The cooling system's function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the system cools slowly or not at all. This allows the engine to warm quickly.

Cooling Cycle

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. Some coolant will then be pumped from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost.

Coolant is also pumped through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

Coolant is also directed to the throttle body. There it circulates through passages in the casting. During initial start-up, the coolant assists in warming the throttle body. During normal operating temperatures, the coolant assists in keeping the throttle body cool.

From the cylinder heads, the coolant is then forced to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine is warmed, or it will flow through the thermostat and into the radiator where it is cooled and the coolant cycle is completed.

Operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components:

Coolant

The engine coolant is a solution made up of a 50-50 mixture of DEX-COOL and clean drinkable water. The coolant solution carries excess heat away from the engine to the radiator, where the heat is dissipated to the atmosphere.

Radiator

The radiator is a heat exchanger. It consists of a core and 2 tanks. The aluminum core is a crossflow tube and fin design. This is a series of tubes that extend side to side from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer from the coolant to the atmosphere. The inlet and outlet tanks are molded with a high temperature, nylon reinforced plastic. A high temperature rubber gasket seals the tank flange edge. The tanks are clamped to the core with clinch tabs. The tabs are part of the aluminum header at each end of the core.

The radiator removes heat from the coolant passing through it. The fins on the core absorb heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant.

During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.

Screw On Pressure Cap

The pressure cap is a cap that seals and pressurizes the cooling system. It contains a blow off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring of predetermined strength, which protects the radiator by relieving pressure if it exceeds 15 psi. The vacuum valve is held against its seat by a spring, which permits opening of the valve to relieve vacuum created in the cooling system as it cools off. The vacuum, if not relieved, might cause the radiator to collapse.

The pressure cap allows pressure in the cooling system to build up. As the pressure builds, the boiling point of the coolant goes up as well. Therefore, the coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat moves from the radiator to the cooler, passing air. The pressure in the cooling system can get too high; however, when the pressure exceeds the strength of the spring, it raises the pressure valve so that the excess pressure can escape. As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the cooling system. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator from collapsing.

Coolant Surge Tank

The coolant surge tank is connected to the engine cooling system by a pressure hose from the heater connection at the coolant pump and a vapor hose from the left hand radiator side tank.

As the engine temperature rises, the coolant heats and expands. The fluid displaced by the expansion flows into the coolant surge tank. When the engine is turned OFF, the coolant contracts as it cools and the pressure in the surge tank returns to atmospheric, by the unsealing of the vacuum valve in the screw-on pressure cap, if necessary.

Coolant level should be maintained at the indicated point on the side of the surge tank, when the engine is cold, by sighting the level externally. A coolant level switch is installed in the surge tank to alert the operator if the coolant level gets too low.

Air Baffles and Seals

The cooling system uses deflectors and air baffles to increase system cooling. Deflectors are installed under the vehicle to redirect air flow beneath the vehicle to flow through the radiator and increase cooling. Air baffles are also used to direct air flow into the radiator and increase cooling.

Water Pump

The water pump is a centrifugal vane impeller type pump. The pump consists of a housing with coolant inlet and outlet passages and an impeller. The impeller is a flat plate mounted on the pump shaft with a series of flat or curved blades or vanes. When the impeller rotates, the coolant between the vanes is thrown outward by centrifugal force. The impeller shaft is supported by one or more sealed bearings. These sealed bearings never need to be lubricated. With a sealed bearing, grease cannot leak out, and dirt and water cannot get in.

The purpose of the water pump is to circulate coolant throughout the cooling system. The water pump is driven by the crankshaft via the drive belt.

Thermostat

The thermostat is a coolant flow control component. It's purpose is to regulate the operating temperature of the engine. It utilizes a temperature sensitive wax-pellet element. The element connects to a valve through a piston. When the element is heated, it expands and exerts pressure against a rubber diaphragm. This pressure forces the valve to open. As the element is cooled, it contracts. This contraction allows a spring to push the valve closed.

When the coolant temperature is below 86°C (186°F), the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 86°C (186°F), the thermostat valve will open. The coolant is then allowed to circulate through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a restriction in the cooling system, even after it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.

Transmission Oil Cooler

The transmission oil cooler is a heat exchanger. It is located inside the left side end tank of the radiator. The transmission fluid temperature is regulated by the temperature of the engine coolant that surrounds the oil cooler as the transmission fluid passes down through the cooler.

The transmission oil pump pumps the fluid through the transmission oil cooler feed line to the oil cooler. The fluid then flows down through the cooler while the engine coolant absorbs heat from the fluid. The fluid is then pumped through the transmission oil cooler return line to the transmission.

The cooling system includes 2 dual speed engine cooling fan motors, both of which drive fans with 5 asymmetrical blades to reduce air noise. The fans remove heat from both the engine coolant flowing through the radiator and the refrigerant flowing through the air conditioning condenser. The fan and motor assemblies are mounted on a common shroud, which in turn is mounted onto the engine side of the radiator. The A/C condenser is mounted to the front of the radiator.

The fan motors are 12-volt, dual speed types. The internal construction of the fan motor consists of 4 brushes and 4 permanent magnets. A 3-wire pigtail harness is permanently attached to both motors and is attached to the polypropylene fan shroud at 2 locations by integral clips moulded as part of the shroud. Both motor harnesses are connected directly to the engine harness through a 3-pin sealed connector. This enables individual removal of the left and right fan and motor assemblies when necessary. The 2 electrical connectors are attached to the shroud by way of slide lock clips. Each motor is attached to the polypropylene fan shroud by 3 bolts installed at the threaded mounting flanges, which protrude symmetrically from the rear of the fan motor housing. The enclosed fan motor housing is constructed of yellow zinc coated steel. A drain hole is located in the bottom of the housing to allow for breathing and draining of any moisture ingress. Both fan motors rotate in an anti-clockwise direction when viewed from the fan motor side. Both fan and motor assemblies are balanced as a unit. Fan blades must not be separated from their respective motors. Fan motors and blades are serviced only as an assembled unit. The central nut attaching the fan blade to the motor shaft has a left-hand thread.

Each fan motor harness has one positive and 2 negative wires. To reduce the heat burden on the electrical connectors, the current draw is directed through separate negative terminals at the connector for each fan motor. The positive wire permanently connects battery voltage to the 2 positive brushes of each fan motor. The negative wires are each connected to one negative brush. When one negative wire per fan motor is grounded via the engine cooling fan relay 1, both cooling fan motors will operate at low speed. When both negative wires of each fan motor are grounded via the engine cooling fan relay 2, both cooling fan motors will operate at high speed.

Suppression capacitors located at the fan motor brush holders are incorporated. These suppression capacitors help eliminate fan motor noise through the radio speakers. If these capacitors are open, noise will be present through the radio speakers. If either of these capacitors were shorted to ground, the fan motors could run continuously or the fuses could fail. These capacitors are not serviced separately, the motor assembly must be replaced should a problem occur with either capacitor.

There are 2 relays used to control fan operation. The engine cooling fan relay 1 for low speed operation and the engine cooling fan relay 2 for high speed operation. The engine cooling fan relay 1 is energized by the body control module (BCM) in response to a request from the powertrain control module (PCM). The engine cooling fan relay 2 is energized by the PCM. After the PCM requests a change in the state of engine cooing fan relay 1, the BCM will send a serial data response message back to the PCM confirming it received the message. Serial data communication between the PCM and BCM is via the powertrain interface module (PIM). The PCM determines when to enable and disable both engine cooling fan relays based on inputs from the A/C request signal, the engine coolant temperature (ECT) sensor and the vehicle speed sensor (VSS).

Stage One - Both Fans Operate at Low Speed

The engine cooling fan relay 1 is energized by the BCM in response to a request from the PCM. When the PCM determines that the engine cooling fan relay 1 should be enabled, the PCM will send a message on the Class 2 serial data circuit to the PIM. The PIM will then convert the PCM Class 2 message to a UART message and supply this universal asynchronous receiver transmitter (UART) message to the BCM, via a serial data Normal Mode Message. This message will request the BCM to supply the needed ground signal for the engine cooling fan relay 1 to operate.

After the BCM provides the ground signal for the engine cooling fan relay 1, the BCM will send a message back to the PIM confirming that the ground signal was commanded. A failure in this BCM response communication, will cause a PIM DTC to set.

The engine cooling fan relay 1 will be turned ON and both fans driven at low speed when the A/C request indicates YES and either:

The low speed cooling fan operation is disabled when the engine cooling fan relay 1 is de-energized by the BCM via a request from the PCM. The PCM will request low speed fan disable via serial data communication to the BCM via the PIM. After the PCM requests a change in the state of engine cooling fan relay 1, the BCM will send a serial data response message back to the PCM confirming it received the message.

The engine cooling fan relay 1 will be turned OFF when any of the following conditions have been met:

Stage Two - Both Fans Operate at High Speed

The engine cooling fan relay 2 is controlled by the PCM. The PCM will only turn ON the engine cooling fan high speed relay fan if the engine cooling fan relay 1 has been ON for 2 seconds and the following conditions are satisfied:

The engine cooling fan relay 2 will be turned OFF when any of the following conditions have been met:

If the engine cooling fan relay 1 was OFF when the criteria was met to activate engine cooling fan relay 2, stage 2 fan operation will occur 1-5 seconds after the engine cooling fan relay 1 is turned ON.

If both engine cooling fan relays are ON, the PCM will turn OFF engine cooling fan relay 2 when any of the following conditions have been met:

The Stage 2 cooling fan operation has a minimum run-on time function of 30 seconds. Both cooling fans will be turned OFF if the vehicle speed is greater than 104 km/h (65 mph). Dependent upon input signals, ambient temperature, etc., the vehicle speed when all cooling fans will be turned OFF, is variable.