Troubleshooting the cooling system (BMW 3 Series E46)

Overheat

• Insufficient amount of coolant in the system ("Weekly check").
• Thermostat malfunction (chapter 3).
• Clogged radiator or radiator grille (chapter 3).
• Malfunction of the electric radiator cooling fan or viscous coupling (chapter 3).
• Coolant temperature sensor malfunction (chapter 3).
• Air lock in the cooling system (chapter 3).
• The radiator cap is faulty (chapter 3).

Hypothermia

• Thermostat malfunction (chapter 3).
• Coolant temperature sensor malfunction (chapter 3).
• Viscous coupling failure (chapter 3).

External coolant leak

• Damage to hoses or clamps (chapter 1).
• Leak through the radiator or heater heat exchanger (chapter 3).
• The radiator cap is faulty (chapter 3).
• Leak through the internal seal of the coolant pump (chapter 3).
• Leak through the seal of the joint between the pump and the cylinder block of the cooling system (chapter 3).
• Liquid boiling due to overheating (chapter 3).
• Leak through the radiator cap (chapter 3).

Internal coolant leak

• Cylinder head gasket leak (chapter 2).
• Crack in the cylinder head or cylinder liner (chapter 2).

Corrosion

• Rare replacement of fluid and flushing of the cooling system (chapter 1).
• Unregulated composition of coolant or inappropriate type of antifreeze ("Weekly checks").