MBE 4000 – Section 4.5 Thermostat

Section 4.5
Thermostat

Perform the following procedures for removal and installation of the thermostat.‪

Section 4.5.1
Thermostat Removal

Remove the thermostat 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. Drain the coolant from the engine. Refer to "4.1.1 Cooling System Draining and Flushing" .
2. Remove the upper coolant tube from the thermostat housing. See Figure "Thermostat Removal or Installation" .
   

   1. Mounting Bolt‪	4. O-ring‪
   2. Thermostat Housing‪	5. Thermostat‪
   3. Upper Coolant Tube‪	6. Coolant Pump Housing‪

   Figure 1. Thermostat Removal or Installation

3. Remove the mounting screws attaching the thermostat housing to the coolant pump housing. Remove the thermostat housing.

   Note: Catch any coolant that runs out of the upper coolant tube or coolant pump housing.

4. Remove the thermostats and O-rings from the coolant pump housing. Discard the O-rings.
5. Check both thermostats for proper operation. For detailed procedures, refer to "4.5.2.1 Thermostat Checking" . Replace any thermostat that fails one or more tests.

Section 4.5.2
Thermostat Installation

Install the thermostat as follows:‪

1. Install a new O-ring on each thermostat.
2. Install the original and/or replacement thermostats.
3. Install the thermostat housing. Install the mounting bolts attaching the thermostat housing to the coolant pump housing. Tighten each mounting bolt 25 N·m (18 lb·ft). See Figure "Thermostat Removal or Installation" .
4. Install the upper coolant tube on the thermostat housing. Tighten the hose clamp until firm.
5. Fill the engine with coolant, and check for leaks and proper operation. Refer to "4.1.1 Cooling System Draining and Flushing" .

Section 4.5.2.1
Thermostat Checking

Check the thermostat as follows:‪

1. Remove the thermostat from the coolant pump. Refer to "4.5.1 Thermostat Removal" .
2. Hang the thermostat by a wire inside a container filled with water. See Figure "Heat the Thermostat" .
   

   1. Thermostat‪

   2. Container‪

   Figure 2. 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. ‪

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

   PERSONAL INJURY ‪
   To avoid injury from hot surfaces, wear protective gloves, or allow engine to cool before removing any component.‪

   1. Measure the water temperature. As the temperature climbs to around 165°F (75°C), slow the rate of heating down to about 2 – 3°F (1 – 2°C) per minute.
   2. In about five minutes, the main valve should begin to open.
4. 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 Lift" .
   

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

   Figure 3. Thermostat Lift

5. Check all the test values for the main valve listed in Table "Thermostat Test Values" . If any of the values is not met, replace the thermostat.

   Description ‪	Temperature – °C (°F) ‪	Distance mm (in.) ‪
   Main Valve Starts To Open‪	81 – 85 (177 – 185)‪	—‪
   Main Valve Fully Open‪	95 (203)‪	—‪
   Main Valve Minimum Lift‪	—‪	8 (0.3)‪
   Short Circuit Valve Fully Closed‪	92 (198)‪	—‪
   Short Circuit Valve Minimum Lift‪	—‪	6 to 7.5 (0.24 to 0.295)‪

   Table 7. Thermostat Test Values
   1. At the temperature of 85°C (185°F), check that the main valve has started to open.
   2. At the opening temperature of 95°C 203°F), check that the main valve is fully open.
   3. Check the minimum lift of the main valve at the opening temperature.
6. Check all the test values for the short circuit valve listed in Table "Thermostat Test Values" . If any of the values is not met, replace the thermostat.
   1. At the temperature of 92°C (198°F), check that the short circuit valve is fully closed.
   2. Check the minimum lift of the short circuit valve at the closing temperature.
7. Install the original or replacement thermostat(s), as necessary, the upper coolant hose inlet, and O-ring(s) on the coolant pump, as removed.
8. Fill the engine with coolant, as removed, and check for leaks and proper operation.