Cooling System: Description and Operation
COOLING SYSTEMThroughout this group, references may be made to a particular vehicle by letter or number designation.
The cooling system consists of an engine cooling module, thermostat, coolant, a water pump to circulate the coolant. The engine cooling module may consist of a radiator, electric fan motor, shroud, radiator pressure cap, coolant reserve system, transmission oil cooler, hoses, clamps, air condition condenser, transmission oil lines and charge air cooler.
- When Engine is cold: Thermostat is closed, cooling system has no flow through the radiator. The coolant bypass flows through the engine and heater core.
- When Engine is warm: Thermostat is open, cooling system has bypass flow and coolant flow through radiator and heater core.
Its primary purpose is to maintain engine temperature in a range that will provide satisfactory engine performance and emission levels under all expected driving conditions. It also provides hot water (coolant) for heater performance and cooling for automatic transmission oil. It does this by transferring heat from engine metal to coolant, moving this heated coolant to the radiator, and then transferring this heat to the ambient air.
Figure 1 Cooling System Operation 2.4L Engine:
Figure 2 Cooling System Operation 2.5L Engine:
Coolant flow circuits for 2.4L engine equipped vehicles are shown. The 2.5L engine coolant routing is shown.
WATER PIPES-2.5L
The 2.5L engine use metal piping beyond the lower radiator hose to route coolant to the suction side of water pump, located in the V of the cylinder banks.
Figure 3, Engine Inlet Coolant Pipes:
The pipes are also provided with inlet nipples for thermostat bypass, heater return coolant hoses, and brackets for rigid engine attachment. The pipes employ O-rings for sealing at their interconnection and to the water pump.
ACCESSORY DRIVE BELTS
Figure 4, Drive Belts - 2.4L Engine:
Figure 5:
The engines are equipped with 2 accessory drive belts. One belt drives the power steering pump, the other drives the generator and air conditioning.
COOLANT RECOVERY SYSTEM (CRS)
Figure 6, Coolant Recovery System:
This system works in conjunction with the pressure cap to utilize thermal expansion and contraction of the coolant to keep the coolant free of trapped air. It provides a volume for expansion and contraction, provides a convenient and safe method for checking coolant level, and adjusting level at atmospheric pressure without removing the pressure cap. It also provides some reserve coolant to cover minor leaks and evaporation or boiling losses. All vehicles are equipped with this system.
See Coolant Level Check Service, Deaeration and Pressure Cap procedures for operation and service.
ENGINE THERMOSTATS
Figure 7:
The 2.4L engine thermostat is located on the front of the engine (radiator side) in the thermostat housing engine outlet connector. The thermostat has a air bleed located in the flange and a O-ring with a locating dimple incorporate on it. There is a relief in the cylinder head for locating the air bleed.
Figure 8:
The 2.5L engine thermostat is located in a thermostat housing, located below the throttle body. This thermostat has an air bleed valve, located in the thermostat flange.
WATER PUMP-2.0/2.4L ENGINES
The water pump body is made of aluminum with a steel impeller. The water pump is bolted to the front of the block, and driven by the timing belt. The water pump is the heart of the cooling system, pumping the coolant through the engine block, cylinder head, heater core, and radiator.
NOTE: The water pump on all models can be replaced without discharging the air conditioning system.
WATER PUMP-2.5L ENGINE
Figure 9:
The 2.5L pump bolts directly to the engine block uses a gasket for pump to block sealing. The pump is serviced as an assembly.
The water pump is driven by the timing belt. See Engine, Timing Components, Timing Belt for component removal providing access to water pump.
WATER PUMP INLET TUBE-2.4L ENGINE
The inlet tube connects the water pump to the radiator and heater core. This tube is sealed by a O-ring and held in place by fasteners to the block.
COOLANT
The cooling system is designed around the coolant. The coolant must accept heat from engine block metal and in the cylinder head area near the exhaust valves. Then coolant carries this heat to the radiator where the tube/fin assemblies of these components can give off the heat to the air.
Mopar(R) Antifreeze or the equivalent is recommended for optimum cooling performance and corrosion protection when mixed to a freeze point of -37° C ( 35° F).
COOLANT REPLACEMENT
Refer to Maintenance for schedule.
COOLING SYSTEM PRESSURE CAP
Figure 10:
The cooling system is equipped with a pressure cap that releases pressure at some point within a range of 97-124 kPa (14-18 psi).
The system will operate at higher than atmospheric pressure, which raises the coolant boiling point, allowing increased radiator cooling capacity.
There is a vent valve in the center of the cap that allows a small coolant flow to the CRS tank. If the valve is stuck shut, the radiator hoses will collapse on cool-down. Clean the vent valve to ensure proper sealing when boiling point is reached.
There is a gasket in the cap that seals to the top of the filler neck so that vacuum is maintained to draw coolant back into the system from the coolant reserve system tank.
RADIATOR
Figure 11:
The radiators are cross flow types (horizontal tubes) with design features that provide greater strength as well as sufficient heat transfer capabilities to keep the engine satisfactorily cooled.
CAUTION: Plastic tanks, while stronger then brass, are subject to damage by impact, such as wrenches.
COOLING SYSTEM FAN
Figure 11:
The radiator has a single cooling fan, with a two speed motor. The fan is controlled by the Powertrain Control Module (PCM) which energizes the fan relay.
AUTOMATIC TRANSMISSION OIL COOLER
Figure 11:
Oil coolers are internal oil to coolant type, mounted in the radiator left tank. Rubber oil lines feed the oil cooler and the automatic transmission. Use only approved transmission oil cooler hose. Since these are molded to fit space available, molded hoses are recommended. Tighten Oil Cooler Hose Clamps to 2 Nm (18 inch lbs.).
EXTERNAL TRANSMISSION OIL COOLER
Figure 12:
Figure 13, External Transmission Oil Cooler - 2.5L Engine:
An external oil-to-air type transmission oil cooler is mounted ahead of the cooling module. This style of cooler uses steel tubes and rubber oil lines to feed oil from the internal (in radiator tank) cooler to the external cooler and then to the automatic transmission. Use only approved transmission oil cooler hose. Since these hoses are molded to fit space available, replacement molded hoses are recommended.
ENGINE BLOCK HEATER
On all models an engine block heater is available as an optional accessory. The heater, operated by ordinary house current (110 Volt A.C.) through a power cord and connector behind the radiator grille.