GM Service Manual Online
For 1990-2009 cars only

Step

Action

Values

Yes

No

1

Inspect for a loss of system pressure and/or coolant.

Is there a loss of system pressure and/or coolant?

--

Go to Step 2

Go to Step 3

2

Inspect and repair any faulty hose connections or radiator cap. Fill the system to the proper level, then retest.

Does the engine still overheat beyond the specified value?

125°C (257°F)

Go to Step 3

System OK

3

Inspect the coolant concentration for low temperature protection below the specified value.

Is the proper low temperature protection present?

-37°C (-34°F)

Go to Step  5

Go to Step 4

4

Replace the coolant. Refer to Cooling System Draining and Filling .

Does the engine still overheat?

--

Go to Step 5

System OK

5

Inspect the drive belt for excessive wear or low tension.

Is the drive belt worn or is the tension too low?

--

Go to Step 6

Go to Step 7

6

Replace the drive belt. Refer to Drive Belt Replacement .

Does the engine still overheat?

--

Go to Step 7

System OK

7

Inspect the radiator fins for obstruction.

Are the radiator fins obstructed?

--

Go to Step 8

Go to Step 9

8

Inspect and clean the radiator. Refer to Radiator Cleaning .

Does the engine still overheat?

--

Go to Step 9

System OK

9

Inspect the water pump for physical damage.

Is the water pump damaged or inoperative?

--

Go to Step 10

Go to Step 11

10

Replace the water pump. Refer to Water Pump Replacement .

Does the engine still overheat?

--

Go to Step 11

System OK

11

Inspect the cooling system passages for obstruction.

Is the cooling system passage blocked?

--

Go to Step 12

Go to Step 13

12

Inspect and flush the system. Refer to Flushing .

Does the engine still overheat?

--

Go to Step 13

System OK

13

Inspect the electro-viscous fan.

Is the electro-viscous fan inoperative?

--

Go to Step 14

Go to Step 15

14

Replace the electro-viscous fan.

Does the engine still overheat?

--

Go to Step 15

System OK

15

Inspect for a stuck thermostat. Refer to Thermostat Diagnosis .

Is the thermostat stuck in the closed position?

--

Go to Step 16

Go to Step 17

16

Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .

Does the engine still overheat?

--

Go to Step 17

System OK

17

The following factors may cause the engine to overheat:

    • A heavy vehicle payload
    • The A/C system
    • Excess engine oil
    • Restricted air flow through the radiator
    • Extreme air temperature

Correct or repair as necessary.

Does the engine still overheat?

--

--

System OK