COOLING SYSTEM
Thermostat
A full blocking thermostat is used to automatically regulate coolant temperature by controlling
the coolant
fl
ow to the radiator and engine bypass circuit. A full blocking thermostat design in
the full open position (8° to 9°C [15° to 17°F] above the start to open temperature) controls the
engine bypass circuit, and provides maximum coolant
fl
ow to the radiator.
The start-to-open thermostat temperature is 83°C (181°F). The full-open thermostat temperature
is 95°C (203°F). The engine coolant temperature will be controlled at the thermostat start to
open value, under normal operating conditions.
NOTICE:
Never operate the engine without thermostats.
Coolant Sensor Devices
Engine coolant temperature monitors (gauges, alarms, shutdowns, fan and shutter control
switches, etc.)
must
be durable, reliable and accurate. Submerge the probe completely in a high
fl
ow stream to sense uniform coolant temperature. Locate the probe in an area without air pockets,
or mount it in a place where it will not be affected by coolant being returned from parallel circuits
such as heater, air compressor, and aftercooler return lines.
The coolant temperature monitor may not respond fast enough to prevent engine damage if a large
quantity of coolant is suddenly lost, or if the water pump becomes air bound. Engine Coolant
Level Sensors are required with MBE4000 engines.
Temperature Gauges:
Every temperature gauge should have suf
fi
cient markings to allow an
operator to determine actual operating temperature. The temperature range should go beyond
99°C (210°F) so the operator will know if the maximum coolant temperature is being exceeded.
Maintain accuracy of 3°C (+/- 5°F) to prevent inaccurate indication of either hot or cold running
engine conditions.
Temperature Alarms:
An auxiliary warning device (audible or visible) should be included if
a digital gauge is used. Set temperature alarm units at coolant temperature level that is 3°C
(5°F) above the maximum allowable coolant temperature. Accuracy should be 3°C (+/- 5°F).
Locate each alarm sensor before the thermostat. Special considerations, including testing
must
be
done when a coolant recovery system is used.
Temperature Shutdowns:
Set temperature shutdown devices for a coolant temperature level of
105°C (223°F). Accuracy should be 1°C (+/- 2°F).
Low Coolant Level Sensor:
Locate the sensor for low engine coolant level in the top tank. See
tank design section for additional recommendations.
Shutter Control Switches:
Mount shutter switches before the engine thermostat so they can
sense engine coolant temperature. The various temperature control devices (shutters, fan drives
and thermostats)
must
operate in proper sequence to prevent coolant temperature instability or
overheat conditions.
7-44
All information subject to change without notice.
(Rev. 03/06)
7SA250 0603
Copyright © 2006 DETROIT DIESEL CORPORATION