Question 5
(a) List the two forms of cooling system employed in motor vehicle engines.
(b) (i) With the aid of a sketch, describe how the thermosyphon system operates
(ii) Label four parts of the sketch in (b)(i).
(c) Name the two types of thermostat used in a cooling system.
Observation
This question attracted a good percentage of the candidates. They perform well in parts (a) and (c) of the question. However part (b) was poorly responded to. The required response to part (b) is:
(b) (i) and (ii)
Thermosyphon cooling system: Arrows indicate coolant circulation. Note the height of the radiator compared with the engine.
Operation of a thermosyphon cooling system
Heat from the combustion of the charge is conducted through the walls of the cylinder to the water in cored passages surrounding these parts.
The cooling water, becoming less dense as it is heated, moves in a convection current towards the radiator header tank being displaced by colder and denser water from the radiator bottom tank. Passing downwards through the radiator core, the heat is transferred to the air current, created by the movement of the vehicle and generally assisted by a fan.