Testing Thermostats

Removing Thermostats

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.

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   Remove Thermostat Cover

   
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   Remove Thermostat Gasket and Thermostats

   Visually inspect area around thermostat cover for leaks.

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

3. Remove bypass tube from coolant pump and thermostat cover.

4. Remove coolant return line from thermostat cover.

5. Remove seven cap screws from thermostat cover and remove cover (if not previously done).

6. Remove gasket and remove thermostats.

7. Test each thermostat for proper opening temperature.

Testing Thermostats Opening Temperature

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   Thermostat and Thermometer in Water

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

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2. Inspect thermostat ball valve in vent notch. If ball valve movement is restricted, and cleaning does not free ball valve, replace thermostat.

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 specifications.

   Item	Measurement	Specification
   Thermostat	Start to Open	85 °C (185 °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 all thermostats.

Installing Thermostats

IMPORTANT: Top thermostat has a vent notch with ball valve for air bleeding. Ball valve MUST BE installed at 12 o’clock position.

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   Install Thermostats

   
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   Install Thermostat Cover

   Clean all gasket material from thermostat cover and mounting surfaces.

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2. Install thermostats in cover.

   NOTE: Thermostats are identical and can be placed in any arrangement.

3. Install a new gasket on thermostat cover.

4. Install thermostat cover using seven cap screws and tighten to specifications.

   Item	Measurement	Specification
   Thermostat Cover Cap Screws	Torque	50 N·m (37 lb.-ft.)

   Item	Measurement	Specification
   Coolant Bypass Tube Cap Screws	Torque	37 N·m (27 lb.-ft.)

5. Install coolant return line from rear of cylinder head. Tighten fitting to specifications.

   Item	Measurement	Specification
   Coolant Return Line Fitting	Torque	14 N·m (124 lb.-in.)

6. Pressure test the cooling system a second time to be sure that thermostat cover gasket is sealing properly. (See Pressure Testing Cooling System in the Lubrication & Maintenance — 500 Hours/12 Months Section).