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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 232 (Engine Cooling System) >> Diagnostic Information and Procedures >> Fan Clutch Diagnosis >> Engine Overheating

Engine Overheating

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CAUTION: Check for adequate clearance between the fan blades and the thermometer sensor before starting the engine, as damage could occur.

Use the following procedure in order to diagnose the causes of engine overheating:

  1. Ensure that the engine is cool. This will allow complete disengagement of the fan clutch.

    Important:  Testing the fan clutch by rotating the fan in a repeated clockwise/counterclockwise motion causes the clutch to free-wheel. Free-wheeling is a normal result of rotating the fan in this manner. Conduct further tests in order to determine if it is necessary to replace the fan clutch.

  2. Spin the fan and clutch assembly by hand.

    If the fan and clutch assembly easily revolves more than 5 times with no drag, replace the fan clutch.

  3. If the fan clutch performs correctly but exhibits drag, position a thermometer between the fan blades and the radiator.

    Use any of the following methods in order to position the thermometer:

    • Insert the thermometer sensor through one of the existing holes in the fan shroud.
    • Place the thermometer between the radiator and the shroud.
    • On models that do not have holes in the fan shroud, drill a 5 mm (3/16 in) hole in the fan shroud. Insert the thermometer in the hole.
  4. Cover the radiator in order to induce a high engine temperature.
  5. Start the engine.
  6. Turn on the air conditioning.
  7. Operate the engine at 2,000 RPM.
  8. Wait for 5 to 10 minutes while the temperature increases sufficiently to allow the fan clutch to engage. The following conditions indicate that the fan clutch has engaged:
    • A roaring noise or an increase in fan noise occurs.
    • The thermometer reading drops approximately 3-10°C (5-15°F).

      Important:  Do not continue the test past a thermometer reading of 88°C (190°F). Continuing the test past a thermometer reading of 88°C (190°F) may cause engine overheating.

  9. Observe the thermometer reading when the fan clutch engages.

    The following conditions are cause for replacement of the fan clutch:

    1. The fan clutch does not engage while the temperature measures 65-90°C (150-195°F).

      If the fan clutch does not engage while the temperature is within this range, verify that the fan clutch was disengaged at the beginning of the test.

    2. Both of the following conditions exist:
      • No temperature drop occurs
      • The fan noise level is constant from the beginning of the test until the time when the engine temperature reaches 88°C (190°F).

        Do not continue the test past a thermometer reading of 88°C (190°F) in order to prevent overheating.

  10. Perform the following steps as soon as the fan clutch engages:
    1. Remove the radiator cover.
    2. Turn OFF the air conditioning.
    3. Operate the engine at approximately 1,500 RPM until the coolant returns to the normal operating temperature.
  11. Observe the operation of the fan clutch.

    The fan clutch should disengage after several minutes. Disengagement of the fan clutch is indicated by a decrease in fan noise or roar.

    If the fan clutch does not disengage after several minutes, the fan clutch should be replaced.

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