Temperature Gauge and Warning Light
The operator 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 occur.
Temperature gauges are of two general typesthe
balancing-coil (magnetic) type and the bimetal-
thermostat (thermal) type.
1. The 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.
2. The 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.
A temperature 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.
In some 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 starts.
Coolants and Antifreeze
Since water is easily obtained, cheap, and has the
ability to transfer heat readily, it has served as a basic
coolant for many years. Some properties of water, such
as its boiling point, freezing point, and natural corrosive
action on metals, limit its usefulness as a coolant. To
counteract this, use an antifreeze.
Antifreeze, usually ethylene glycol, is mixed with
water to produce the engine coolant. Antifreeze has
Prevents winter freeze up, which can cause
serious damage to the engine and cooling
Prevents rust and corrosion by providing a
protective film on the metal surfaces.
Lubricates the water pump, which increases the
service life of the pump and seals.
Cools the engine; prevents overheating in hot
For ideal cooling and winter protection, a 50/50
mixture of antifreeze and water is recommended. It will
provide protection from ice formation to about 34°F.
Higher ratios of antifreeze produce even lower freezing
temperatures; for example, a 60/40 mixture will protect
the cooling system to about 62°F. However, this much
protection is not normally needed.
Ethylene glycol is a toxic material- Avoid
prolonged skin contact or accidental ingestion.
Wear protective gloves and goggles while
handling antifreeze and coolants.
SERVICING THE LIQUID-COOLED
A cooling system is extremely important to the
performance and service life of the engine. Major
engine damage could occur in a matter of minutes
without proper cooling because combustion heat
collects in metal engine parts. This heat can melt
pistons, crack or warp the cylinder head or block, cause
valves to burn, or the head gasket to "blow." To prevent
these costly problems, keep the cooling system in good