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SERIES 40E THERMOSTAT OPERATION

When the engine coolant temperature is below the specified thermostat opening temperature, the coolant flows through the bypass passage to the water pump because the radiator outlet port is blocked. As the engine reaches operating temperature, the thermostat opens, directing coolant towards the radiator. This also restricts the bypass opening. See Figure 31554 . ‪

1. Thermostat ‪

Thermostat Operation

Removal of Thermostat

Follow these steps to remove the thermostat. ‪

  1. Loosen the worm clamp at the water outlet hose and remove it from the thermostat.
  2. Remove the two flanged head bolts that secure the thermostat to the cylinder head. See Figure 31977 .

    1. Thermostat ‪

    2. Cylinder Head ‪

    Thermostat Removal

  3. Remove the thermostat from the cylinder head. Remove and discard the O-ring. See Figure 31978 .

    1. Thermostat ‪

    3. Cylinder Head ‪

    2. O-ring ‪

    Thermostat Removal

Inspection of Thermostat

Follow these steps to inspect the thermostat and the operation. ‪

  1. Inspect thermostat for cracks and pitting.

    NOTICE:

    When servicing thermostats, it is essential that the thermostat opens fully at the specified temperature to avoid an overheating condition that may cause engine damage. ‪

  2. Check the thermostat operation as follows. See Figure 31979 .

    1. Thermostat ‪

    4. Thermometer ‪

    2. Suspension Line ‪

    5. Heat Source ‪

    3. Ribbon ‪

    Thermostat Operation Check

    Note: Only genuine Detroit Diesel thermostats ensure proper coolant flow and positive sealing characteristics required to provide proper engine cooling. Effective with January 1998 production, 88 - 100C (190 - 212F) thermostats are used in Series 40E engines to reduce exhaust emissions. The former 82 - 94C (180 - 202F) thermostat will no longer be serviced.

    To avoid injury from scalding, use lifting tools and wear heat-resistant gloves when retrieving the thermostat from boiling water.

    1. Manually open the thermostat enough to insert a nylon ribbon under the valve seat. Suspend the thermostat in the container so the thermostat does not touch the bottom of the container.
    2. Heat the container filled with water to "START-TO-OPEN " temperature of 187F- 192F (86 - 89C). Observe thermometer and record temperature as soon as thermostat drops from nylon ribbon. This is the "start-to-open" temperature.
    3. Continue to heat water to "FULL-OPEN " temperature of 205F (96C). Observe the thermometer and movement of the thermostat. Observe the thermostat movement when FULL-OPEN temperature is achieved. Minimum travel at FULL- OPEN temperature is 9.0 mm (.410 in.). See Figure 31980 .
    4. 1. Thermostat ‪

      Thermostat

      To avoid injury from scalding, use lifting tools and wear heat-resistant gloves when retrieving the thermostat from boiling water.

    5. Remove the thermostat from water. Inspect the seat area for pitting and foreign deposits.
    6. Replace the thermostat if it does not operate as described or meet visual inspection criteria.
  3. Visually inspect thermostat for the following conditions that may cause improper closure. Replace as required.
    1. Debris or loose fit at seat.
    2. Rough or uneven wear at seal seat location.
    3. Uneven seat.

Installation of Thermostat Assembly

Follow these steps to install the thermostat assembly to the cylinder head. ‪

  1. Install a new O-ring onto the thermostat assembly See Figure 31978 .

    1. Thermostat ‪

    3. Cylinder Head ‪

    2. O-ring ‪

    Thermostat Installation

  2. Install the thermostat assembly into the opening on top of the cylinder head and secure with flanged head bolts. Torque bolts to specifications. Refer to Specifications in Section .