1. Pressure test the cooling system and the surge tank cap for leaks.

•	Refer to Cooling System Leak Testing .

•	Refer to Radiator Cap .

2. Repair any leaks before you proceed. These engines use a 91°C (195°F) thermostat. The ambient temperatures should be between 13-38°C (55-100°F).
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 coolant temperature.
5. Check the engine coolant temperature at idle with the tech 1 .

Is the engine coolant temperature between the specified values?

85-96°C (185-205°F)?

System OK

Go to Step 2

Is the engine coolant temperature below the specified value?

85°C (185°F)

Go to Step 3

Go to Step 4

The thermostat is opening early, or the thermostat seal is leaking.

Replace the thermostat or the seal. Refer to Engine Coolant Thermostat Replacement .

Is the repair complete?

--

System OK

--

Is the engine coolant temperature over the specified value?

96°C (205°F)

Go to Step 5

--

Is the radiator inlet hot?

--

Go to Step 6

Go to Step 7

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

There may be air in the system.

1. Add coolant to the surge tank if the coolant level is low. Refer to Cooling System Maintenance Recommendations .
2. Recheck the radiator inlet hose.

Is the inlet hose hot?

--

Go to Step 6

Go to Step 8

Inspect for blockage in the following areas:

Is there a blockage?

--

Go to Step 9

Go to Step 10

1. Repair the blockage.
2. Recheck the coolant temperature with the tech 1 .

Is the repair complete?

--

System OK

--

1. Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .
2. Recheck the coolant temperature with the tech 1 .

Is the repair complete?

--

System OK

--

Inspect for blockage in the radiator.

Is there any blockage?

--

Go to Step 9

Go to Step 10

1. Accelerate the engine several times in order to remove any air from the system.
2. Inspect for blockage in the heater circuit. Refer to Heater Diagnosis in Air Conditioning.
3. Inspect for any pinched or buckled hoses.

Is there any blockage?

--

Go to Step 9

Go to Step 13

Refer to heater diagnosis in Air Conditioning.

Is the repair complete?

System OK

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