Temperature Indicator Function | Temperature Indicator Types and Working Principle.

The temperature indicator function means the working process of the mechanical or electrical gauge in the car. In this article, I will discuss the temperature indicator function in detail.

Temperature Indicator Function

Temperature Indicator Function

A temperature indicator is mounted on the instrumental panel. Temperature indicators typically consist of a sensor, a sender unit, and the gauge itself. The sensor is responsible for measuring the engine’s temperature, and the sender unit then sends the information to the gauge on the dashboard.
Temperature indicators play a crucial role in vehicle maintenance and safety. They provide drivers with essential information about the engine’s temperature, allowing them to take appropriate actions if the engine starts to overheat. Overheating can lead to severe engine damage, and a functioning temperature indicator can help prevent such costly issues.
Temperature indicating system using cold and hot indicating lights.
Temperature indicating system using cold and hot indicating lights.


In some designs, instead of needle movement, a green and red light system is 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.
The temperature indicators indicate the temperature of the water in the water jackets. There are two types of temperature indicators available-
  1. Mechanical type temperature indicator.
  2. Electric-type temperature indicator.


Mechanical Type Temperature Indicator Function

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 instrumental panel. The bulb contains a volatile liquid that vaporizes when heated by the water in the jacket.
This resulting gas pressure causes the panel gauge needle to move over a dial calibrated to read engine temperature. 

The function of mechanical type temperature indicator

The mechanical temperature indicator operates on a simple yet effective principle. It consists of three main parts: a temperature sensor, a capillary tube, and a bourdon tube.
* Temperature Sensor: The temperature sensor is a small bulb or bulb-like component connected to the engine. It contains a special fluid, usually a mix of gas and liquid, which expands or contracts based on temperature changes.
* Capillary Tube: The capillary tube is a thin, flexible tube filled with the same fluid found in the temperature sensor. It acts as a conduit, allowing the fluid to flow between the sensor and the bourdon tube.
* Bourdon Tube: The Bourdon tube is a coiled, hollow tube that expands and contracts with the fluid’s movement from the capillary tube. This tube is connected to the indicator needle, which displays the temperature reading on the dashboard.
When the engine starts, the temperature sensor detects the temperature changes, causing the fluid inside to expand or contract accordingly. As the fluid moves through the capillary tube to the bourdon tube, it causes the tube to twist or straighten, depending on the temperature. This movement is then transmitted to the indicator needle, which points to the corresponding temperature on the gauge.

Electric Type Temperature Indicator Function

Electric type temperature indicator function


In the electric temperature indicator, 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) indicate a higher temperature. In another design, the engine unit decreases the current as 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. 

The function of an electric-type temperature indicator

The electric-type temperature indicator utilizes sophisticated electronic components to measure and display the engine’s temperature. Let’s break down its functioning:
* Temperature Sensor: The temperature sensor in an electric-type indicator is usually a thermistor or a temperature-dependent resistor. It is placed strategically within the engine or the coolant system, where it can detect changes in temperature accurately.
* Electric Circuit: The temperature sensor is connected to an electric circuit, which acts as a pathway for the flow of electric current. The resistance of the thermistor changes based on temperature fluctuations, causing variations in the electric current.
* Electronic Display: The electric circuit is connected to an electronic display on the vehicle’s dashboard. The display is often an LCD or LED screen that shows the temperature reading in real-time.
* Engine Control Unit (ECU) Integration: In many modern vehicles, the electric type temperature indicator is integrated with the Engine Control Unit (ECU). The ECU processes the data from the temperature sensor and uses it to manage engine performance, fuel injection, and other critical functions.


A temperature indicator in your car is more than just a gauge; it’s a crucial component for monitoring your engine’s health. 
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