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Thermostat Diagnosis (1.6L Diesel LH7)

Step Action Values Yes No
1
  1. Pressure test the cooling system and the cap for leaks.
  2. Repair any leaks before proceeding. The thermostat start to open at 96°C (205°F) and fully open at 109°C (228°F). 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 20°C-21°C (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 96 - 109°C (205-228°F)?		 13 - 38°C (55 - 100°F) System OK Go to Step 2 
2 Is the ECT below 96°C (205°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. Refer to Engine Coolant Thermostat Replacement .
Is the repair complete?		 - System OK -
4 Is the ECT over 109°C (228°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 .
  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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