SECTION 05B: X3 SERIES COOLING SYSTEM
PA1621 Maintenance Manual All Series | January 2017 7
2. DESCRIPTION
A radiator and variable speed electric cooling
fans are used to effectively dissipate the heat
generated by the engine. A charge air cooler
(CAC) mounted next to the radiator is also used
to cool the compressed air flow coming from the
turbocharger before it reaches the engine
intake. All components, along with the fans
circuit breaker box, are grouped together and
mounted on the L.H. side of the engine
compartment to form an easy to access and
service “cooling assembly”.
WARNING
WHEN THE ENGINE IS RUNNING
Cooling fans may activate at any moment.
Keep hands away from cooling fans or keep
the radiator door closed.
WARNING
Cooling fans may be running when the
engine is shut down in the following
conditions:
- If a High Exhaust Temperature condition
exists (e.g. following regeneration).
- During "Motor Test" sequence.
An engine mounted centrifugal water pump is
used to circulate the engine coolant in the
cooling circuit. The pump works in conjunction
with a full blocking-type thermostat positioned in
the water outlet passage, controlling the coolant
flow and providing fast engine warm-up and
regulated 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 fans 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 with a funnel through
a pressure & filler cap on the surge tank (Figure
2), the cap is also used to maintain pressure
within the system. When system exceeds
normal pressure rating (14 psi - 96.53 kPa), the
cap releases air and if necessary, coolant
through the overflow tube (Figure 2). The
thermostat is located in the housing bolted to the
engine on the L.H. side.
The engine cooling system also provides hot
coolant for the vehicle heating system. Refer to
section 22, "”HEATING AND AIR
CONDITIONING" in this manual for information
relating to heating system water circulation.
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