SECTION 05: COOLING SYSTEM
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
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1. DESCRIPTION
A radiator and thermo-modulated fan are used
to effectively dissipate the heat generated by the
engine. A centrifugal-type water pump is used to
circulate the engine coolant.
One full blocking-type thermostat is used in the
water outlet passage to control the flow of
coolant, providing fast engine warm-up and
regulating coolant temperature.
The engine coolant is drawn from the lower
portion of the radiator by the water pump and is
forced through the transmission cooler before
going through the oil cooler and into the cylinder
block.
From the cylinder block, the coolant passes up
through the cylinder head and, when the engine
is at normal operating temperature, it goes
through the thermostat housing and into the
upper portion of the radiator. The coolant then
passes through a series of tubes where its heat
is dissipated by air streams created by the
revolving fan and the motion of the vehicle.
Upon starting a cold engine or when the coolant
is below normal operating temperature, the
closed thermostat directs coolant flow from the
thermostat housing through the by-pass tube to
the water pump. Coolant is recirculated through
the engine to aid engine warm up.
When the thermostat opening temperature is
reached, coolant flow is divided between the
radiator inlet and the by-pass tube. When the
thermostat is completely open, all of the coolant
flow is to the radiator inlet.
The cooling system is filled through a filler cap
on the surge tank (Figure 1), A Pressure cap is
also used to maintain pressure within the
system. When system exceeds normal pressure
rating (13 psi – 89.63 kPa), the cap releases air
and if necessary, coolant through the overflow
tube (Figure 1). A pressure relief valve is also
provided to depressurize the system before
servicing. The thermostat is located in the
housing bolted to the engine on the L.H. side.
The engine cooling system also provides hot
coolant fluid for the vehicle heating system. Refer
to section 22,
"”HEATING AND AIR
CONDITIONING"
in this manual for information
relating to heating system water circulation.
FIGURE 1: COOLANT SURGE TANK
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