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4LHD/4LHDX Application Manual
Powertrain Control Solutions
REV 1.1
2.3.2 Cooler Requirements
To provide proper operation and longevity, the cooling system must maintain the transmission sump temperature below
132°C (270°F) and stator temperature below 177°C (350°F) at all times. This is defined as a “never exceed” limit under
all operating conditions. Average sump temperature must not exceed 110°C (230°F). The cooler must be capable of 4-5
kW of heat rejection for light duty applications, and 8-10 kW for heavy use such as industrial vehicles, off road equipment,
military and ground support equipment.
2.3.3 Cooler Lines
Cooler Line Connection:
Cooler lines connect the transmission to the radiator (cooler). Cooler lines should be as short,
and with as few bends as possible. The largest feasible pipe bore should be used. Routing should avoid external heat
sources (such as exhaust pipes, catalytic converters etc.), protect the pipe from road hazards and provide for ease of
installation and removal. The cooler lines should be adequately supported along their length to prevent vibrations from
generating noise or fatigue distress, and to prevent noise transmission into the vehicle structure.
Flow Requirements:
The transmission cooler lines and the oil cooler must flow a minimum of 6 LPM at 345 kPa (50 psi)
and 11 LPM at 690 kPa (100 psi). The flow test shall be run with 93˚C (200˚F) ATF.
Pressure Requirements
: Cooler line pressure under normal operation will be between 200 kPa (30 psi) and 1,000 kPa
(150 psi). The transmission may produce pressure of up to 2,086 kPa (300 psi) at the cooler line entrance. This pressure
may be observed on start up or if there is blockage in the transmission cooling system (cooler lines, oil cooler, return fitting
at transmission). The lines and fittings must all be rated for a minimum of 300 psi.
Temperature Requirements:
The cooler lines, cooler, and fittings shall be capable of withstanding fluid temperatures of
177˚C (350˚F).
Figure 2.3.3-1 Cooler Line Connection
Rev
Sheet 62
24214609
3.2. Thermal Requirements
3.2.1. Cooling
Transmission fluid is heated primarily by the pumping action that occurs within the torque
converter. Heat load varies, depending on speed, grade, duty cycle, ambient
temperature, etc. A method of heat dissipation must be provided in order to maintain
proper transmission temperature.
Cooling is accomplished by circulating the fluid through a cooler that is external to the
transmission. Incorporation of the cooler within the radiator is recommended since this
provides the added advantage of quick warm-up of the transmission in cold climates. If
the cooler is located in a radiator end tank, the inlet pipe should be at the lowest point of
the cooler.
If an auxiliary cooler is used, it should be located in the return line to the transmission,
and the system should incorporate a bypass to allow lubrication flow under very low
ambient temperature conditions. Adequate flow shall be verified by test.
3.2.1.1. Cooler Line Connection
Cooler lines connect the transmission to the radiator (cooler). Refer to Figure 3.2.1.1-1
for the position of the “to cooler” and “from cooler” connections.
Cooler lines should be as short, and with as few bends as possible. The largest
feasible pipe bore should be used. Routing should avoid external heat sources (such
as exhaust pipes, catalytic converters etc.), protect the pipe from road hazards and
provide for ease of installation and removal. The cooler lines should be adequately
supported along their length to prevent vibrations from generating noise or fatigue
distress, and to prevent noise transmission into the vehicle structure. The cooler
circuits should be capable of withstanding 2068 kPa (300 psi) and fluid temperatures
of 177
˚
C (350
˚
F).
FIGURE 3.2.1.1-1 Cooler Line Connection
➤
FROM COOLER
➤
TO COOLER
