MBE 4000 DDEC VI Troubleshooting – Section 14.7 Faulty Thermostats

Section 14.7
Faulty Thermostats

To determine if faulty thermostats are causing high engine coolant temperature, perform the following:‪

1. Remove thermostat from the thermostat housing, refer to MBE 4000 Service Manual (6SE420), Chapter 4”Cooling System — Thermostat”.
2. Inspect thermostat for correct operation, refer to MBE 4000 Service Manual (6SE420), Chapter 4, “Cooling System — Thermostat”.
   1. If thermostat is fully open at 95°C (203°F), check coolant pump; refer to "14.8 Faulty Coolant Pump" .
   2. If thermostat is not fully open at 95°C (203°F), refer to "14.7.1 Thermostat Replacement" .

Section 14.7.1
Thermostat Replacement

Perform the following steps to replace thermostats:‪

1. Install new thermostat, refer to MBE 4000 Service Manual (6SE420), Chapter 4, “Cooling System — Thermostat”.
2. Verify replaced thermostat; refer to "14.7.1.1 Test Engine with New Thermostat" .

Section 14.7.1.1
Test Engine with New Thermostat

Perform the following steps to determine if thermostat replacement resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked.‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check coolant pump; refer to "14.8 Faulty Coolant Pump" .