GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Classic 🢒 Engine 🢒 Engine Cooling 🢒 Thermostat Diagnosis

Step

Action

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) thermostat. Six cylinder engines use a 91°C (195°F) thermostat.

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 20-21°C (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

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5

Test the thermostat for the following conditions:

    • Opening early
    • Seal is leaking

Are either of these conditions present?

Go to Step 6

System OK

6

Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .

Is the repair complete?

System OK

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7

Is the radiator inlet hot?

Go to Step 8

Go to Step 14

8
  1. Turn ON the heater.
  2. 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
  1. Repair the blockage.
  2. Reinspect the radiator with the Scan Tool .

Is the repair complete?

System OK

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11
  1. Replace thermostat. Refer to Engine Coolant Thermostat Replacement .
  2. 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 Heating Performance Diagnostic

13
  1. Repair the blockage.
  2. Reinspect the radiator with the Scan Tool .

Is the repair complete?

System OK

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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
  1. Repair the blockage.
  2. Reinspect the radiator with the Scan Tool .

Is the repair complete?

System OK

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17
  1. Repair the thermostat.
  2. Reinspect the radiator with the Scan Tool .

Is the repair complete?

System OK

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