A temperature indicator is mounted on the instrument panel. It indicates the temperature of the water in the water jackets.
There are two types of temperature indicators
1. Mechanical type.
A mechanical type temperature indicator consists of a sealed bulb that fits in the cylinder head water jacket and is connected by a fine tube to a Bourdon type pressure gauge on the instrument panel.’ The bulb contains a volatile liquid that vaporizes when heated by the water in the jacket. The resulting gas pressure causes the panel gauge needle to move over a dial calibrated to read engine temperature.
In the electric type temperature indicator or Digital temperature indicators, the engine unit is connected to the panel unit by an insulated wire that receives current when the ignition switch is turned on. In one design, when the engine temperature increases, the current flowing through both units also increases. The increased current makes the panel unit (an electromagnetic device) to indicate a higher temperature. In another design, the engine unit decreases the current as of the temperature rises and causes the panel unit (a bimetal device) to indicate a higher temperature. The return circuit in both designs is through the ground connection.
In some designs, instead of needle movement, the green and red light systems are used to indicate engine temperature. When the engine temperature reaches normal, the green light circuit is completed by the engine unit and the dial indicates green light. When the engine is overheated, the engine unit completes the red light circuit and the dial indicates red light.
Watch how the temperature indicator works?
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