exj 7a, JEEP Manuals, Electronic Service Manual (jeep cherokee xj do 2000)
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XJ
COOLING SYSTEM
7 - 1
COOLING SYSTEM
TABLE OF CONTENTS
page
page
DESCRIPTION AND OPERATION
DIAGNOSIS AND TESTING
SERVICE PROCEDURES
REMOVAL AND INSTALLATION
CLEANING AND INSPECTION
COOLING SYSTEM CLEANING/REVERSE
SPECIFICATIONS
DESCRIPTION AND OPERATION
COOLING SYSTEM COMPONENTS
The cooling system consists of:
²
COOLING SYSTEM
Charge Air Cooler
²
Electric Cooling Fan
DESCRIPTION
The cooling system regulates engine operating tem-
perature. It allows the engine to reach normal oper-
ating temperature as quickly as possible, maintains
normal
²
An aluminum radiator with plastic side tanks
²
A radiator mounted fill vent valve
²
A separate pressurized coolant tank
A threaded-on, pressure/vent cap mounted to the
coolant tank
²
²
operating
temperature
and
prevents
over-
Cooling fan (mechanical)
heating.
The cooling system also provides a means of heat-
ing the passenger compartment. The cooling system
is pressurized and uses a centrifugal water pump to
circulate coolant throughout the system. A water
manifold collects coolant from the cylinder heads. A
separate and remotely mounted, pressurized coolant
tank using a pressure/vent cap is used.
²
Thermal viscous fan drive
²
Fan shroud
²
Thermostat
²
Coolant
²
Low coolant level sensor
²
Low coolant warning lamp
²
Coolant temperature gauge
²
Water pump
²
Hoses and hose clamps
 7 - 2
COOLING SYSTEM
XJ
DESCRIPTION AND OPERATION (Continued)
COOLANT ROUTING
For cooling system flow routing, refer to (Fig. 1)
Fig. 1 Coolant Flow—2.5L Diesel Engine—Typical
1 – PRESSURIZED COOLANT TANK
2 – PRESSURE/VENT CAP
3 – HOSE
4 – HEATER HOSES
5 – HEATER CORE
6 – WATER MANIFOLD FITTING
7 – WATER MANIFOLD (TOP OF CYLINDER HEAD)
8 – ENGINE (TOP VIEW)
9 – UPPER RADIATOR HOSE
10 – RADIATOR
11 – THERMOSTAT
12 – FILL VENT CAP
13 – WATER PUMP
14 – LOWER RADIATOR HOSE
15 – VENT HOSE
16 – LARGER FITTING TO COOLANT TANK
17 – HOSES
18 – HOSE
19 – ENGINE OIL COOLER
20 – LOW COOLANT LEVEL SENSOR
XJ
COOLING SYSTEM
7 - 3
DESCRIPTION AND OPERATION (Continued)
RADIATOR
DESCRIPTION
The radiator used with the 2.5L diesel is con-
structed of a horizontal flow aluminum core with
plastic side tanks.
CAUTION: Plastic tanks, while stronger than brass,
are
subject
to
damage
by
impact,
such
as
wrenches.
ENGINE ACCESSORY DRIVE BELT
DESCRIPTION
The accessory drive components are operated by a
single, crankshaft driven, serpentine drive belt. An
automatic belt tensioner is used to maintain correct
belt tension at all times.
Fig. 2 Pressurized Coolant Tank
1 – LOW COOLANT LEVEL SWITCH
2 – COOLANT RESERVOIR
3 – LOW COOLANT LEVEL SWITCH HARNESS CONNECTOR
CAUTION: When installing a serpentine accessory
drive belt, the belt MUST be routed correctly. If not,
the engine may overheat due to water pump rotat-
ing in wrong direction.
A drain hose is attached to this tube. The water
pump seals is lubricated by the antifreeze in the cool-
ant mixture. No additional lubrication is necessary.
A rubber o-ring (instead of a gasket) is used as a
seal between the water pump and the water pump
adapter (Fig. 3).
A quick test to determine if the pump is working is
to check if the heater warms properly. A defective
water pump will not be able to circulate heated cool-
ant through the heater hoses and the heater core.
COOLANT TANK
DESCRIPTION
A pressurized, plastic coolant tank is used with
this cooling system (Fig. 2). The tank is located at
the right-rear side of the engine compartment and is
mounted as the highest point of the cooling system.
This allows any air or vapor exceeding the pressure/
vent cap rating to escape through the cap. Coolant
flows through the tank at all times during engine
operation whether the engine is cold or at normal
operating temperature. The coolant tank is equipped
with a threaded pressure/vent cap. Refer to Pressure/
Vent Cap for additional information.
The low coolant level sensor is located near the
bottom of the tank (Fig. 2).
COOLANT
DESCRIPTION
Coolant flows through the engine water jackets
and cylinder heads absorbing heat produced by the
engine during operation. The coolant carries heat to
the radiator and heater core. Here it is transferred to
the ambient air passing through the radiator and
heater core fins.
WATER PUMP
LOW COOLANT LEVEL SENSOR
DESCRIPTION
A centrifugal water pump circulates coolant
through the water jackets, passages, water manifold,
radiator core, pressurized coolant tank, cooling sys-
tem hoses and heater core. The pump is driven from
the engine crankshaft by a drive belt. The water
pump is bolted to the water pump adapter (Fig. 3).
The water pump adapter is bolted to the engine.
The water pump impeller is pressed onto the rear
of a shaft that rotates in bearings pressed into the
housing. The bottom of the housing is equipped with
a small vent tube (Fig. 3) to allow seepage to escape.
DESCRIPTION
The low coolant level sensor checks for low coolant
level in the coolant tank (Fig. 4).
OPERATION
When the coolant level gets low a signal will be
sent from this sensor to the powertrain control mod-
ule (PCM). When the PCM determines low coolant
level, the instrument panel mounted low coolant level
warning lamp is illuminated. The sensor is located
 7 - 4
COOLING SYSTEM
XJ
DESCRIPTION AND OPERATION (Continued)
Fig. 4 Low Coolant Level Sensor
1 – PRESSURE/VENT CAP
2 – PRESSURIZED COOLANT TANK
3 – LOW COOLANT LEVEL SENSOR
the radiator. This provides quicker engine warmup
and overall temperature control.
The same thermostat is used for winter and sum-
mer seasons. An engine should not be operated with-
out a thermostat, except for servicing or testing.
Operating without a thermostat causes other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance, increased exhaust
emissions and crankcase condensation. This conden-
sation can result in sludge formation.
Fig. 3 Water Pump— Typical
1 – O-RING SEAL
2 – WATER PUMP ADAPTER
3 – DRAIN HOSE
4 – WASHER
5 – PUMP MOUNTING BOLTS (4)
6 – WASHER
7 – WATER PUMP PULLEY BOLTS (3)
8 – WATER PUMP PULLEY
9 – VENT TUBE
10 – PUMP HUB
11 – WATER PUMP
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
PRESSURE/VENT CAP
DESCRIPTION
The pressure/vent cap is threaded-on to the coolant
tank. This cap releases excess pressure at some point
within a range of 90-117 kPa (13- 17 psi). The actual
pressure relief point (in pounds) is labeled on top of
the cap (Fig. 5).
on the front of the coolant tank (Fig. 4). For informa-
tion,
refer
to
Group
8E,
Instrument
Panel
and
Gauges.
If this lamp is illuminated, it indicates the need for
service.
OPERATION
The cooling system will operate at pressures up to
103 kPa (15 psi). This results in a higher coolant
boiling point allowing increased radiator cooling
capacity. The cap (Fig. 5) contains a spring-loaded
pressure relief valve. This valve opens when system
pressure reaches approximately 103 kPa (15 psi).
When the engine is cooling down, vacuum is
formed within the cooling system. To prevent collapse
of the radiator and coolant hoses from this vacuum, a
vacuum valve is used within the cap. This valve pre-
vents excessive pressure differences from occurring
THERMOSTAT
DESCRIPTION
A pellet-type thermostat controls the operating
temperature of the engine by controlling the amount
of coolant flow to the radiator.
OPERATION
The thermostat starts to open at 80°C (176°F).
Above this temperature, coolant is allowed to flow to
 XJ
COOLING SYSTEM
7 - 5
DESCRIPTION AND OPERATION (Continued)
ponents may be severely damaged by corrosion.
Maximum protection against freezing is provided
with a 68 percent antifreeze concentration, which
prevents freezing down to -67.7 deg. C (-90 deg. F). A
higher percentage will freeze at a warmer tempera-
ture. Also, a higher percentage of antifreeze can
cause the engine to overheat because the specific
heat of antifreeze is lower than that of water.
100 Percent Ethylene-Glycol—Should Not Be Used in
DaimlerChrysler Corporation Vehicles
Use of 100 percent ethylene-glycol will cause for-
mation of additive deposits in the system, as the cor-
rosion inhibitive additives in ethylene-glycol require
the presence of water to dissolve. The deposits act as
insulation, causing temperatures to rise to as high as
149 deg. C (300) deg. F). This temperature is hot
enough to melt plastic and soften solder. The
increased temperature can result in engine detona-
tion. In addition, 100 percent ethylene-glycol freezes
at 22 deg. C (-8 deg. F ).
Propylene-glycol Formulations—Should Not Be Used in
DaimlerChrysler Corporation Vehicles
Propylene-glycol formulations do not meet
Chrysler coolant specifications.
It’s overall effec-
tive temperature range is smaller than that of ethyl-
ene-glycol. The freeze point of 50/50 propylene-glycol
and water is -32 deg. C (-26 deg. F). 5 deg. C higher
than ethylene-glycol’s freeze point. The boiling point
(protection against summer boil-over) of propylene-
glycol is 125 deg. C (257 deg.F)at96.5 kPa (14 psi),
compared to 128 deg. C (263 deg. F) for ethylene-gly-
col. Use of propylene-glycol can result in boil-over or
freeze-up in Chrysler vehicles, which are designed for
ethylene-glycol. Propylene glycol also has poorer heat
transfer characteristics than ethylene glycol. This
can increase cylinder head temperatures under cer-
tain conditions.
Fig. 5 Coolant Tank Pressure/Vent Cap
1 – RELEASE PRESSURE
2 – CAP COVER
3 – SPRING
4 – GASKET
5 – RUBBER VACUUM VALVE
6 – PRESSURE VALVE
between the closed cooling system and the atmo-
sphere. If the vacuum valve is stuck shut, the radia-
tor and/or cooling system hoses will collapse on cool-
down.
Propylene-glycol/Ethylene-glycol Mixtures—Should Not Be
Used in DaimlerChrysler Corporation Vehicles
Propylene-glycol/ethylene-glycol Mixtures can
cause the destabilization of various corrosion inhibi-
tors, causing damage to the various cooling system
components. Also, once ethylene-glycol and propy-
lene-glycol based coolants are mixed in the vehicle,
conventional methods of determining freeze point will
not be accurate. Both the refractive index and spe-
cific gravity differ between ethylene glycol and propy-
lene glycol.
NOTE: Do not use any type of tool when tightening
the cap. Hand tighten only.
COOLANT PERFORMANCE
DESCRIPTION
The required ethylene-glycol (antifreeze) and water
mixture depends upon the climate and vehicle oper-
ating conditions. The recommended mixture of 50/50
ethylene-glycol and water will provide protection
against freezing to -37 deg. C (-35 deg. F). The anti-
freeze concentration
must always
be a minimum of
44 percent, year-round in all climates.
If percentage
is lower than 44 percent, engine parts may be
eroded by cavitation, and cooling system com-
COOLING SYSTEM HOSES
DESCRIPTION
Rubber hoses route coolant to and from the radia-
tor, and heater core.
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