GM Service Manual Online
For 1990-2009 cars only

Engine Overheating General

Step

Action

Value(s)

Yes

No

1

Check for a loss of coolant.

Is there a loss of coolant?

--

Go to Step 2

Go to Step 3

2

  1. Refer to Coolant Heater Diagnosis .
  2. Fill the system to the specified level, then retest.

Does the engine overheat?

--

Go to Step 3

System OK

3

Check for a faulty engine coolant temperature (ECT) sensor.

Is the sensor operating properly?

--

Go to Step 4

Go to Step 6

4

Check for a loss of system pressure, refer to Cooling System Leak Testing .

Is there a loss of system pressure?

--

Go to Step 6

Go to Step 5

5

Check for a low coolant concentration level, refer to Coolant Concentration Testing .

Is the coolant concentration low?

--

Go to Step 6

Go to Step 7

6

Repair or install new parts as necessary, then retest.

Does the engine overheat?

--

Go to Step 7

System OK

7

Check for incorrect drive belt tension, refer to Drive Belt Tensioner Diagnosis in Engine Mechanical.

Is the belt tension correct?

--

Go to Step 8

Go to Step 6

8

Check for retarded ignition timing, refer to Engine Mechanical.

Is the timing retarded?

--

Go to Step 6

Go to Step 9

9

Check for an obstructed radiator air flow or bent fins, refer to Cooling System Description .

Is the radiator air flow obstructed?

--

Go to Step 6

Go to Step 10

10

Check for a pinched or leaking coolant recovery reservoir hose, refer to Coolant Recovery System Description .

Is the reservoir hose OK?

--

Go to Step 11

Go to Step 6

11

Check for an inoperative cooling fan, refer to Coolant Heater Diagnosis .

Is the fan operating properly?

--

Go to Step 12

Go to Step 6

12

Check the coolant thermostat, refer to Engine Fails To Reach Normal Operating Temperature .

Is the thermostat stuck in the CLOSED position?

--

Go to Step 6

Go to Step 13

13

Check for a faulty coolant pump, refer to Coolant Heater Diagnosis .

Is the coolant pump operating properly?

--

Go to Step 14

Go to Step 6

14

Check for a loose, damaged or missing air deflector.

Is this system OK?

--

Go to Step 15

Go to Step 6

15

Check the radiator cooling capacity.

Is the radiator the specified one for the vehicle accessory package (including aftermarket items)?

--

Go to Step 16

Go to Step 6

16

Does the overheating occur only when pulling a trailer?

Is the trailer weight, plus the vehicle weight less than the GCWR for the vehicle?

--

Go to Step 17

Go to Step 15

17

Does the overheating occur with prolonged idling (especially with the AC ON)?

--

Go to Step 18

Go to Step 1

18

Instruct the owner about driving techniques which will minimize this problem.

Is the driver informed?

--

System OK

Engine Overheating Radiator Diagnosis

Engine Overheats

Step

Action

Value(s)

Yes

No

1

Check for an obstructed air flow through the radiator.

Is the air flow path clear?

--

Go to Step 3

Go to Step 2

2

Remove or relocate added on parts that may block the air flow through the radiator.

Is the air flow path clear now?

--

System OK

--

3

Check for plugged radiator fins.

Are the radiator fins plugged?

--

Go to Step 4

Go to Step 5

4

Remove any debris (bugs, leaves, etc.) from the radiator fins.

Are the fins clear now?

--

System OK

--

5

Check the radiator for leaks, refer to Cooling System Leak Testing

Is the radiator leaking?

--

Go to Step 6

Go to Step 7

6

Repair or replace the radiator as necessary.

Is the repair complete?

--

System OK

--

7

Check the radiator for bent fins.

Are the fins bent?

--

Go to Step 8

--

8

Repair the bent fins or replace the radiator core.

Is the repair complete?

--

System OK

--