DEFINITION: Either of the following conditions indicate a probable engine overheat condition.

1. Inspect and fill the cooling system, as necessary. Refer to Cooling System Draining and Filling .
2. Inspect the cooling system for leaks, as necessary.
3. Repair the cooling system leaks, as necessary.

Has the inspection/repair been performed?

Go to Step 2

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1. Start the engine and allow the engine to run at approximately 1,200 RPM.
2. Use the Scan Tool in order to verify the overheat condition.

Does the Scan Tool verify the engine overheat condition?

Go to Step 3

Go to Diagnostic System Check - Vehicle

1. Verify that the cooling fans are operating properly.
2. Repair the cooling fan system, as necessary.

Does the engine still overheat?

Go to Step 4

System OK

Perform the following inspections:

Does the engine still overheat?

Go to Step 5

System OK

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

Is the thermostat operating properly?

Go to Step 7

Go to Step 6

Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .

Does the engine still overheat?

Go to Step 7

System OK

Important: Excessive coolant freeze point protection MAY cause the coolant to boil at low temperatures.

1. Inspect for the proper coolant concentration (mixture). Correct the coolant concentration as necessary.
2. Remove the radiator cap.
3. Start the engine and inspect for a constant flow of air bubbles in the engine coolant.

Is there a constant flow of air bubbles in the engine coolant?

Go to Step 8

Go to Step 9

The probable cause of the engine overheat is combustion chamber gasses leaking into the cooling system. This condition is usually caused by the following:

Verify this condition by inspecting the spark plug electrodes and porcelain surrounding the spark plug electrode for signs of coolant. Replace and/or repair the engine internal component(s), as necessary, in order to repair the engine internal coolant leak.

Does the engine still overheat?

Go to Step 1

System OK

The engine overheat may be caused by a cooling system blockage. Flush the cooling system. Refer to Flushing .

Does the engine still overheat?

Go to Step 10

System OK

Important: It is unlikely that the water pump is the cause of the overheat condition.

If NONE of the cooling system passages are restricted, replace the coolant pump. Refer to Water Pump Replacement .

Does the engine still overheat?

Go to Step 1

System OK

DEFINITION: The engine temperature lamp comes on and stays on, or temperature gage shows hot, or coolant overflows from the surge tank onto the ground while the engine is running.

Special Tools

J-26568 Coolant and Battery Fluid Tester

Check the condenser, radiator, and auxiliary coolers for any obstructions or bent fins that would prevent air flow through the radiator.

Is there any airflow obstruction or bent fins?

Go to Step 2

Go to Step 3

1. Remove any debris that may cause an air flow obstruction.
2. Remove or relocate aftermarket add-on components that block air flow to the radiator.

Does the engine still overheat?

Go to Step 3

System OK

Check for loose, missing, or damaged radiator air seals or deflectors.

Are there any loose, missing, or damaged radiator air seals or deflectors?

Go to Step 4

Go to Step 5

Repair or replace any loose, missing, or damaged radiator air seals or deflectors.

Does the engine still overheat?

Go to Step 5

System OK

Check for an inoperative cooling fan. Refer to Cooling Fan Inoperative.

Is the thermostat operating properly?

Go to Step 6

Go to Step 7

Repair or replace the cooling fan(s) as necessary. Refer to Engine Coolant Fan Motor Replacement.

Does the engine still overheat?

Go to Step 7

System OK

Check for a loss of coolant. Refer to Loss of Coolant

Does the engine still overheat?

Go to Step 8

System OK

Check for kinked or pinched cooling hoses.

Are any cooling hoses kinked or pinched?

Go to Step 9

Go to Step 10

1. Relieve any kinks by rerouting the hoses.
2. Replace the hoses, if necessary.

Does the engine still overheat?

Go to Step 10

System OK

Using J-26568 Coolant and Battery Fluid Tester , check the coolant concentration.

Does the coolant concentration test correctly?

Go to Step 12

Go to Step 11

Replace the coolant, if necessary. Refer to Loss of Coolant

Does the engine still overheat?

Go to Step 12

System OK

Check for any blocked cooling system passages.

Are there blocked cooling system passages?

Go to Step 13

Go to Step 14

Remove any obstructions by flushing the cooling system. Refer to Flushing

Does the engine still overheat?

Go to Step 14

Go to Step 19

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

Does the engine still overheat?

Go to Step 15

System OK

Check for a faulty thermostat. Refer to Thermostat Diagnosis

Does the engine still overheat?

Go to Step 16

System OK

Replace the radiator. Refer to Radiator Replacement

Does the engine still overheat?

Go to Step 17

System OK

Check for a faulty water pump. The impeller blades may be eroded or broken.

Is the water pump faulty?

Go to Step 18

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Replace the water pump. Refer to Water Pump Replacement

Did you complete the repair?

Go to Step 19

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Operate the system to verify the repair.

Did you correct the condition?

System OK

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