GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

The engine may overheat due to an intermittent operation of the thermostat.

Step

Action

Values

Yes

No

DEFINITION: Engine temperature lamp comes ON and stays ON, or the temperature gage shows hot, or coolant overflows from the coolant recovery reservoir onto the ground while the engine is running.

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Inspect the coolant recovery reservoir for low coolant.

Is there a loss of coolant?

--

Go to Loss of Coolant

Go to Step 3

3

Important: Do not allow the engine temperature to exceed the specified value.

Start the engine and allow to reach normal operating temperature.

Does the engine begin to exceed the specified value?

107°C (225°F)

Go to Step 4

Go to Diagnostic Aids

4

Inspect for loose, damaged, and/or missing of the following:

    • The A/C condenser seals
    • The front air deflector
    • The side seals

Repair the system as necessary.

Does the engine still overheat?

--

Go to Step 5

Go to Step 17

5

Using the J 23688 Coolant and Battery Fluid Tester, test for insufficient coolant concentration.

Is the coolant protection greater than the specified value?

-37°C (-34°F)

Go to Step 6

Go to Step 7

6

Correct the coolant concentration as necessary.

Does the engine still overheat?

--

Go to Step 7

Go to Step 17

7

Inspect for obstructed radiator air flow or bent radiator fins.

Is the radiator air flow obstructed?

--

Go to Step 8

Go to Step 9

8

Clean the radiator. Refer to Radiator Cleaning .

Does the engine still overheat?

--

Go to Step 9

Go to Step 17

9

Inspect the drive belt tensioner. Refer to Drive Belt Tensioner Diagnosis or Drive Belt Tensioner Diagnosis .

Is the drive belt tensioner working properly and is the tension correct?

--

Go to Step 11

Go to Step 10

10

Replace the drive belt tensioner. Refer to Drive Belt Tensioner Replacement or Drive Belt Tensioner Replacement .

Does the engine still overheat?

--

Go to Step 11

Go to Step 17

11

Inspect the thermostat for proper operation. Refer to Thermostat Diagnosis .

Does the thermostat operate properly?

--

Go to Step 13

Go to Step 12

12

Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .

Does the engine still overheat?

--

Go to Step 13

Go to Step 17

13

Inspect for an inoperative fan clutch. Refer to Fan Clutch Diagnosis .

Does the engine still overheat?

--

Go to Step 14

Go to Step 17

14

Inspect for blocked cooling system passages.

Are the cooling system passages blocked?

--

Go to Step 15

Go to Step 16

15

Replace the radiator. Refer to Radiator Replacement .

Does the engine still overheat?

--

Go to Step 16

Go to Step 17

16

Replace the engine water pump. Refer to Water Pump Replacement .

Did you complete the repair?

--

Go to Step 17

--

17

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2