The design and operating principle of the cooling system (Mercedes-Benz S-Class W126)

All engines have a closed cooling system under pressure. Because of this, the boiling point rises to approximately 118°C. When using a coolant with a freezing point of -30°C, the boiling point rises to approximately 125°C. The red area on the temperature gauge starts at 115°C. Under severe driving conditions (driving uphill, at high speed, in a column, at high cooling air temperature) the coolant temperature gauge needle can reach the red area without causing engine damage. When driving further, it is useful to move the gearshift lever to the "N" position in cars with automatic transmission and avoid heating the coolant due to the presence of a gearbox radiator.

The circulation of the coolant is regulated by a thermostat. As long as the engine is cold, the coolant circulates not only in the cylinder head, but also in the engine block when the heating is on - in the heater heat exchanger. As the temperature increases, the thermostat opens a large circle of coolant circulation. The liquid is driven through the radiator by a constantly running coolant pump. The liquid flows through the radiator from top to bottom and is cooled in the finned tubes of the radiator by the passing air. The fan behind the radiator serves to ensure sufficient air flow, while an additional air flow created during movement passes through the radiator.

Cooling diagram of 8-cylinder engines

Cooling diagram of 6-cylinder engines

Coolant pump and thermostat housing (8-cylinder engine)