Audi 80/Avant (B4)

since 1991-1995 release

Repair and operation of the car

Audi 80/Avant
+ Technical specification
+ Engines
+ System of production of the fulfilled gases
- Cooling system
   Check of level of cooling liquid
   Frost resistance check
   Check of the cooling system on tightness
   Carving cover of a broad tank
   List of malfunctions
   Water pump
   Maple belt of the water pump
   Cooling system fan
   Malfunctions of the fan of the cooling system
   List of malfunctions
+ Fuel tank and fuel pump
+ Air filter and airintaking channels
+ System of injection
+ Coupling
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
+ Anti-blocking system of brakes
+ Wheels and tires
+ Body electrical system
+ System of ignition
+ Lighting
+ Signalling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ body Elements
+ Search of malfunctions
+ Specifications

Carving cover of a broad tank

In the conditions of an elevated pressure of the cooling system an important role is played by a carving cover of a broad tank:

  • At the closed cover its sealing surface strong nestles on edge of an opening of a broad tank and if the safety valve is closed, losses of pressure are not present.
  • If when heating pressure in the cooling system exceeds 1,2 – 1,5 bars – the safety valve opens and a quantity of water vapor jumps out. Pressure is leveled.
  • When cooling liquid again decreases in volume, and in the cooling system the lowered pressure is formed. For an equilibration of this lowered pressure in a cover there is the second valve. It opens with the lowered pressure of 0,06 - 1,0 bars so can be a part of the system external air.

Check of the safety valve

Who does not want to suffer with check, in a suspicious case simply has to replace rather inexpensive carving cover.

The workshop checks it by means of the manometer:

With a pressure of 1,2 - 1,5 bars the valve has to open.

Check of the vacuum valve

It is only possible to define approximately, whether this valve works.


  1. At the removed carving cover strongly to squeeze a thick tube of the cooling system.
  2. To put on and tighten a cover.
  3. To release a hose.
  4. If the squeezed hose again is rounded, the valve, most likely, as it should be.
  5. If cooling system tubes before the first start look in the morning flat and squeezed, the vacuum valve is for certain faulty.