MBE 900 – Section 4.6 Thermostat

Section 4.6
Thermostat

The vehicle is cooled by a closed system using recirculated coolant; temperature is regulated automatically by a thermostat.‪

Section 4.6.1
Thermostat Removal

Remove the thermostat as follows:‪

PERSONAL INJURY ‪
To avoid injury from scalding, drain the radiator when the engine and coolant are cool.‪

Check the thermostat as follows:‪

Note: On 6-cylinder engines, there are two thermostats. On 4-cylinder engines, there is only one thermostat.

1. Drain the coolant from the engine.
2. For non-EGR engines remove the fuel filter housing. Refer to "2.14.1 Fuel Filter Housing Removal" .
3. Remove the upper coolant hose inlet (thermostat housing). See Figure "Thermostat Removal (6-cylinder) Non-EGR Engine" for the 6-cylinder non-EGR engine and Figure "Thermostat Removal (4-cylinder) Non-EGR Engine" for the 4-cylinder non-EGR engine, and see Figure "Thermostat Removal for EGR Engines" for EGR engines.
   

   1. Coolant Pump‪	4. Coolant Hose Inlet‪
   2. Thermostat‪	5. Mounting Bolt (3 qty.)‪
   3. O-ring‪

   Figure 1. Thermostat Removal (6-cylinder) Non-EGR Engine

   

   1. Coolant Pump‪	4. Coolant Hose Inlet‪
   2. Thermostat‪	5. Mounting Bolts (2 qty.)‪
   3. O-ring‪

   Figure 2. Thermostat Removal (4-cylinder) Non-EGR Engine

   

   1. Oil Filter and Water Pump Housing‪	6. Connector Tube‪
   2. Thermostats‪	7. Water Pump‪
   3. Bolt‪	8. Pulley‪
   4. Upper Thermostat Housing‪	9. Cab Heater Tube‪
   5. Lower Thermostat Housing‪

   Figure 3. Thermostat Removal for EGR Engines

   1. Remove the hose clamp attaching the upper coolant hose to the inlet.
   2. For non-EGR engines remove the mounting bolts attaching the inlet to the coolant pump.
   3. For EGR engines, remove three bolts securing the upper thermostat housing to lower thermostat housing.

      Note: Collect any coolant that runs out of the inlet or coolant pump.

4. Remove the thermostat(s) and O-ring(s) from the coolant pump. Discard the O-ring(s).
5. Check the thermostat(s) for proper operation. Refer to "4.6.1.1 Thermostat Checking" . Replace any thermostat that fails one or more tests.

Section 4.6.1.1
Thermostat Checking

Check the thermostat as follows:‪

Note: On 6-cylinder engines, there are two thermostats. On 4-cylinder engines, there is only one thermostat.

1. Hang the thermostat by a wire inside a container filled with water. See Figure "Heat the Thermostat" .
   

   1. Thermostat‪

   2. Container‪

   Figure 4. Heat the Thermostat

   Note: To allow the thermostat to heat evenly, make sure it is not touching the sides of the container.

   NOTICE:
   To prevent damage to the thermostat or heating container, do not ever use a welding torch or soldering gun as a source of heat.‪

2. Heat the water with a suitable heating element. Stir the water occasionally to help equalize the temperature.

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

   1. Measure the water temperature. As the temperature climbs to around 75°C (165°F), slow the rate of heating down to about 1 to 2°C (2 to 3°F) per minute.
   2. In about five minutes, the main valve should begin to open.
3. Continue to heat the water at this rate for about six to eight minutes until it reaches the opening temperature of the main valve. If the main valve is not completely open, replace the thermostat. See Figure "Thermostat Valves" .
   

   1. Thermostat‪	3. Short Circuit Valve‪
   2. Main Valve‪

   Figure 5. Thermostat Valves

4. Check all the test values listed in Table "Thermostat Test Values" . If any of the values are not met, replace the thermostat.

   Description‪	Temperature‪	Distance‪
   Main Valve Starts To Open‪	81 to 85°C (178 to 185°F)‪	—‪
   Short Circuit Valve Fully Closed‪	92°C (198°F)‪	—‪
   Main Valve Fully Open‪	95°C (203°F)‪	—‪
   Main Valve Minimum Lift (A)‪	—‪	8 mm (0.3 in.)‪

   Table 9. Thermostat Test Values
   1. At the temperature of 85°C (185°F), check that the main valve has started to open.
   2. At the temperature of 92°C (198°F), check that the short circuit valve is fully closed.
   3. At the opening temperature of 95°C (203°F), check that the main valve is fully open.
   4. Check the minimum lift of the main valve at the opening temperature.
5. Install the original or replacement thermostat(s), as necessary.
6. Install the upper coolant hose inlet and new O-ring(s) on the coolant pump.
7. Fill the engine with the removed coolant, and check for leaks and proper operation.

Section 4.6.2
Thermostat Installation

Install the thermostat as follows:‪

1. Install a new O-ring on each thermostat.
2. Install the original or replacement thermostat(s). See Figure "Breather Orifice" .

   Note: Mount each thermostat with the breather orifice pointing upward for non-EGR engines and pointing forward for EGR engines.

   

   Figure 6. Breather Orifice

3. Install the upper coolant hose inlet. See Figure "Thermostat Installation (6-cylinder)" for the 6-cylinder non-EGR engines and see Figure "Thermostat Installation (4-cylinder)" for the 4-cylinder non-EGR engines.
   

   1. Coolant Pump‪	4. Coolant Hose Inlet‪
   2. Thermostat‪	5. Mounting Bolts (3 qty.)‪
   3. O-ring‪

   Figure 7. Thermostat Installation (6-cylinder)

   

   1. Coolant Pump‪	4. Coolant Hose Inlet‪
   2. Thermostat‪	5. Mounting Bolts (2 qty.)‪
   3. O-ring‪

   Figure 8. Thermostat Installation (4-cylinder)

   1. For non-EGR engines install the mounting bolts attaching the coolant hose inlet to the coolant pump. Tighten each mounting bolts 25 N·m (18 lb·ft).
   2. For EGR engines install the mounting bolts attaching the upper thermostat housing to lower thermostat housing. Tighten bolts to 31-35 N·m (23-26 lb·ft).
   3. Install the hose clamp attaching the upper coolant hose to the inlet.
4. For non-EGR engines only, install the fuel filter housing. Refer to "2.14.2 Fuel Filter Housing Installation" .
5. Fill the engine with the removed coolant, and check for leaks and proper operation.