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Heater Core - Plugged

WARNING: The heater core inlet hose will become too hot to handle if the system is working correctly.
  1. Check to see that the engine coolant is at the correct level.
  2. Start the engine and turn on the heater.
  3. When the engine coolant reaches operating temperature, feel the heater core inlet and outlet hoses to see if they are hot.
  4. If the outlet only is not hot:
    • the heater core may have an air pocket.
    • the heater core may be plugged.
  5. If the inlet only is not hot:
    • the thermostat may not be working correctly.
    • the coolant control valve may not be working correctly.
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