Temperature gauges and types of temperature gauges

These are generally provided on the engine as optional accessories. This seems to be only due to economic reasons, because the installation of the temperature gauge on the dashboard helps the driver to avert serious consequences, as he has before him the temperature indication all the time. 

Supposing the thermostat gets stuck up and does not open, the water circulation will stop and the engine temperature will go very high. However, if the temperature gauge is provided, the driver can stop the engine at once and remedy the situation, before the engine is overheated and some damage has already occurred.

Bourdon tube type

This has a bourdon tube inside, which is connected by a capillary tube to the element, containing some volatile liquid at a suitable temperature and which is inserted in the cooling water circuit at an appropriate point, generally on the engine side of the thermostat. 

As the temperature of cooling water increases, the liquid in the element evaporates and exerts its pressure in the capillary, which is further transmitted to the Bourdon tube. Due to this pressure, the Bourdon tube tries to straighten out and thus moves a pointer attached to it, to show higher temperature on the scale.

Electrically operated tube

This contains an element made of such a material that its electrical resistance decreases with the increase in temperature. The element is connected to the coils inside the dash unit while depicting the entire electrical circuit. The gauge element is inserted into the cooling water at some appropriate place. 

As the cooling water temperature increases, the resistance of the element decreases, which causes more current to flow in the coil, thus increasing the e.m.f. built up there. The pull of the coil on the armature carrying indicator pointer, therefore, increases and the pointer moves to show the higher temperature.