DETROIT DIESEL 53
The temperature of the In-line engine coolant is controlled by a single choke type thermostat located in a housing
attached to the water outlet end of the cylinder head.
On the In-line engines, a by-pass tube is attached between the thermostat housing and the water pump.
At coolant temperatures below approximately 170°F., the thermostat valve remains closed and blocks the flow of coolant
through the radiator or heat exchanger. During this period, the coolant circulates through the cylinder block and head and
then back to the suction side of the pump via the by-pass tube. As the coolant temperature rises, the thermostat valve
begins to open, restricting the by-pass system and permits the coolant to circulate through the radiator or heat
With the valve fully opened in the in-line engine, a very small portion of the coolant will continue to circulate through the
by-pass tube, while the major portion will pass through the radiator.
A properly operating thermostat is essential for efficient operation of the engine. If the engine operating temperature
deviates from the normal range of 160°F - 185°F., remove and check the thermostat(s).
Drain the cooling system to the necessary level by opening the drain valves.
Fig. 2. Thermostat Housing Details and Relative Location of Parts (In-Line Engine)