OPERATION
Coolant flows through the engine block absorbing the heat from the engine, then flows to the radiator where the cooling fins in the radiator transfers the heat from the coolant to the atmosphere. During cold weather the ethylene-glycol or propylene-glycol coolant prevents water present in the cooling system from freezing within temperatures indicated by mixture ratio of coolant to water.
DESCRIPTION
This 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.
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.
The coolant reservoir/overflow system has a radiator mounted pressurized cap, an overflow tube, and a plastic coolant reservoir/overflow tank, mounted to the right side of the cowl. It is mounted to the cowl with two nuts on top, and a slide bracket on the bottom.
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.
Scheme 5
- Disconnect the hose from radiator filler neck.
- Remove coolant recovery bottle.
| CAUTION | The power cord must be secured in its retainer clips, and not positioned so it could contact linkages or exhaust manifolds and become damaged. |
The block heater is operated by ordinary house current (110 Volt A.C.) through a power cord and connector located in the engine compartment. The heater is mounted in a core hole (in place of a core hole plug) in the engine block, with the heating element immersed in coolant.
The block heater element is submerged in the cooling system's coolant. When electrical power (110 volt A.C.) is applied to the element, it creates heat. This heat is transferred to the engine coolant. This provides easier engine starting and faster warm-up when vehicle is operated in areas having extremely low temperatures.
The Engine Coolant Temperature (ECT) sensor is used to sense engine coolant temperature. The sensor protrudes into an engine water jacket.
The ECT sensor is a two-wire Negative Thermal Coefficient (NTC) sensor. Meaning, as engine coolant temperature increases, resistance (voltage) in the sensor decreases. As temperature decreases, resistance (voltage) in the sensor increases.
At key-on, the Powertrain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor. The PCM then monitors the signal as it passes through the ECT sensor to the sensor ground (sensor return).
When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.
The PCM uses inputs from the ECT sensor for the following calculations
- for engine coolant temperature gauge operation through CCD or PCI (J1850) communications
- Injector pulse-width
- Spark-advance curves
- ASD relay shut-down times
- Idle Air Control (IAC) motor key-on steps
- Pulse-width prime-shot during cranking
- O2 sensor closed loop times
- Purge solenoid on/off times
- EGR solenoid on/off times (if equipped)
- Leak Detection Pump operation (if equipped)
- Radiator fan relay on/off times (if equipped)
- Target idle speed
DESCRIPTION - 3.7L ENGINE
| 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 195°F (90°C). Above this temperature, coolant is allowed to flow to the radiator. This provides quick engine warm up and overall temperature control. On the 3.7L engine the thermostat is designed to block the flow of the coolant bypass journal by 50% instead of completely blocking the flow. This design controls coolant temperature more accurately.
Scheme 6
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: longer engine warmup time, unreliable warmup performance, increased exhaust emissions and crankcase condensation. This condensation can result in sludge formation.
The wax pellet is located in a sealed container at the spring end of the thermostat. When heated, the pellet expands, overcoming closing spring tension and water pump pressure to force the valve to open.
| CAUTION | Engines equipped with serpentine 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-fluid-filled coupling used to connect the fan blades to 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 pre-determined maximum level at higher engine speeds.
Scheme 7
A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit (a typical viscous unit is shown. 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.
Scheme 8
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.
All vehicles are equipped with a cross flow type radiator with plastic side tanks.
Scheme 9
Plastic tanks, while stronger than brass, are subject to damage by impact, such as from tools or wrenches. Handle radiator with care.
The cooling system cap is located on the coolant pressure bottle. The cap construction includes; stainless steel swivel top, rubber seals and retainer, main spring, and a spring loaded valve.
Scheme 10
| CAUTION | Use only the pressure cap specified for this vehicle. Use of other pressure caps can lead to coolant loss and overheating. |
The pressure cap allows the cooling system to operate at higher than atmospheric pressure which raises the coolant boiling point, thus allowing increased radiator cooling capacity. The pressure cap releases pressure at some point within a range of 110 kPa +/- 14 kPa (16 psi +/- 2 psi).
A spring-loaded vent valve in the center of the cap allows the system to pressurize and depressurize 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.
The fan is electrically controlled by the powertrain control module (PCM) through the fan control relay. This relay is located on the left wheel house in the engine compartment.
Scheme 11
The electric radiator cooling fan is controlled by the Powertrain Control Module (PCM) through the radiator cooling fan relay. The PCM regulates fan operation based on input from the engine coolant temperature sensor, battery temperature sensor, air conditioning select switch and vehicle speed.
The fan is not energized during engine cranking regardless of the electrical input from the temperature sensors and, air conditioning switch. However, if engine operation conditions warrant fan engagement, the fan will run once engine starts.
On vehicles NOT equipped with AC: The relay is energized when the coolant temperature is above 80° C (176° F), or battery temperature sensor above - 12° C (10° F). It will then de-energize when coolant temperature drops below 82° C (180° F), or batter temperature sensor below - 9° C (16° F).
Vehicles Equipped with AC: In addition to using coolant temperature and battery temperature sensor to control cooling fan operation, the cooling fan will also be engaged when the, air conditioning system is activated. The relay is also energized when, air conditioning is selected and coolant temperature is above 95° C (203° F), or, air conditioning is selected and battery temperature sensor is above 41° C (106° F). It will then de-energize when, air conditioning is selected and coolant temperature is below 92° C (198° F), or, air conditioning is selected and battery temperature is below 38° C (100° F).
| CAUTION | If the viscous fan drive is replaced because of mechanical damage, the cooling fan blades should also be inspected. Inspect for fatigue cracks, loose blades, or loose rivets that could have resulted from excessive vibration. Replace fan blade assembly if any of these conditions are found. Also inspect water pump bearing and shaft assembly for any related damage due to a viscous fan drive malfunction. |
The thermal viscous fan drive is a silicone-fluid-filled coupling used to connect the fan blades to 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.
Scheme 12
On the 3.7L engine, an electric fan is standard and the viscous fan is added on for trailer tow packages only.
A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit. 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. Normally less than three hundred (300) RPM.
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.
The water pump has a cast aluminum body and housing with a stamped steel impeller. The water pump bolts directly to the block. The cylinder block to water pump seal is provided by a rubber O-ring. The water pump is driven by the engine timing belt.
Scheme 13
The water pump is the heart of the cooling system. The coolant is pumped through the engine block, cylinder head, heater core, and radiator.
Scheme 14
- Disconnect negative cable from battery.
- Raise vehicle on a hoist.
- Remove the accessory drive belts. See «ACCESSORY DRIVE»(ref-176720-S40917373212005051000000) .
- Remove the belt tensioner.
- Drain the cooling system. See «DRAINING COOLING SYSTEM»(ref-176720-S21443309012005051000000) .
- Remove the generator.
- Remove the power steering pump.
- Remove the A/C compressor.
- Remove the accessory drive bracket.
- Remove the timing belt. See ENGINE MECHANICAL article.
- Remove timing belt idler pulley.
- Hold camshaft sprocket with Special tool C-4687 and adaptor C-4687-1 while removing bolt. Remove both cam sprockets.
- Remove the timing belt rear cover.
- Remove water pump to engine attaching screws.
DESCRIPTION - WATER PUMP
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 single serpentine drive belt.
The water pump impeller is pressed onto the rear of a shaft that rotates in bearings pressed into the housing. The housing has two small holes to allow seepage to escape. The water pump seals are lubricated by the antifreeze in the coolant mixture. No additional lubrication is necessary.
Both heater hoses are connected to fittings on the timing chain front cover. The water pump is also mounted directly to the timing chain cover and is equipped with a non serviceable integral pulley.
Scheme 15
DESCRIPTION - WATER PUMP BYPASS
The 3.7L engine uses an internal water/coolant bypass system. The design uses galleries in the timing chain cover to circulate coolant during engine warm-up preventing the coolant from flowing through the radiator. The thermostat uses a stub shaft located at the rear of the thermostat to control flow through the bypass gallery.
OPERATION - WATER PUMP
A centrifugal water pump circulates coolant through the water jackets, passages, intake manifold, radiator core, cooling system hoses and heater core, this coolant absorbs the heat generated when the engine is running. The pump is driven by the engine crankshaft via a drive belt.
An internal high capacity/high efficiency cooler is used on all vehicles, these coolers are an oil-to-coolant type, which consists of plates mounted in the radiator outlet tank. Because the internal oil cooler is so efficient, no auxiliary oil cooler is offered. The cooler is not serviceable separately from the radiator.