my BMW 3 Series E90/E91 (2005-2012) is leaking coolant, what's the problem?

Solution

1. Preparation

• Gather tools and parts.
• Ensure the engine is cool and disconnect the battery.
• Place a drain pan under the engine to catch any spilled coolant.

2. Inspect and Replace Reservoir

• Remove the coolant reservoir cap.
• If the reservoir is cracked:
  • Disconnect the hoses attached to the reservoir.
  • Unbolt the reservoir from its mounting brackets.
  • Replace with a new coolant reservoir.
  • Reattach hoses and secure the reservoir.

3. Check and Replace Hoses

• Inspect both upper and lower radiator hoses:
  • If any hoses are cracked or bulging:
    • Loosen the hose clamps and remove the damaged hose.
    • Install new hoses, ensuring they are the correct length.
    • Tighten hose clamps to secure the hoses.

4. Replace Water Pump

• If the water pump is leaking:
  • Drain the coolant and remove the serpentine belt.
  • Unbolt the water pump from the engine block.
  • Clean the mounting surface and install a new water pump with a new gasket.
  • Refill the cooling system with the appropriate coolant.

5. Thermostat Housing Replacement

• If the thermostat housing is leaking:
  • Remove the coolant hoses connected to the thermostat housing.
  • Unbolt the housing from the engine.
  • Install a new thermostat housing with a new gasket.
  • Reconnect hoses and refill coolant.