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Thermostat Diagnosis (1.8L LUW and LWE)

Step Action Values Yes No
The procedure is ONLY valid for a mechanical opening without an electrical heating.
1
  1. Pressure test the cooling system and the cap for leaks.
  2. Repair any leaks before proceeding. These engines use a 105°C (221°F) thermostat. The ambient temperatures should be within the specified range given.
  3. Set the HVAC controls in the OFF position.
  4. Run the cold engine at idle (68-70°F) for 15-20 minutes before checking the engine temperature.
  5. Check the engine coolant temperature at idle with the scan tool.
Is the engine coolant temperature (ECT) between 105-120°C (221-248°F)?		 13-38°C (55-100°F) System OK Go to Step 2 
2 Is the ECT below 105°C (221°F)? - Go to Step 3  Go to Step 4 
3 The thermostat is opening early or the thermostat seal is leaking.
Replace the thermostat and the thermostat seal.
Is the repair complete?		 - System OK -
4 Is the ECT over 120°C (248°F)? - Go to Step 5  -
5 Is the radiator inlet hot? - Go to Step 6  Go to Step 7 
6
  1. Turn ON the heater.
  2. Check if hot air is coming from the heater outlets.
Is the air hot?		 - Go to Step 11  Go to Step 12 
7 There may be air in the system.
  1. Add coolant to the surge tank if the coolant level is low. Refer to Cooling System Draining and Filling (GE-47716 Fill)  and Cooling System Draining and Filling (Static Fill) .
  2. Recheck the radiator inlet hose.

Is the inlet hose hot?		 - Go to Step 6  Go to Step 8 
8 Inspect for blockage in the following areas:
  • The cylinder head
  • The radiator
  • The radiator hoses

Is there a blockage?		 - Go to Step 9  Go to Step 10 
9
  1. Repair the blockage.
  2. Recheck the coolant temperature with the scan tool.
Is the repair complete?		 - System OK -
10
  1. Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .
  2. Recheck the coolant temperature with the scan tool.
Is the repair complete?		 - System OK -
11 Inspect for blockage in the radiator.
Is there any blockage?		 - Go to Step 9  Go to Step 10 
12
  1. Accelerate the engine several times in order to remove any air from the system.
  2. Inspect for blockage in the heater circuit.
  3. Inspect for any pinched or buckled hoses.
Is there any blockage?		 - Go to Step 9  Go to Step 13 
13 Is the repair complete? - System OK -
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