Cooling system (Audi 100 C3)

Overheat

• Insufficient level of refrigerant in the system ("Weekly checks").
• Thermostat is faulty (Section 2).
• The radiator is clogged (Section 2).
• The electric cooling fan or thermal switch is faulty
• Defective pressure cap on the radiator (Section 2).
• Inaccurate temperature sensor (Section 2).
• Air lock in the cooling system.

Hypothermia

• Thermostat is faulty (Section 2).
• Inaccurate temperature sensor (Section 2).

External refrigerant leak

• Deteriorated or damaged hoses or hose clamps.
• The radiator or heater is damaged (Section 2).
• Defective pressure cap (Section 2).
• The water pump insulation is damaged (Section 2).
• Boiling due to overheating (Section 2).
• Leak from under the plug (Section 1).

Internal refrigerant leak

• Leaking cylinder head gasket (Section 1).
• The cylinder head or cylinder bore is cracked (Section 1).

Corrosion

• Irregular draining of fluid and flushing of the system.
• Incorrect refrigerant mixture or incorrect refrigerant type.

[This publication is borrowed from the resource «AudiManual.ru»]