
maximum at the full-scale position. Thus, the interaction
of the magnetic fields of the three coils produces a
resultant magnetic field which controls the rotation and
position of the armature and pointer assembly.
NOTE - The gauge is grounded to chassis through
Instrument cluster printed circuit.
Figure 19 - Water Temperature Gauge Circuit Diagram
The sender terminal is the first terminal clockwise from
ground terminal (when viewed from back side). The
ignition terminal is directly opposite from sender terminal.
Disconnect sender wire from water temperature
Connect one lead of gauge tester to sender wire.
Connect other lead of tester to a good vehicle
ground. (Gauge tester now substitutes for sender
Turn key switch "ON" (Be sure there is power to
Set tester: For 260° gauges, use 55 ohms. For 2200
gauges, use 99 ohms. Temperature gauge should
read at full scale (HOT). (Pointer within 2 pointer
widths of hash mark.
Set tester: For 2600 gauges, use 113 ohms. For
2200 gauges, use 212 ohms. Gauge should read at
half scale. (Pointer within 2 pointer widths of hash
Set tester to 1365 ohms Gauge should read at low
scale (COLD). (Pointer within 2 pointer widths of
If temperature gauge responds correctly to various tester
settings, gauge and wiring between gauge and sender
unit are OK.. Trouble is in sender unit or sender unit is
NOTE - Sealant or dirt on threads of sender unit or
engine cylinder head may prevent a good electrical
ground Check for this condition before replacing
If gauge does not respond to tester:
Check continuity of gauge wiring circuits. Make
sure connectors' terminals are clean and tight.
Check gauge cluster ground circuit. Make sure
circuit is grounded.
If wiring is OK, replace gauge.
A similar procedure is used to test engine, transmission
and rear axle oil temperature gauges. Refer to Table 1
for tester settings.
AUXILIARY TEMPERATURE GAUGES
The auxiliary (optional) temperature gauges are also
electromagnetic type and are actuated by sending units
(variable resistance thermistors). Sending units are
located in the component on which temperature
monitoring is desired (engine oil, transmission, rear
axles, etc. Operating principles and testing of auxiliary
temperature gauge previously described. Refer to Table
1 for tester settings for checking these gauges.
CTS-4140Y - Page 11