Cooling System: Description and Operation
COOLING SYSTEMThe cooling system consists of an engine cooling module, pressure cap, coolant bottle, thermostat (inlet), coolant, plumbing, and a water pump to circulate the coolant. The engine cooling module consist of a radiator, electric fan motors, shroud, internal transmission oil cooler, internal engine oil cooler (if equipped), air conditioning condenser, and a auxiliary transmission oil cooler (if equipped).
^ When Engine is cold: Thermostat is closed, cooling system has no flow through the radiator. The coolant flows through the engine heater core, coolant bottle and an internal engine by-pass.
^ When Engine is warm: Thermostat is open, coolant flows through the radiator, heater core, coolant bottle and by-pass (no by-pass 2.7L).
The cooling systems 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 coolant for heater, and cooling for automatic transmission fluid. 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.
The coolant flow circuit is shown.
ACCESSORY DRIVE BELTS
The accessory drive system on 2.7L and 3.2/3.5L engines utilizes two different belts. A conventional V-belt drives the air conditioning compressor on 3.2/3.5L engines, Poly-V belt on the 2.7L engine. The generator and power steering pump on all engines, are driven by a Poly-V belt.
COOLANT BOTTLE
The coolant bottle consists of two chambers. The pressure chamber keeps the coolant free of trapped air, provides a volume for expansion and contraction, and provides a convenient and safe method for checking and adjusting coolant level at atmospheric pressure. It also provides some reserve coolant to cover minor leaks, evaporation or boiling losses. The overflow chamber allows coolant recovery in case of an overheat. An overflow hose connects the pressure chamber to the overflow chamber.
NOTE: Coolant will normally be in the pressure chamber side of the coolant bottle. The overflow chamber should normally be empty.
ENGINE THERMOSTAT
The thermostat on the 2.7L and 3.2/3.5L engines are located on the lower left side of engine, near the front. The thermostat on both engines are on the inlet side of the water pump. The thermostats have an air bleed located in the thermostat flange.
WATER PUMP
WATER PUMP-2.7L ENGINE
The 2.7L pump has a die cast aluminum body and a plastic swept vane impeller. It bolts directly to the cylinder block, behind the timing chain cover. The water pump is driven by the back side of the engine primary timing chain.
WATER PUMP-3.2/3.5L ENGINE
The 3.2/3.5L water pump has a plastic swept vane impeller. The housing bolts directly to the right rear timing belt cover, using an O-ring gasket for pump to cover sealing. The pump is driven by the engine timing belt.
COOLANT
CAUTION: Use of Propylene Glycol based coolants is not recommended, as they provide less freeze protection and less corrosion protection.
The cooling system is designed around the coolant. The coolant must accept heat from engine metal, in the cylinder head area near the exhaust valves and engine block. Then carry this heat to the radiator where the tube/fin radiator can give it up to the air.
The use of aluminum cylinder blocks, cylinder heads, and water pumps requires special corrosion protection. Mopar (R) Antifreeze/Coolant, 5 Year/100,000 Mile Formula (orange in color), or the equivalent ethylene glycol base coolant with corrosion inhibitors (called OAT, for Organic Additive Technology) is recommended. This coolant offers the best engine cooling without corrosion when mixed to a freeze point of -37°C (-35°F) to -59°C (-50°F). If it loses color or becomes contaminated, drain, flush, and replace with fresh properly mixed solution.
WARNING: ANTIFREEZE IS AN ETHYLENE GLYCOL BASE COOLANT AND IS HARMFUL IF SWALLOWED OR INHALED. IF SWALLOWED, DRINK TWO GLASSES OF WATER AND INDUCE VOMITING. IF INHALED, MOVE TO FRESH AIR AREA. SEEK MEDICAL ATTENTION IMMEDIATELY. DO NOT STORE IN OPEN OR UNMARKED CONTAINERS. WASH SKIN AND CLOTHING THOROUGHLY AFTER COMING IN CONTACT WITH ETHYLENE GLYCOL. KEEP OUT OF REACH OF CHILDREN. DISPOSE OF GLYCOL BASE COOLANT PROPERLY, CONTACT YOUR DEALER OR GOVERNMENT AGENCY FOR LOCATION OF COLLECTION CENTER IN YOUR AREA. DO NOT OPEN A COOLING SYSTEM WHEN THE ENGINE IS AT OPERATING TEMPERATURE OR HOT UNDER PRESSURE, PERSONAL INJURY CAN RESULT. AVOID RADIATOR COOLING FAN WHEN ENGINE COMPARTMENT RELATED SERVICE IS PERFORMED, PERSONAL INJURY CAN RESULT.
RADIATOR
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 than brass, are subject to damage by impact, such as wrenches, or heat from torch.
COOLANT PRESSURE BOTTLE CAP
The Coolant bottle is equipped with a pressure cap which releases pressure at some point within a range of 110 kPa ±14 kPa (16 psi ±2 psi).
The system will operate at higher than atmospheric pressure, which raises the coolant boiling point, thus allowing increased radiator cooling capacity.
There is a spring-loaded vent valve in the center of the cap that allows the system to pressurize and repressurize without creating a vacuum. If the valve is stuck open, coolant will escape to the overflow hose. There is also a gasket in the cap to seal to the top of the filler neck.
CAUTION: Use only the pressure cap specified for this vehicle. Use of other pressure caps can lead to coolant loss and overheating.
DUAL FAN MODULE
All models use electric motor driven fans. The fan modules include a motor support and shroud. The module is fastened to the radiator by screws with square nuts and retaining clips.
The dual fan module is a combination of 2 fans mounted in an one piece shroud which operate at two speeds and are simultaneously activated. The dual fan system improves engine cooling and air conditioning performance in hot weather and severe driving conditions, while reducing fan noise and power consumption. Attempts to reduce high temperature gauge reading by increasing engine speed, can increase high temperature.
FAN SHROUD
All vehicles have fan shrouds to improve fan air flow efficiency. The shroud supports the electric fan motor and fan.
AUTOMATIC TRANSMISSION OIL COOLER
The transmission oil cooler circuit consists of a series connected internal cooler mounted inside the left radiator tank and an auxiliary external oil cooler mounted to the front of the air conditioning condenser.
Steel tubes and rubber lines supply the oil from the transmission to the internal oil cooler and return the oil to the transmission from the auxiliary external oil cooler.
Use only approved transmission oil cooler hoses. Since these hoses are molded to fit space available, molded hoses are required. The steel tubes must be flared to ensure sealing of the hose. Torque oil cooler hose clamps to 2 Nm (18 in. lbs.). Torque cooler line flare nuts at transmission to 30 Nm (260 in. lbs.).
ENGINE OIL COOLER-3.2/3.5L
The 3.2/3.5L engine uses an engine oil cooler that is mounted inside the right radiator tank. An oil cooler pressure control valve is used to control flow to the cooler. Engine oil travels from the control valve through the supply line and into the cooler. The engine oil exits the cooler through the oil return line and is returned to the engine oil pan.
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 grill. This provides easier engine starting and faster warm-up when the vehicle is operated in areas having extremely low temperatures.