How to fix coolant leak in BMW E46 318i (N42B18)

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How to fix coolant leak in BMW E46 318i (N42B18)

Common leak sources:

• Expansion tank
• Radiator
• Water pump
• Thermostat housing
• Hoses and connections

Diagnostic steps:

• Perform a visual inspection of all coolant components
• Pressure test the cooling system (use BMW special tool 17 0 000 or equivalent)
• Use UV dye to locate small leaks

Fixing common issues:

• Expansion tank replacement:
  - Drain coolant
  - Remove upper and lower hoses
  - Unclip the tank from mounting bracket
  - Install new tank (BMW part number: 17137787039)
• Radiator replacement:
  - Drain coolant
  - Remove fan shroud and electric fan
  - Disconnect upper and lower hoses
  - Remove radiator mounting bolts
  - Install new radiator (e.g., Behr 376745761)
• Water pump replacement:
  - Remove serpentine belt
  - Remove fan and fan clutch
  - Remove water pump bolts
  - Install new pump with gasket (e.g., Graf PA1006)

Always refill with BMW-approved coolant and bleed the system properly.