The engine cooling fan system consists of two electrical cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and the fan relays receive battery positive voltage from the underhood fuse block. The ground path is provided at G104.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the cooling fan s/p relay and the left cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time the cooling fan 2 relay coil is energized, closes the relay contacts, and provides battery positive voltage on the cooling fan motor supply voltage circuit to the left cooling fan. During high speed fan operation, both cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.

The PCM commands the low-speed fans ON under the following conditions:

The cooling fans will switch from low to OFF when the coolant temperature drops below 102°C (216°F).

The PCM commands the high-speed fans ON under the following conditions:

The cooling fans will switch from high to low, except when DTCs are set, when the coolant temperature drops below 106°C (223°F).

Engine Coolant

The IPC illuminates the engine coolant indicator and sends a class 2 message in order to activate an audible warning when the following occurs:

The IPC turns OFF the engine coolant indicator when the engine coolant falls below 125°C (257°F).

CHECK COOLANT LEVEL - 2

The IPC illuminates the CHECK COOLANT LEVEL - 2 indicator in the DIC when the IPC detects that the engine coolant level is below the normal operating range (signal circuit is high). The IPC receives a discrete input from the engine coolant level switch.

ENGINE COOLANT HOT/IDLE ENGINE - 44

The IPC illuminates the ENGINE COOLANT HOT/IDLE ENGINE - 44 indicator in the DIC and sends a class 2 message in order to activate an audible warning when the IPC determines that the coolant temperature is greater than 128°C (262°F). The IPC receives a class 2 message from the PCM indicating the coolant temperature.

The IPC turns OFF the indicator when the engine coolant falls below 125°C (257°F).

ENGINE HOT - AC OFF - 16

The IPC illuminates the ENGINE HOT - AC OFF - 16 indicator in the DIC when the dash integration module (DIM) detects that the engine temperature is above the normal operating range and has turned off the air conditioning in order to allow the engine to cool down. The IPC receives a class 2 message from the DIM requesting illumination.

ENGINE OVERHEATED/STOP ENGINE - 42

The IPC illuminates the ENGINE OVERHEATED/STOP ENGINE - 42 indicator in the DIC and sends a class 2 message in order to activate an audible warning when the powertrain control module (PCM) detects that the engine temperature is above the normal operating range. The IPC receives a class 2 message from the PCM requesting illumination.

The engine cooling system contains an engine coolant level switch which alerts the driver in the event of a coolant loss. When the engine coolant level switch reads a low coolant level in the surge tank, the switch opens. This sends a coolant loss signal to the IPC by the coolant level switch signal circuit. Ground is provided by G201 for the coolant level control.

The optional engine coolant heater (RPO K05) consists of two electrical heating elements fastened to the left and right sides of the engine block. These heating blocks are precisely machined to fit the engine block area. Each heating element is rated at 300 watts and supplies 1024 btu/hr. The engine coolant heater operates using 110-volt AC external power and warms the coolant in the engine block area for improved starting in very cold weather -29°C (-20°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The units are equipped with a detachable AC power cord. A weather shield on the cord protects the plug when not in use.

The cooling system maintains an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system removes 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 to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine is warmed, or the coolant will flow through the thermostat 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 heats and defrosts the passenger compartment.

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 the coolant 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 the coolant absorbs additional heat.

From the cylinder heads, the coolant is then forced into the radiator where the coolant 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. The radiator consists of a core and two 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 in order 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 also has a drain cock which is located in the bottom of the left tank. The drain cock includes the drain cock and drain cock seal.

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, the air absorbs heat and cools the coolant.

Surge Tank

The surge tank is a plastic tank with a pressure cap mounted to it. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system. The air space allows the coolant to expand and contract. The surge tank also provides a coolant fill point and a central air bleed location.

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.

Pressure Cap

The pressure cap seals and pressurizes the cooling system. The cap contains a blow-off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against the seat by a spring of predetermined strength, which protects the radiator by relieving pressure in excess of 18 psi. The vacuum valve is held against the seat by a spring, which permits opening of the valve in order to relieve vacuum created as the cooling system cools off. If not relieved, the vacuum 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, the faster the heat moves from the radiator to the cooler surrounding air. The pressure in the cooling system can get too high, however. When the pressure exceeds the strength of the spring, the pressure 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.

Air Baffles and Seals

The cooling system uses deflectors, air baffles, and air seals in order to increase system cooling. Deflectors are installed under the vehicle in order to redirect airflow beneath the vehicle and through the radiator, and to increase cooling. Air baffles also direct airflow into the radiator and increase cooling. Air seals prevent air from bypassing the radiator and A/C condenser. Air seals also prevent recirculation of the air for better hot weather cooling and A/C condenser performance.

Water Pump

The water pump is a centrifugal vane impeller type pump. The pump consists of a retaining plate, pulley 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 camshaft via the drive belt.

Thermostat

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

When the coolant temperature is below 85°C (185°F), the thermostat valve remains closed. This prevents circulation of the coolant from the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 85°C (185°F), the thermostat valve will open. The coolant is then allowed to circulate through the thermostat to the engine and then to the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a restriction in the cooling system, even after the valve has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.

Engine Oil Cooler

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

The engine oil pump draws the oil through the engine oil feed line to the oil cooler. The oil then flows down through the cooler while the engine coolant absorbs heat from the oil. The oil is then pumped through the oil return line to the oil filter, then to the main engine oil passage.

Transmission Oil Cooler

The transmission oil cooler is a heat exchanger. The cooler 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 through the cooler.

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