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 types - the 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 5F to 10F 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 several functions.

Prevents winter freeze up, which can cause serious damage to the engine and cooling system.

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 weather.

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 -34F. Higher ratios of antifreeze produce even lower freezing temperatures; for example, a 60/40 mixture will protect the cooling system to about -62F. However, this much protection is not normally needed.

WARNING

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 SYSTEM

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 condition.