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1F-1 Engine Cooling System:
Engine Cooling System
Cooling System Description and Operation
Cooling Fan Control
The engine cooling fan system consists of 2 cooling fans
and 3 relays. The relays are powered by the battery
positive voltage circuit and controlled by a switched
ground from the powertrain control module (PCM).
During low speed operation, the PCM supplies the
ground path for the low speed cooling fan relay through
the low speed cooling fan relay control circuit. This
energizes the cooling fan low relay coil, closes the relay
contacts, and supplies battery positive voltage from the
COOL FAN LO fuse through the cooling fan motor
supply voltage circuit to the cooling fan. During high
speed operation the PCM supplies the ground path for
the cooling fan low relay through the low speed cooling
fan relay control circuit. After a 3-second delay, the PCM
supplies a ground path for the cooling fan high relay and
the s/p cooling fan relay through the high speed fan relay
control circuit.
The PCM commands the fan on under the following
conditions:
• Engine coolant temperature exceeds approximately
98°C (208°F) Low Fan Speed
• Engine coolant temperature exceeds approximately
102°C (216°F) High Fan Speed
• A/C refrigerant pressure exceeds 361 kPa (52 psi)
Low Fan Speed
• A/C refrigerant pressure exceeds 2100 kPa (300 psi)
High Fan Speed
• When the engine coolant temperature exceeds 112°C
(234°F) at key off, the fan high speed will run for up to
300 seconds. If within that time frame 102°C (216°F)
is reached then fan speed will change from high to low
speed. If within that time frame 99°C (210°F) is
reached then fan speed will change from low to off.
The PCM commands the fan off under the following
conditions:
• A/C is requested and engine speed exceeds 6,240
RPM
• Engine coolant temperature exceeds approximately
99°C (210°F) turns the cooling fans from low to off.
Engine Coolant Indicator(s)
LOW COOLANT LEVEL
The IPC illuminates the low coolant warning indicator
when any of the following occur:
• The BCM detects a low coolant level condition for at
least 30 seconds. The IPC receives a class 2
message from the BCM requesting illumination.
• The IPC performs the displays test at the start of each
ignition cycle. The indicator illuminates for
approximately 3 seconds.
General Description
Coolant Heater
The optional engine coolant heater (RPO K05) operates
using 110-volt AC external power and is designed to
warm the coolant in the engine block area for improved
starting in very cold weather −29°C (−20°F). The coolant
heater helps reduce fuel consumption when a cold
engine is warming up. The unit is equipped with a
detachable AC power cord. A weather shield on the cord
is provided to protect the plug when not in use. The
power cord has a thermal element in the cord end that
does not allow current to the heater until the ambient
temperature reaches 0°F or −18°C.
Cooling System
The cooling system's function is to maintain an efficient
engine operating temperature during all engine speeds
and operating conditions. The cooling system is
designed to remove approximately one-third of the heat
produced by the burning of the air-fuel mixture. When
the engine is cold, the coolant does not flow to the
radiator until the thermostat opens. This allows the
engine to warm quickly.
Charge Air Cooling System (LSJ Only)
The charge air cooling systems function is to reduce the
temperature of the air charge that is heated during the
supercharging process which improves the efficiency of
the supercharging system. The charge air cooling
system is a water-to-air system that uses a dedicated
electric coolant pump, a modified intake manifold, and a
separate charge air cooling radiator located between the
condenser and the radiator to cool the air charge.
Cooling Cycle
Coolant flows from the radiator outlet and into the water
pump inlet. Some coolant flows from the water pump, to
the heater core, then back to the water pump. This
provides the passenger compartment with heat and
defrost capability as the coolant warms up.
Coolant also flows from the water pump outlet and into
the engine block. In the engine block, the coolant
circulates through the water jackets surrounding the
cylinders where it absorbs heat.
The coolant then flows through the cylinder head gasket
openings and into the cylinder heads. In the cylinder
heads, the coolant flows through the water jackets
surrounding the combustion chambers and valve seats,
where it absorbs additional heat.
From the cylinder heads, the coolant flows to the
thermostat. The flow of coolant will either be stopped at
the thermostat until the engine reaches normal operating
temperature, or it will flow through the thermostat and
into the radiator where it is cooled. At this point, the
coolant flow cycle is completed.
Efficient operation of the cooling system requires proper
functioning of all cooling system components. The
cooling system consists of the following components:
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Troubleshooting
