my Volkswagen Passat B8 (2015-2022) is losing coolant but no visible leaks

Solution

1. Preparation

• Tools Required: OBD-II scanner, pressure tester, socket set, torque wrench, coolant, oil filter wrench.
• Safety Warnings: Allow the engine to cool completely before starting work on the cooling system. Wear gloves and safety goggles.

2. Perform Pressure Test

• Sub-steps:
  1. Remove the coolant reservoir cap.
  2. Attach the pressure tester to the radiator or reservoir.
  3. Pump the tester to the specified pressure (usually around 15 psi).
  4. Observe for any pressure drop which indicates a leak.
  5. Check hoses and connections for any signs of coolant seeping out.

3. Inspect Oil and Engine Components

• Sub-steps:
  1. Remove the oil filler cap and inspect for milky residue.
  2. If present, this indicates coolant contamination and may require replacing the head gasket.
  3. Check the radiator cap for any signs of brittleness or damage.

4. Repair Identified Issues

• Sub-steps:
  1. If leaks are found, replace damaged hoses or components.
  2. If the head gasket is confirmed faulty, follow these steps:
     • Drain the coolant and oil.
     • Remove the necessary engine components to access the cylinder head.
     • Replace the head gasket with a new one, ensuring to clean surfaces thoroughly.
     • Reassemble components, and torque to manufacturer specifications (usually 20-30 Nm for cylinder head bolts).
     • Refill with coolant and oil.