Answer for what is Thermosiphon System in engine

In this system pump is not used. This type of cooling system is based on the scientific principle that hot water is lighter than the cold one. Hot water rises and cold water settles in the bottom. Water heated by the engine rises within it and flow to the top of the radiator where it is cooled; by the time Cooling System it reaches the bottom of the radiator it is relatively cool and starts on its round again.