Section 4.4
Thermostat

The temperature of the engine coolant is controlled by two blocking-type thermostats located in a housing attached to the right side of the cylinder head. See Figure "Thermostat and Related Parts" .‪

Figure 1. Thermostat and Related Parts

In addition to a rubber seal that is part of the thermostat, there is a lip-type seal for each thermostat that is installed in a bore in the thermostat housing. See Figure "Thermostat Seals" .‪

Figure 2. Thermostat Seals

At coolant temperatures below approximately 86 - 89°C (187 - 192°F) for vehicle the thermostat valves remain closed and block the flow of coolant from the engine to the radiator or heat exchanger. During this period, all of the coolant in the system is recirculated through the engine and is directed back to the suction side of the water pump via a bypass tube. As the coolant temperature rises above 86 - 89°C (187 - 192°F) for vehicle engines, the thermostat valves start to open, restricting the bypass system, and allowing a portion of the coolant to circulate through the radiator or heat exchanger. When the coolant temperature reaches approximately 97°C (207°F) the thermostat valves are fully open; the bypass system is blocked off, and the coolant is directed through the radiator or heat exchanger. See Figure "Cooling System Operation" .‪

Figure 3. Cooling System Operation

Properly operating thermostats are essential for efficient operation of the engine. If the engine operating temperature deviates from the normal range of 86 - 99°C (187-210°F), inspect and replace the thermostats, if necessary.‪

Section 4.4.1
Repair or Replacement of Thermostats

To determine if repair or replacement of the thermostat is necessary, perform the following procedure. See Figure "Flowchart for Repair or Replacement of Thermostats" .‪

Figure 4. Flowchart for Repair or Replacement of Thermostats

Section 4.4.2
Draining and Removal of Thermostats

Drain the thermostats as follows:‪

HOT COOLANT ‪
To avoid scalding from the expulsion of hot coolant, never remove the cooling system pressure cap while the engine is at operating temperature. Wear adequate protective clothing (face shield, rubber gloves, apron, and boots). Remove the cap slowly to relieve pressure.‪

1. Slowly open the coolant pressure control (radiator) cap.
2. Open the drain cock located on the bottom of the thermostat housing.
3. Drain the cooling system so that the coolant is below the thermostat level.

Remove the thermostats as follows:‪

1. Loosen the hose clamps on the coolant hoses connected to the thermostat housing.
2. Slide the hoses off the housing.
3. Disconnect the vent line and any other lines which are connected to the thermostat housing.
4. Remove the four thermostat housing-to-cylinder head attaching bolts.
5. Remove the thermostat housing assembly from the engine.
6. Remove the thermostats from the thermostat housing.
7. Remove and discard the thermostat housing seals.

Section 4.4.2.1
Inspection of Thermostats

Inspect thermostats as follows: ‪

1. Visually inspect all parts for wear or damage.
   1. If wear or damage is found, replace parts.
   2. If wear or damage is not found, reuse parts.
2. Visually inspect thermostat body seal for damage, cracks or nicks.
   1. If any damage is noted, replace seal.
   2. If no damage is found, reuse parts.

Section 4.4.3
Cleaning of Thermostats

Clean the thermostats as follows:‪

1. Clean all of the parts in clean fuel oil.

   EYE INJURY ‪
   To avoid injury from flying debris when using compressed air, wear adequate eye protection (face shield or safety goggles) and do not exceed 276 kPa (40 psi) air pressure.‪

2. Dry all parts with compressed air.

Section 4.4.4
Testing Thermostat

Check the operation of a thermostat as follows:‪

1. Immerse the thermostat in a metal container of water. See Figure "Checking Thermostat Operation" .
   

   Figure 5. Checking Thermostat Operation

2. Place a thermometer in the container using care not to allow the thermometer to touch the bottom or sides of the container.
3. While slowly agitating the water to maintain an even temperature, apply heat to the container. Allow at least 10 minutes for the thermostats to react before determining if the thermostats are opening in the correct temperature range.

   HOT COOLANT ‪
   To avoid scalding from the expulsion of hot coolant, never remove the cooling system pressure cap while the engine is at operating temperature. Wear adequate protective clothing (face shield, rubber gloves, apron, and boots). Remove the cap slowly to relieve pressure.‪

4. As the water is heated, the thermostat should begin to open. The nominal opening temperature (stamped on the thermostat), the start-to-open temperature range, and the full open temperature are listed in Table "Thermostat Nominal, Start-to-Open, and Fully Open Temperatures" .

   Nominal Opening Temperature (Stamped on the Thermostat) ‪	Thermostat Start-to-Open Temperature Range ‪	Fully Open Temperature ‪
   71°C (160°F)‪	69-73°C (156-163°F)‪	82°C (179°F)‪
   82°C (180°F)‪	80-84°C (176-183°F)‪	92°C (197°F)‪
   88°C (190°F)‪	86-89°C (186-193°F)‪	97°C (207°F)‪

   Table 8. Thermostat Nominal, Start-to-Open, and Fully Open Temperatures
5. Replace thermostat if it does not operate properly .

Section 4.4.5
Installation of Thermostat and Seal

Install new thermostats as follows:‪

1. Position a new seal onto seal installer (J–8550) and handle (J–7079–2) . See Figure "Positioning the Seal onto Seal Installer" .
   

   Figure 6. Positioning the Seal onto Seal Installer

2. Support the thermostat housing on a work bench so that it is level. See Figure "Thermostat Housing Seal Insertion" .
   

   Figure 7. Thermostat Housing Seal Insertion

3. Insert the seal driver with seal installed into the thermostat housing.
4. Drive the seal into the bore with a hammer until the installation tool bottoms on the housing. Rotate the tool during installation to ensure the seal is installed straight. Remove handle (J–7079–2) and installer (J–8550) . See Figure "Thermostat Housing Seal Installation" .
   

   Figure 8. Thermostat Housing Seal Installation

5. Repeat step 1 through step 4 for the other seal.
6. Coat the lip of the seals with clean engine oil.
7. Place the thermostats, spring up, into the thermostat housing.
8. Press down on the thermostats to seat them. See Figure "Seating Thermostats" .
   

   Figure 9. Seating Thermostats

9. Ensure the machined surface of the thermostat housing, where it contacts the cylinder head, is clean and dry.
10. Install the thermostat housing to the cylinder head with the four attaching bolts. Torque the bolts to 58-73 N·m (43-54 lb·ft).
11. Install the coolant hoses to the thermostat housing. Tighten the hose clamps.
12. Apply a coating of Loctite® Pipe Sealer with Teflon PT-7260 or equivalent to the threads of the drain cock if it was removed from the bottom of the thermostat housing.
13. Install and tighten the drain cock.
14. Install any other components removed for this operation.
15. Close the drain cocks in the water pump housing and at the right rear of the cylinder block.
16. Install the thermostat housing vent line and any other lines that were removed from the housing.
17. Fill the cooling system. Refer to "14.6.4 Cooling System" .
18. Refer to "12.3.5 Cooling System" for verification of thermostat installation. Listed in Table "Series 60 Engine Air System, Fuel System, and Cooling System Parameters" are the normal cooling system operational parameters.