Temperature Gauge and Warning
should be warned if the temperature of the coolant in the cooling system goes too high.
For this reason, a temperature gauge or warning light is installed in the instrument panel
of the vehicle. An abnormal heat rise is a warning of abnormal conditions in the engine.
The warning lights alert the operator to stop the vehicle before serious engine damage can
gauges are of two general typesthe balancing-coil (magnetic) type and the
bimetal-thermostat (thermal) type.
balancing-coil consists of two coils and an armature to which a pointer is attached. An
engine-sending unit, that changes resistance with temperature, is placed in the engine so
that the end of the unit is in the coolant. When the engine is cold, only a small amount
of current is allowed to flow through the right coil; the left coil has more magnetism
than the right coil. The pointer, attached to the armature, moves left indicating that the
engine is cold. As the engine warms up, the sending unit passes more current. More current
flows through the right coil, creating a stronger magnetic field. Therefore, the pointer
moves to the right to indicate a higher coolant temperature.
bimetal-thermostat is similar to the balancing-coil type except for the use of a bimetal
thermostat in the gauge. This thermostat is linked to the pointer. As the sending unit
warms up and passes more current, the thermostat heats up and bends. This causes the
pointer to swing to the right to indicate that the engine coolant temperature is rising.
warning light informs the operator when the vehicle is overheating. When the engine
coolant becomes too hot, a sending unit in the engine block closes, completing the circuit
and the dash indicating light comes ON. The indicating light warns of an overheating
condition about 5°F to 10°F below coolant boiling point.
construction equipment a "prove-out" circuit is incorporated in the system. When
the ignition switch is turned from OFF to RUN, the light comes on, proving that the system
is operating. If the light does not come on, either the bulb is burned out or the sending
unit or connecting wire is defective. The light will go out normally after the engine