Audi A4

since 1994 release

Manual of the car


Audi A4
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ System of an exhaust
- Cooling system
   So there is a cooling
   Check of level of cooling liquid
   Antifreeze check
   Check of the cooling system on tightness
   Radiator
   Locking cover of the cooling system
   Thermostat
   The help at malfunctions
   Water pump
   Maple belt of the water pump
   Various models of fans
   Viscous fan
   The radiator fan with the electric drive
   Violations in operation of the fan of a radiator
   The help at malfunctions
+ Fuel tank and fuel pump
+ Air filter and channels of absorption
+ System of injection
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
+ Electrotechnical equipment
+ System of ignition
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ Body details
+ Salon
Search of malfunctions
Technical characteristics

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So there is a cooling

The water pump at the working engine constantly drives cooling liquid via numerous channels of cooling of the engine and thus takes away the warmth arising due to combustion in cylinders. The pump accelerates a stream of cooling liquid by means of a bladed wheel which is at it on a reverse side.

The drive of the water pump in the four-cylinder engine is provided with a maple belt, in the six-cylinder engine – a gear belt. In what way cooling liquid flows on uncountable hoses and channels, depends on its temperature at present.

  • If the engine is not warmed up yet, then cooling liquid moves on "a small contour" which goes via the engine and the heat exchanger of heating. Depending on engine model the oil heater is in addition connected to a small contour of circulation of cooling liquid.
  • At a temperature over 87 °C the thermostat opens "a big contour" in which the radiator is connected.
  • If temperature continues to increase further so that even in an environment of a radiator reaches 82 °C, viscous coupling of the fan of a radiator switches to the rigid direct drive – the fan rotates too.
  • In cars with the electric drive of the fan of a radiator (climatic installation) the fan is connected if in a radiator temperature reaches about 92 °C.

Cooling system of elevated pressure

At a working temperature in the cooling system there is an elevated pressure in 1,2–1,5 bars that considerably increases water boiling temperature – over 100 °C under usual conditions. Thus the reserve is created, the engine can reach working temperatures over 100 °C, and at the same time not "dangers of boiling of liquid" in the cooling system.

The correct pressure in the cooling system is provided with a locking cover of a broad tank in which there are a safety valve of elevated pressure (about 1,2-1,5 bars) and the safety valve of the lowered pressure (0,06–0,1 bars).

The valve of the lowered pressure lets in an air stream if temperature of cooling liquid goes down and, therefore, occupies smaller volume.

In a locking cover (1) of the cooling system, on a jellied branch pipe (2) of a broad tank valves of the increased and lowered pressure settle down. Sideways on a transparent tank there is a marking of level of liquid (3 and 4).