Testing Thermostats Opening Temperature


To Remove Thermostats

  1. CAUTION: Explosive release of fluids from pressurized cooling system can cause serious burns. DO NOT drain coolant until it has cooled below operating temperature. Always loosen radiator pressure cap or drain valve slowly to relieve pressure.

    TS281
    TS281-UN-15APR13

    High Pressure Fluids

    RG13737
    RG13737-UN-11NOV04

    Thermostat Cover

    A - Thermostat Cover

    Visually inspect area around thermostat housing for leaks.


  2. Remove radiator pressure cap and partially drain cooling system.

  3. Remove thermostat cover (A). Clean and check cover for cracks or damage

  4. NOTE: Some earlier 6.8 L engines may have one non-blocking thermostat. Replace the non-blocking thermostat with a partial blocking thermostat. See your engine distributor.

    RG14362
    RG14362-UN-06JAN06

    Thermostats

    A - Thermostats

    B - Rubber Seal

    Remove all three thermostats (A) from the housing.


  5. Remove and discard rubber seal (B) from each of the three thermostats.


Testing Thermostats Opening Temperature

RG5971
RG5971-UN-23NOV97

Testing Thermostat Opening Temperature

  1. NOTE: Perform the following test for the two blocking thermostats as well as for the non-blocking thermostat.

    Remove thermostats.

  2. Visually inspect thermostats for corrosion or damage. Replace as a matched set as necessary.

    CAUTION: DO NOT allow thermostat or thermometer to rest against the side or bottom of container when heating water. Either may rupture if overheated.

  3. Suspend thermostat and a thermometer in a container of water.

  4. Stir the water as it heats. Observe opening action of thermostat and compare temperatures with the specification given in chart below.

    NOTE: Due to varying tolerances of different suppliers, initial opening and full open temperatures may vary slightly from specified temperatures.

    THERMOSTAT TEST SPECIFICATIONS

    Rating

    Initial Opening (Range)

    Full Open (Nominal)

    71°C (160°F)

    69—72°C (156—162°F)

    84°C (182°F)

    77°C (170°F)

    74—78°C (166—172°F)

    89°C (192°F)

    82°C (180°F)

    80—84°C (175—182°F)

    94°C (202°F)

    89°C (192°F)

    86—90°C (187—194°F)

    101°C (214°F)

    90°C (195°F)

    89—93°C (192—199°F)

    103°C (218°F)

    92°C (197°F)

    89—93°C (193—200°F)

    105°C (221°F)

    96°C (205°F)

    94—97°C (201—207°F)

    100°C (213°F)

    99°C (210°F)

    96—100°C (205—212°F)

    111°C (232°F)

  5. Remove thermostat and observe its closing action as it cools. In ambient air the thermostat should close completely. Closing action should be smooth and slow.

  6. If any thermostat is defective, replace all three thermostats.


To Install Thermostats

RG14362
RG14362-UN-06JAN06

Installing Thermostats

A - Thermostats

B - Rubber Seal

  1. Install new rubber seal (A) for each thermostat.

  2. IMPORTANT: Install each thermostat in the same location from which it was removed.

    Install thermostats into housing.

  3. Install thermostat cover and tighten thermostat cover cap screws to specifications.

    ItemMeasurementSpecification
    Thermostat Cover Cap ScrewTorque73 N·m (55 lb-ft)

  4. If not already done, fill cooling system and check for leaks.

    IMPORTANT: Air must be expelled from cooling system when system is refilled. Loosen plug on top of thermostat housing to allow air to escape when filling system. Retighten plug after filling cooling system.

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