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

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

Common leak sources:

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

Diagnostic steps:

• Visual inspection of all coolant components
• Pressure test the cooling system
• Use UV dye to locate small leaks

Repair procedures:

• Expansion tank replacement:
  - Drain coolant
  - Remove hoses and electrical connections
  - Replace tank (BMW part number: 17117573781)
• Radiator replacement:
  - Remove fan shroud and electric fan
  - Disconnect hoses and remove radiator
  - Install new radiator and refill system
• Water pump replacement:
  - Remove serpentine belt
  - Remove water pump bolts and replace pump

Note: Always use BMW-approved coolant and properly bleed the cooling system after repairs.