Workshop Manual

30.1 DESCRIPTION AND OPERATION OF COOLANT THERMOSTAT

Thermostat Operating Modes

The coolant from the radiator and the radiator bypass mix i n the thermostat housing. The

thermostat regulates the temperature of this mixed ﬂow circuit.

Three different operating conditions occur due to the coolant mixed ﬂow temperature:

□ Bypass mode: When the coolant mixed ﬂow temperature is below 87°C (188°F), the

circulating thermostat is closed. The coolant circulates through the radiator bypass to the

coolant thermostat. None of the ﬂow passes through the radiator.

□ Mixed mode: For a coolant mixed ﬂow temperature above 87°C (188°F) to and less than

95°C (203°F), the circulating thermostat opens partially and the coolant ﬂows at the same

time through the engine radiator and the radiator bypass to the coolant thermostat .

□ Radiator operation: When the coolant inlet temperature is above 95°C (203°F) the

circulating thermostat is completely open. The coolant ﬂows through the radiator to the

coolant thermostat. None of the ﬂow passes through the radiator bypass.

Other minor coolant l oops exist in addition to those described above. The ﬂow through these

loops are unaffected by the position of the coolant thermostat. These loops include the ﬂow

through the vehicle cab heater, vehicle bunk heater, the EGR actuator, and the doser.

All information subject to change without notice.