Cooling System: Description and Operation

Cooling System Description and Operation

Coolant Fan Circuit Operation
The engine cooling system consists of the following components:
- Electric cooling fan
- Auxiliary engine coolant fan #1
- Auxiliary engine coolant fan #2
- Primary cooling fan temperature switch
- Secondary cooling fan temperature switch
- A/C compressor refrigerant pressure switch
- Heater water auxiliary pump
- Auxiliary water pump
- Engine coolant fan resistor
- Six fan control relays

Auxiliary Fans Low Speed, Electric Cooling Fan Low Speed
B+ is supplied to the heater water auxiliary pump whenever the ignition switch is in the ON position. When the engine temperature reaches 100° C (212° F), the primary cooling fan temperature switch stage 1 will close, enabling the fan control relay K26 to energize. When the fan control relay K26 energizes, B+ from fuse #52 is applied to the auxiliary coolant fan #1 (auxiliary engine coolant fan #1 is wired in series with auxiliary engine fan #2, through the normally closed contacts of the fan control relay K52). This will cause the auxiliary coolant fans #1 and #2 to operate at low speed. The fan control relay K26 will also supply B+ to the engine coolant fan resistor, voltage passes through the resistor to the electric coolant fan. The engine coolant fan resistor will cause the engine coolant fan to operate at low speed. The primary cooling fan temperature switch stage 1 contacts will open when the coolant temperature reaches 95° C (203° F). This will turn all 3 fans OFF, unless the air conditioning system is ON.

Auxiliary Fans High Speed
When the engine temperature reaches 105° C (221° F), the secondary cooling fan temperature switch contacts will close and energize the fan control relays K52 and K28. When the fan control relay K52 energizes, it will ground terminal B of auxiliary engine coolant fan #1. Terminal A of the auxiliary engine fan #1 still receives B+ from fan control relay K26.The auxiliary coolant fan #1 is no longer in series with the auxiliary engine coolant fan #2 and will now operate at full speed. When the fan control relay K28 is energized, B+ from fuse #40 will be applied to terminal A of the auxiliary engine coolant fan #2. The auxiliary coolant fan #2 is no longer in series with the auxiliary engine coolant fan #1 and operates at full speed. Terminal B of the auxiliary coolant fan #2 is permanently grounded to G 103. With the stage 1 contacts of the primary cooling fan temperature switch closed, the electric cooling fan will continue to operate. The secondary cooling fan temperature switch contacts will open when the coolant temperature reaches 100° C (212° F). This will cause the auxiliary engine coolant fans #1 and #2 to operate at low speed.

Electric Coolant Fan High Speed
When the engine coolant temperature reaches 110°C (230° F), the primary cooling fan temperature switch stage 2 will close energizing the fan control relay K67. When the fan control relay K67 energizes, B+ from fuse #42 will be applied directly to terminal A of the engine coolant fan (bypassing the engine coolant fan resistor ) and the engine coolant fan will operate at full speed. All the other operations that were taking place before the coolant temperature reached 110° C (230° F) will remain in effect. The primary cooling fan temperature switch stage 2 contacts will open when the coolant temperature reaches 105° C (221° F) and the primary engine coolant fan will shut off.
At coolant temperatures above approximately 110° C (230° F), all three coolant fans are operating at full speed. Only five of the six relays operate at this time, unless the air conditioning system is turned ON. In this case, the fan control relay K87 and the A/C compressor relay K60 will also operate.

Engine Cooling Fans (A/C Operation)
When the A/C compressor is turned on, fan control relay K87 is energized and the auxiliary engine coolant fans #1 and #2 will operate in low speed. In order to prevent inadmissible high refrigerant pressure in the refrigerant circuit, the auxiliary engine coolant fans #1 and #2 are switched from the low speed to the high speed at refrigerant pressures above approximately 1 900 kPa (275 psi). When the pressure drops below approximately 1500 kPa (217 psi), the auxiliary engine coolant fans #1 and #2 are switched back to the low speed.

Water Auxiliary Pump
When the ignition is in the OFF position and the engine coolant temperature reaches 100° C (212° F), the primary cooling fan temperature switch stage 1 will close, enabling the fan control relay K26 to energize. When the fan control relay K26 energizes, B+ from fuse #52 is applied through the normally closed auxiliary water pump relay K22, allowing the water auxiliary pump to operate. The fan control relay K26 will also supply B+ to the engine coolant resistor, allowing voltage to pass through the resistor to the electric cooling fan. The engine cooling fan resistor will cause the engine cooling fan to operate at low speed. When the engine coolant temperature reaches 95° C (203° F), the primary cooling fan temperature switch stage 1 will open, de-energizing fan control relay K26. This will turn the water auxiliary pump and engine cooling fan OFF.

Engine Coolant Indicator(s)
Coolant Temperature
The IPC illuminates the coolant temperature indicator when the following occurs:
- The IPC determines that the coolant temperature is greater than 121° C (248° F) from the engine coolant temperature gage sensor.
- The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

Low Coolant Level
The IPC illuminates the low coolant indicator when the following occurs:
- The IPC detects a low coolant level condition (signal is low) from the coolant level sensor.
- The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

Cooling System
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 coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly.

Cooling Cycle
Coolant flows from the radiator outlet and into the water pump inlet. Some coolant flows from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost capability as the coolant warms up.
Coolant also flows from 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 then flows 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.
From the cylinder heads, the coolant flows to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine reaches normal operating temperature, or it will flow through the thermostat and into the radiator where it is cooled. At this point, the coolant flow cycle is completed.
Efficient 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 suitable drinking water. The coolant solution carries excess heat away from the engine to the radiator, where the heat is dissipated to the atmosphere.

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 mounted on the pump shaft and consists of a series of flat or curved blades or vanes on a flat plate. 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. The sealed bearings never need to be lubricated. Grease cannot leak out, dirt and water cannot get in as long as the seal is not damaged or worn.
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.

Auxiliary Water Pump
The electrical auxiliary water pump is mounted on the LH side of the radiator, which provides the additional flow of coolant across the radiator. This pump only runs when the key is in the OFF position, along with the electric cooling fan at low speed. The pump becomes activated when coolant temperature reaches 100° C (212° F) and shuts off at 95° C (203° F).

Heater Water Pump
The continuously running electric heater water pump, mounted on the RH strut tower, increases the flow of coolant to the heater core. At low RPM or idle, coolant circulation to the heater core is low and can result in poor passenger compartment heating performance. A failure in this pump would result in poor passenger compartment heating.

Thermostat
The thermostat is a coolant flow control component. It's purpose is to help regulate the operating temperature of the engine. It utilizes a temperature sensitive wax-pellet element. The element connects to a valve through a small piston. When the element is heated, it expands and exerts pressure against the small piston. 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 the rated thermostat opening temperature, the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up. After the coolant temperature reaches the rated thermostat opening temperature, 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, 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.

Radiator
The radiator is a heat exchanger. It consists of a core and two tanks. The aluminum core is a tube and fin Cross flow design that extends from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer to the atmosphere.
The inlet and outlet tanks are a molded, high temperature, nylon reinforced plastic material. A high temperature rubber gasket seals the tank flange edge to the aluminum core. 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 located in the bottom of the left hand tank. The drain cock unit includes the drain cock and drain cock seal.
The radiator removes heat from the coolant passing through it. The fins on the core transfer heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant.

Surge Tank
The surge tank is a plastic tank with a threaded pressure cap. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system that allows the coolant to expand and contract. The surge tank provides a coolant fill point and a central air bleed location.
During vehicle use, the coolant heats and expands. The increased coolant volume flows into the surge tank. As the coolant circulates, any air is allowed to bubble out. Coolant without air bubbles absorbs heat much better than coolant with bubbles.

Pressure Cap
The pressure cap seals 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, which protects the radiator from excessive cooling system pressure. 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 and/or coolant hoses to collapse.
The pressure cap allows cooling system pressure to build up as the temperature increases. As the pressure builds, the boiling point of the coolant increases. Engine 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 transfers from the radiator to the cooler, passing air.
The pressure in the cooling system can get too high. When the cooling system pressure exceeds the rating of the pressure cap, it raises the pressure valve, venting the excess pressure.
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 surge tank. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator and coolant hoses from collapsing.

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

Engine Oil Heat Exchanger
The engine oil heat exchanger is mounted to the top of the engine block, under the intake manifold flange. Oil is pumped to the oil filter, to the heat exchanger, and then to the oil passages in the engine for lubrication. The exchanger provides the following two functions:
- Engine coolant warms up faster than the engine oil. During cold operation, the coolant warms the oil and provides better flow during cold engine operation.
- After the engine reaches normal operating temperature, the engine oil temperature will exceed the engine coolant temperature. The coolant flowing through the engine oil cooler will absorb heat from the engine oil. Cooling the engine oil extends oil life and helps reduce internal engine wear.

Coolant Heater
The optional engine coolant heater (RPO K05) operates using 110-volt AC external power and is designed to warm 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 unit is equipped with a detachable AC power cord. A weather shield on the cord is provided to protect the Plug when not in use.