Description - PREVOST H3-41 Maintenance Manual

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 airstreams 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 H3 Series cooling system is filled with a
funnel through a pressure & filler cap on the
surge tank, 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 3). On
the X3 Series, the cap is also present on the
surge tank to act as a pressure cap, but the fill
cap is on the top of a plastic recovery tank
located next to the surge tank (Figure 2). The
thermostat is located in the housing bolted to the
engine on the L.H. side.
On X3-Series vehicles do not open the surge
tank pressure cap unless a large amount of
liquid must be added. Always use the recovery
tank fill cap to add coolant to the vehicle
during normal operation (level check).
On X3 Series vehicles, the system pressure
must be relieved using the pressure relief
valve.
Never open the surge tank pressure cap
without making sure first that the system is
completely depressurized. Coolant under
pressure (hot or not) may cause serious
injuries and eyes damages.
NOTE
Close the valve after releasing the pressure.
The engine cooling system also provides hot
coolant for the vehicle heating system. Refer to
section
CONDITIONING" in this manual for information
relating to heating system water circulation.
PA1621 Maintenance Manual All Series
SECTION 05: COOLING SYSTEM
WARNING
WARNING
22,
""HEATING
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Section 05 revised Feb 2019
AND AIR
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