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. Refer to Cooling System Leak Testing .
3. Repair the cooling system leaks as necessary.

Has the inspection/repair been performed?

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Go to Step 2

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1. Start the engine and allow the engine to run at approximately 1200 RPM.
2. Use the Scan Tool in order to verify the overheat condition.

Does the Scan Tool verify the engine overheat condition?

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Go to Step 3

Go to Engine Coolant Temperature Gauge Inaccurate or Inoperative or Engine Coolant Temperature Indicator Inoperative in Instrument Panel, Gauges and Console.

1. Verify that the cooling fans are operating properly. Refer to Electric Cooling Fan Diagnosis in Engine Controls - 3.4L.
2. Repair the cooling fan system as necessary.

Does the engine still overheat?

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Go to Step 4

System OK

Perform the following inspections:

Does the engine still overheat?

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Go to Step 5

System OK

Caution: As long as there is pressure in the cooling system, the temperature can be considerably higher than the boiling temperature of the solution in the radiator without causing the solution to boil. Removal of the pressure cap while the engine is hot and pressure is high will cause the solution to boil instantaneously -- possibly with explosive force -- spewing the solution over the engine, fenders and the person removing the cap.

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

Is the thermostat operating properly?

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Go to Step 7

Go to Step 6

Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .

Does the engine still overheat?

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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). Refer to Coolant Concentration Testing . Correct the coolant concentration as necessary.
2. Remove the radiator cap.
3. Start the engine and inspect for a steady and constant flow of air bubbles in the engine coolant.

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

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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 a faulty cylinder head gasket. However, a faulty cylinder head or a faulty engine block may also be the cause of the engine overheat condition. This condition may be verified by spark plug electrodes or the porcelain surrounding the spark plug electrodes that exhibit signs of coolant. Replace the engine internal component(s) as necessary in order to repair the engine internal coolant leak.

Does the engine still overheat?

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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?

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Go to Step 10

System OK

Important: It is VERY unlikely that the water plump 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?

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Go to Step 1

System OK