Jeep Cherokee (XJ): Description and operation

Cooling system

DESCRIPTION

The cooling system regulates engine operating temperature.

It allows the engine to reach normal operating temperature as quickly as possible, maintains normal operating temperature and prevents overheating.

The cooling system also provides a means of heating the passenger compartment and cooling the automatic transmission fluid (if equipped). The cooling system is pressurized and uses a centrifugal water pump to circulate coolant throughout the system.

An optional factory installed heavy duty cooling package is available on most models. The package consists of a radiator that has an increased number of cooling fins. Vehicles equipped with a 2.5L/4.0L engine and heavy duty cooling and/or air conditioning also have an auxiliary electric cooling fan.

The cooling system consists of:

•  A radiator
•  Cooling fan (mechanical and/or electrical)
•  Thermal viscous fan drive
• Fan shroud
•  Radiator pressure cap
•  Thermostat
•  Coolant reserve/overflow system
•  Transmission oil cooler (if equipped with an automatic transmission)
•  Coolant
•  Water pump
•  Hoses and hose clamps

Cooling system circulation for 2.5L/4.0L models is shown in (Fig. 1).

Fig. 1 Coolant Circulation-2.5L/4.0L Engines

1 - HEATER CORE
2 - TO COOLANT RESERVE/OVERFLOW TANK
3 - THERMOSTAT HOUSING
4 - RADIATOR
5 - WATER PUMP

Automatic transmission oil cooler

DESCRIPTION

All models equipped with an automatic transmission are equipped with a transmission oil cooler mounted internally within the radiator tank. This internal cooler is supplied as standard equipment on all models equipped with an automatic transmission.

Transmission oil is cooled when it passes through this separate cooler. In case of a leak in the internal radiator mounted transmission oil cooler, engine coolant may become mixed with transmission fluid or transmission fluid may enter engine cooling system.

Both cooling system and transmission should be drained and inspected if the internal radiator mounted transmission cooler is leaking.

An auxiliary air-to-oil transmission oil cooler is available with most engine packages.

The auxiliary air-to-oil transmission oil cooler is located in front of the radiator or A/C condenser (if equipped) and behind the grill. It is mounted to the front frame crossmember.

The auxiliary oil coolers on all models operate in conjunction with the internal radiator mounted main oil cooler. The transmission oil is routed through the main cooler first, then the auxiliary cooler, before returning to the transmission.

Fig. 2 Auxiliary Transmission Oil Cooler

1 - AUXILIARY TRANSMISSION OIL COOLER

Coolant reserve/overflow system

DESCRIPTION

The system works along with the radiator pressure cap. This is done by using thermal expansion and contraction of the coolant to keep the coolant free of trapped air. It provides:

•  A volume for coolant expansion and contraction.
•  A convenient and safe method for checking/adjusting coolant level at atmospheric pressure. This is done without removing the radiator pressure cap.
•  Some reserve coolant to the radiator to cover minor leaks and evaporation or boiling losses.

The coolant reserve/overflow system consists of a radiator mounted pressurized cap, a plastic reserve/ overflow tank (Fig. 3) (Fig. 4), a tube (hose) connecting the radiator and tank, and an overflow tube on the side of the tank.

Fig. 3 Reserve/Overflow Tank-Except Right Hand Drive

1 - COOLANT RESERVE/OVERFLOW TANK
2 - CLAMP
3 - MOUNTING BOLTS
4 - TUBE TO RADIATOR

OPERATION

As the engine cools, a vacuum is formed in the cooling system of both the radiator and engine. Coolant will then be drawn from the coolant tank and returned to a proper level in the radiator.

Cooling system fans

DESCRIPTION

All models are equipped with a viscous fan. This thermal viscous fan drive is a torque-and-temperature- sensitive clutch unit. It automatically increases or decreases fan speed to provide proper engine cooling.

Vehicles with a 2.5L/4.0L engine with air conditioning, or 4.0L with "max" cooling also have an auxiliary electrical cooling fan.

Fig. 4 Reserve/Overflow Tank-With Right Hand Drive

1 - CLAMP
2 - COOLANT RESERVE/OVERFLOW TANK
3 - MOUNTING BOLTS
4 - LOWER BRACKET
5 - TUBE TO RADIATOR

Fig. 5 Viscous Fan Drive and Fan Blade Assembly

1 - VISCOUS FAN DRIVE
2 - FAN BLADE ASSEMBLY

Block heater

DESCRIPTION

WARNING: DO NOT OPERATE ENGINE UNLESS BLOCK HEATER CORD HAS BEEN DISCONNECTED FROM POWER SOURCE AND SECURED IN PLACE.

An optional engine block heater is available for all models. The heater is equipped with a power cord.

The cord is attached to an engine compartment component with tie-straps. The heater warms the engine providing easier engine starting and faster warm-up in low temperatures. The heater is mounted in a core hole of the engine cylinder block (in place of a freeze plug) with the heating element immersed in engine coolant.

BLOCK HEATER SPECIFICATIONS

•  2.5L 4-Cylinder Engine: 115 Volts 400 Watts
•  4.0L 6-Cylinder Engine: 120 Volts 600 Watts

Fig. 6 Engine Block Heater

1 - BLOCK HEATER
2 - CYLINDER BLOCK
3 - BLOCK HEATER POWER CORD

OPERATION

Connecting the power cord to a grounded 110-120 volt AC electrical outlet with a grounded, three-wire extension cord activates the block heater.

Thermostat

DESCRIPTION

CAUTION: Do not operate an engine without a thermostat, except for servicing or testing.

A pellet-type thermostat controls the operating temperature of the engine by controlling the amount of coolant flow to the radiator. On all engines the thermostat is closed below 195F (90C). Above this temperature, coolant is allowed to flow to the radiator.

This provides quick engine warm-up and overall temperature control.

An arrow plus the word UP is stamped on the front flange next to the air bleed. The words TO RAD are stamped on one arm of the thermostat.

They indicate the proper installed position.

The same thermostat is used for winter and summer seasons. An engine should not be operated without a thermostat, except for servicing or testing.

Operating without a thermostat causes other problems.

These are: A 'check engine' light and a DTC will eventually be set, longer engine warm-up time, unreliable warm-up performance, increased exhaust emissions and crankcase condensation. This condensation can result in sludge formation.

Fig. 7 Thermostat and Housing

1 - LONG BOLT
2 - GASKET
3 - THERMOSTAT
4 - THERMOSTAT HOUSING
5 - SHORT BOLT

Radiator

DESCRIPTION

CAUTION: Plastic tanks, while stronger than brass, are subject to damage by impact, such as wrenches.

Radiators for both engines are the cross flow type.

Plastic tanks are used on all radiators.

Fig. 8 Cross Flow Radiator

1 - RADIATOR

Radiator pressure cap

DESCRIPTION

All radiators are equipped with a pressure cap.

This cap releases pressure at some point within a range of 83-110 kPa (12-16 psi). The pressure relief point (in pounds) is engraved on top of the cap (Fig.

9).

The cooling system will operate at pressures slightly above atmospheric pressure. This results in a higher coolant boiling point allowing increased radiator cooling capacity. The cap contains a springloaded pressure relief valve that opens when system pressure reaches release range of 83-110 kPa (12-16 psi).

A rubber gasket seals radiator filler neck. This is done to maintain vacuum during coolant cool-down and to prevent leakage when system is under pressure

Fig. 9 Radiator Pressure Cap and Filler Neck-Typical

1 - FILLER NECK SEAL
2 - VACUUM VENT VALVE
3 - PRESSURE RATING
4 - PRESSURE VALVE

OPERATION

A vent valve in the center of cap allows a small coolant flow through cap when coolant is below boiling temperature. The valve is completely closed when boiling point is reached. As the coolant cools, it contracts and creates a vacuum in the cooling system.

This causes the vacuum valve to open and coolant in the reserve/overflow tank to be drawn through its connecting hose into radiator. If the vacuum valve is stuck shut, the radiator hoses will collapse on cooldown.

Water pump

DESCRIPTION

CAUTION: All engines are equipped with a reverse (counter-clockwise) rotating water pump and viscous fan drive assembly. REVERSE is stamped or imprinted on the cover of the viscous fan drive and inner side of the fan. The letter R is stamped into the back of the water pump impeller (Fig. 10).

A centrifugal water pump circulates coolant through the water jackets, passages, intake manifold, radiator core, cooling system hoses and heater core.

The pump is driven from the engine crankshaft by a drive belt on all engines.

The water pump impeller is pressed onto the rear of a shaft that rotates in bearings pressed into the housing. The housing has a small hole to allow seepage to escape. The water pump seals are lubricated by the antifreeze in the coolant mixture. No additional lubrication is necessary.

Fig. 10 Reverse Rotating Water Pump-Typical

1 - R STAMPED INTO IMPELLER

Hose clamps

DESCRIPTION

The cooling system utilizes both worm drive and spring type hose clamps. If a spring type clamp replacement is necessary, replace with the original Mopart equipment spring type clamp.

CAUTION: A number or letter is stamped into the tongue of constant tension clamps. If replacement is necessary, use only a original equipment clamp with matching number or letter (Fig. 11).

Fig. 11 Spring Clamp Size Location

1 - SPRING CLAMP SIZE LOCATION

OPERATION

The worm type hose clamp uses a specified torque value to maintain proper tension on a hose connection.

The spring type hose clamp applies constant tension on a hose connection. To remove a spring type hose clamp, use Special Tool 6094 or equivalent, constant tension clamp pliers (Fig. 12) to compress the  hose clamp.

Fig. 12 Hose Clamp Tool

1 - HOSE CLAMP TOOL 6094
2 - HOSE CLAMP

Viscous fan drive

DESCRIPTION

CAUTION: Engines equipped with poly-V drive belts have reverse rotating fans and viscous fan drives. They are marked with the word REVERSE to designate their usage. Installation of the wrong fan or viscous fan drive can result in engine overheating.

The thermal viscous fan drive is a silicone-fluidfilled coupling used to connect the fan blades to either the engine or the water pump shaft. The coupling allows the fan to be driven in a normal manner.

This is done at low engine speeds while limiting the top speed of the fan to a predetermined maximum level at higher engine speeds.

2.5L vehicles with A/C are equipped with a viscous fan drive which is designed to "free wheel" during most of the ambient conditions encountered by the vehicle and will only engage during high heat loads as seen in trailer towing or high ambient temperatures.

A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit. A typical viscous unit is shown in (Fig. 13). This spring coil reacts to the temperature of the radiator discharge air. It engages the viscous fan drive for higher fan speed if the air temperature from the radiator rises above a certain point. Until additional engine cooling is necessary, the fan will remain at a reduced rpm regardless of engine speed.

Vehicles equipped with 2.5L engines have what is know as an hybrid cooling fan system. This means that not only do they have a viscous fan but they also have an electric fan as well. The hybrid viscous fan drive has a low speed characteristic. This causes the mechanical fan speeds to be very low 200-400 rpm range when not engaged allowing the engine to have additional performance and horsepower gaines.

Fig. 13 Typical Viscous Fan Drive

1 - VISCOUS FAN DRIVE
2 - MOUNTING HUB
3 - THERMOSTATIC SPRING

OPERATION

Only when sufficient heat is present, will the viscous fan drive engage. This is when the air flowing through the radiator core causes a reaction to the bimetallic coil. It then increases fan speed to provide the necessary additional engine cooling.

Once the engine has cooled, the radiator discharge temperature will drop. The bimetallic coil again reacts and the fan speed is reduced to the previous disengaged speed.

Electric cooling fan

DESCRIPTION

Vehicles equipped with a 2.5L/4.0L engine and air conditioning and 4.0L vehicles equipped with the "max" cooling package also have an electrical cooling fan. The fan is controlled by the cooling fan relay, which is located in the power distribution center (PDC) (Fig. 15). For the location of relay within the PDC, refer to the label on PDC cover.

The electric fan on the 2.5L engine equipped vehicles is considered the primary fan (low to moderate ambient conditions) and is energized when the JTEC receives input from the coolant temperature sensor or the a/c system and supplies ground to the cooling fan relay.

The cooling fan motor is protected by a 40 amp maxi-fuse located in the PDC. The fan relay is protected by a 15 amp fuse located in the junction block.

OPERATION

Electric cooling fan 2.5L: When air conditioning is not requested, the electric fan will not come on unless the coolant temperature is at least 103 C (218 F), at which time the fan will come on and remain on until the coolant temperature drops to 99 C (210 F) or below. When air conditioning is requested (including defroster operation), the fan will cycle on and off in conjunction with the A/C compressor unless the coolant temperature is at least 97 C (207 F), at which time the fan will come on and remain on until the coolant temperature drops to 93 C (199 F) or below. Then, the cycle fan operation will resume. When the fan is scheduled to be on, the powertrain control module (PCM) provides a ground path for the fan relay. This ground is provided to the cooling fan relay through pin C2 of PCM connector C3. Battery voltage is then applied to the fan through the relay. When the fan is scheduled to be off, the PCM opens the ground path to the relay. This will prevent the cooling fan from being energized.

Fig. 14 Electric Cooling Fan

1 - (LHD)
2 - (RHD)
3 - VISCOUS FAN SHROUD
4 - ELECTRIC FAN MODULE
5 - ISOLATOR
6 - RADIATOR
7 - LOWER CROSSMEMBER
8 - U-NUT
9 - UPPER CROSSMEMBER

Fig. 15 Power Distribution Center (PDC)

1 - RIGHT FENDER
2 - BATTERY
3 - POWER DISTRIBUTION CENTER

Electric cooling fan 4.0L: With or without A/C request the electric fan will come on only when the coolant temperature is at least 106 C (223 F), and will remain on until the coolant temperature drops to 103 C (217 F) or below. Regardless of coolant temperature, When air conditioning system pressures reach 2068.5 6 138 kPa (300 6 20 psi) the electric fan will engage and continue to run until the A/C system pressure drops to 1620.3 kPa (235 psi) minimum, then the electric fan will shut off.