To determine if faulty thermostats are causing low engine coolant temperature, perform the following:
- Inspect thermostat for correct operation. Three different operating conditions occur due to the coolant inlet temperature:
- Bypass mode: When the coolant inlet temperature is <85°C (185°F) the circulating thermostat (3) is closed. The coolant circulates in the engine and coolant can flow through the vehicle heating heat exchange.
- Mixed mode: For a coolant inlet temperature of >85°C (185°F) to <95°C (203°F) the circulating thermostat opens partially and the coolant flows at the same time through the engine radiator and the short circuit line to the coolant thermostat.
- Radiator operation: When the coolant inlet temperature >95°C (203°F) the circulating thermostat is completely open. The coolant is freely flowing to the engine radiator.
- Compare the oil and coolant temperatures using DDDL 7.0. If the temperatures relate go to the next step. If not check the sensors.
- If the thermostat is not opening correctly, remove the thermostat housing from the oil cooler and replace the thermostat; refer to the EPA07 DD15 Workshop Manual (DDC-SVC-MAN-0002), “Cooling System” chapter.
ENGINE EXHAUST To avoid injury from inhaling engine exhaust, always operate the engine in a well-ventilated area. Engine exhaust is toxic. - Start and run the engine.
- Run the engine through its operating range with no-load for approximately 5 minutes, allowing the engine coolant to reach normal operating range.
- If the engine coolant temperature is 85-95°C (185-203°F), no further troubleshooting is required. Shut down the engine.
- If the engine coolant temperature is below 85-95°C (185-203°F), shut down the engine. Contact DDC Customer Support Center (313-592-5800).
