MBE4000 APPLICATION AND INSTALLATION
7.3
THERMOSTAT
The temperature of the engine coolant is controlled by two blocking-type thermostats located
in a housing on the front of the cylinder head. See Figure 7-4.
1. Mounting Bolt
4. O-ring
2. Thermostat Housing
5. Thermostat
3. Upper Coolant Tube
8. Coolant Pump Housing
Figure 7-4
Thermostat and Related Parts
In addition to a rubber seal that is part of the thermostat, there is a lip-type seal for each thermostat
that is installed in a bore in the thermostat housing.
At coolant temperatures below the operating range the thermostat valves remain closed and block
the
fl
ow of coolant from the engine to the radiator.
During this period, all of the coolant in the system is recirculated through the engine and is
directed back to the suction side of the water pump via an internal bypass tube. As the coolant
temperature rises above the start–to–open temperature, the thermostat valves begin to open,
restricting the bypass system, and allowing a portion of the coolant to circulate through the
radiator. When the coolant temperature reaches an approximate fully open temperature, the
thermostat valves are fully open, the bypass system is blocked off, and the coolant is directed
through the radiator. Thermostat closing and opening temperatures are listed in the “Technical
Data” section of this manual (refer to section 14).
Properly operating thermostats are essential for ef
fi
cient operation of the engine.
All information subject to change without notice.
(Rev. 03/06)
7-7
7SA250 0603
Copyright © 2006 DETROIT DIESEL CORPORATION