Testing Thermostats

CAUTION:

RG13860
RG13860-UN-17JAN05

Remove Thermostat Cover

A - Thermostat Cover

Explosive release of fluids from pressurized cooling system can cause serious burns. Do not drain coolant until coolant temperature is below operating temperature. Always loosen cooling system filler cap, radiator cap or drain valve slowly to relieve pressure.

  1. Visually inspect the area around the coolant manifold for leaks. Partially drain coolant from the cooling system.

  2. Remove thermostat cover (A).

  3. RG13861
    RG13861-UN-12APR05

    Removing Thermostats

    Inspect thermostats.


  4. Test each thermostat for proper opening temperature.


Testing Thermostats Opening Temperature

RG5971
RG5971-UN-23NOV97

Thermostats and Thermometer in Water

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

  2. Inspect thermostat with wiggle wire in vent notch. If wire movement is restricted, replace thermostat if cleaning does not free movement.

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

    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 specification given in chart below.

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

    THERMOSTAT TEST SPECIFICATIONS
     

    Rating

    Initial Opening

    (Range)

    Full Open

    (Nominal)
     

    82°C (180°F)

    80—84°C (175—182°F)

    94°C (202°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 one thermostat is defective, replace both thermostats.


Installing Thermostats

  1. RG13861
    RG13861-UN-12APR05

    Installing Thermostats

    Install new rubber seal on each thermostat and install thermostats.


  2. Install cover and tighten cap screws to specifications.

    ItemMeasurementSpecification
    Cast Iron Thermostat Cover Cap ScrewsTorque45 N˙m (33 lb-ft)

    IMPORTANT: Air must be expelled from cooling system when system is refilled. Loosen temperature sending unit fitting at rear of cylinder head or plug in thermostat housing to allow air to escape when filling system. Retighten fitting when all air has been expelled. Damage to EGR cooler (if equipped) could result if cooling system is not bled properly.

  3. Pressure test the cooling system a second time to be sure the thermostat cover is sealed (See Pressure Testing Cooling System , in Lubrication And Maintenance 500 Hour/12 Months).

JG50163,000028E-19-20120413