For 1990-2009 cars

Pressure check the cooling system and the cap for leaks. Repair any leaks before proceeding with the diagnosis. Four cylinder engines use an 82°C (185°F) T/STAT. Six cylinder engines use a 91°C (195°F) T/STAT.

Ambient temperatures should be between 13°-38°C (55°-100°F). Place the HVAC controls in the OFF position. Run a cold engine at idle (68°-70°F) for 15-20 minutes before checking the engine temperature.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Pressure check the cooling system and the cap for leaks. Repair any leaks before proceeding with the diagnosis. Four cylinder engines use an 82°C (185°F) T/STAT. Six cylinder engines use a 91°C (195°F) T/STAT. Ambient temperatures should be between 13°-38°C (55°-100°F). Place the HVAC controls in the OFF position. Run a cold engine at idle (68°-70°F) for 15-20 minutes before checking the engine temperature.

Is the repair complete?

--

Go to Step 2

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2 | Verify the engine coolant temperature with a Scan Tool at idle. Is the engine temperature below 85°C (185°F)? | -- | Go to Step 5 | Go to Step 3
3 | Verify the engine coolant temperature with a Scan Tool at idle. Is the engine coolant temperature between 85-96°C (185-205°F)? | -- | System OK | Go to Step 4
4 | Verify the engine coolant temperature with a Scan Tool at idle. Is the engine coolant temperature over 96°C (205°F)? | -- | Go to Step 7 | --
5 | Test the T/STAT for the following conditions:

1. The T/STAT is opening early
2. The T/STAT seal is leaking

Are either of these conditions present?

--

Go to Step 6

System OK

6 | Replace the T/STAT and replace the T/STAT seal. Refer to Engine Coolant Thermostat Replacement . Is the repair complete? | -- | System OK | --
7 | Is the radiator inlet hot? | -- | Go to Step 8 | Go to Step 14
8 | Turn on the heater. Check for hot air at the heater outlets. Is the air hot? | -- | Go to Step 9 | Go to Step 12
9 | Inspect for blockage in the radiator. Did you find any blockage? | -- | Go to Step 10 | Go to Step 11
10 | Repair the blockage. Reinspect the radiator with the Scan Tool . Is the repair complete? | -- | System OK | --
11 | Replace T/STAT. Refer to Engine Coolant Thermostat Replacement . Reinspect the radiator with the Scan Tool . Is the repair complete? | -- | System OK | --
12 |

1. Rev the engine several times to remove any air.
2. Inspect for blockage in the heater circuit.
3. Inspect for pinched or buckled hoses.

Did you find any blockage?

--

Go to Step 13

Go to Radiator Hose Replacement in HVAC Systems with AC - Manual

13 | Repair the blockage. Reinspect the radiator with the Scan Tool . Is the repair complete? | -- | System OK | --
14 | Air may be in the system.

1. Add coolant to surge tank if low.
2. Reinspect the radiator inlet hose.

Is the hose hot?

--

Go to Step 8

Go to Step 15

15 | Inspect for blockage in the following locations:

• | The cylinder head

• | The radiator

• | The radiator hoses

• | The radiator nipples

Did you find any blockage?

--

Go to Step 16

Go to Step 17

16 | Repair the blockage. Reinspect the radiator with the Scan Tool . | -- | System OK | --
17 | Replace T/STAT. Refer to Engine Coolant Thermostat Replacement . Reinspect the radiator with the Scan Tool . Is the repair complete? | -- | System OK | --