Engine cooling function

P20.00-2333-79

1 Coolant feed pipe for cooling circuit

2 Coolant feed pipe for heating circuit

3 Coolant return line

E Expansion reservoir

F Radiator

G Exhaust gas recirculation cooler

A Thermostat

B Coolant pump

C Engine

D Heating system heat exchanger

General

Components of the engine suffer high thermal loading from the combustion taking place in the engine.

Apart from actually leading away excess heat a cooling system must also fulfill the following tasks:

 Rapid reaching of the engine operating temperature

 Holding the engine operating temperature as constant as possible under all driving conditions

 Protecting the engine lubricant from overheating and decomposition

 Protecting fresh air from excessive warming in order to allow high efficiency of the engine

Function

The engine cooling is subdivided into a small and a large coolant circuit.

For a cold engine the coolant flows via the small coolant circuit from the coolant pump through the engine to the thermostat and back to the coolant pump.

If the engine has reached its operating temperature, the thermostat opens the large coolant circuit. This subdivides immediately after the thermostat into the cooling circuit and the heating circuit.

In the cooling circuit, the coolant flows via the coolant feed pipe for the cooling circuit to the radiator and from there via the coolant return line back to the coolant pump.

In the heating circuit, the coolant flows via the coolant feed pipe for the heating circuit to the exhaust gas recirculation cooler and the heater heat exchanger to the expansion reservoir.

The coolant flows via the coolant return line from the expansion reservoir back to the coolant pump.

 If the coolant was partially or fully drained off the coolant circuit must be bled. Filling and bleeding of the coolant circuit may only be undertaken on a cold engine.