General information and precautions (Audi A4 B7)

The engine cooling system operates according to the following algorithm. While the engine is not warmed up, the coolant (coolant) is pumped by the water pump only in the cylinder head and block, as well as in the heat exchanger of the climate control system heater (see illustration 1.1). When the coolant temperature rises to a certain level, the thermostat opens a large cooling circuit and the coolant circulates additionally through the radiator, cooling itself with the air passing through it. When the coolant temperature reaches an even higher value, the electric fan of the cooling system turns on, which creates an additional air flow through the radiator fins for more intensive heat removal from it.







On 4-cylinder petrol models the thermostat is controlled by the ECM based on the data received from the MAP sensor. On other engines a traditional thermostat is used, which opens when a certain temperature of the coolant directly in contact with the thermostat is reached.

Some engines use two coolant temperature sensors: one (ECT) detects the coolant temperature in the engine cooling system circuit, which is used to calculate the amount of fuel injected and the set idle speed value; another (radiator outlet temperature sensor) determines the coolant temperature after the radiator, which is used to turn on the fan.

Precautionary measures

Before working in the engine compartment, especially in the radiator fan area, be sure to disconnect the negative battery cable and the fan wiring connector, as it may turn on due to thermal conductivity even when the ignition is off.



Do not open the coolant expansion tank or radiator cap until the engine has completely cooled down to avoid being burned by hot liquid or its steam.

If you need to open the expansion tank cap when the engine is hot, wrap it with a rag. Remove the cap slowly, gradually reducing the steam pressure.

Descriptions of checking and adjusting the coolant level, replacing the coolant, and some cooling system checks are provided in Sections 4 and 5 Chapters 1.