The engine cooling system consists of the following components:

Low Speed Operation for the Cooling Fan and Auxiliary Cooling Fans 1 and 2

When the engine temperature reaches 100°C (212°F), stage 1 of the primary cooling fan temperature switch closes and completes the ground circuit to the K26 fan control relay. The K26 relay is then activated and sends voltage through auxiliary coolant fan #1, through K52 fan control relay, through auxiliary coolant fan #2 to ground. Fan #1 and fan #2 are connected in series. Fan #1 is supplied a voltage and fan #2 is supplied a ground. This causes low speed operation of the auxiliary fans. The K26 relay also controls cooling fan low speed operation. K26 supplies voltage through the engine coolant fan resistor, through the cooling fan to ground. The engine cooling fan resistor limits the voltage supplied to the cooling fan which causes the cooling fan to operate in low speed. When the coolant temperature drops below 95°C (203°F) the cooling fan and Auxiliary coolant fans #1 and #2 will turn OFF. When A/C is requested low speed auxiliary fans #1 and #2 will not turn OFF.

High Speed Operation for the Cooling Fan and Auxiliary Cooling Fans 1 and 2

High speed fans are separated by two coolant temperatures. At 105°C (221°F) both auxiliary cooling fans will be activated for high speed. At 110°C (230°F) the cooling fan will be activated for high speed operation. At 105°C (221°F) the secondary cooling fan temperature switch closes and completes the ground circuit to the K28 and K52 fan control relays. This switches the auxiliary coolant fan #1 and auxiliary coolant fan #2 from a series low speed circuit to high speed independent fans. When K28 relay is energized fan #2 will receive an independent voltage supply. When K52 relay is energized fan #1 will receive an independent ground. At 110°C (230°F) stage 2 of the primary cooling fan temperature switch closes which completes the ground to energize the K67 fan control relay. This switches the cooling fan low speed operation through the coolant fan resistor to high speed operation by supplying direct voltage from K67 relay to the cooling fan. When the coolant temperature drops below 100°C (212°F) the auxiliary coolant fan #1 and fan #2 will switch back to low speed operation. When A/C is requested and refrigerant pressure is above 275 psi the auxiliary coolant fan #1 and fan #2 will not switch to low speed operation until pressure drops below 217 psi.

A/C Operation for the Cooling Fan and Auxiliary Cooling Fans 1 and 2 High and Low Speed

The A/C system has no effect on the cooling fan. The A/C system will only effect auxiliary coolant fan #1 and fan #2. When A/C is requested the ECM supplies ground to the K60 A/C compressor relay. The K60 relay is then activated sending voltage to the K87 fan control relay. The K87 relay is then activated and sends voltage to the auxiliary coolant fan #1. When the A/C pressure is below 275 psi voltage goes through the auxiliary coolant fan #1, through K52 fan control relay, through auxiliary coolant fan #2 to ground. Fan #1 and fan #2 are connected in series. Fan #1 is supplied a voltage and fan #2 is supplied a ground. This courses low speed operation of the auxiliary fans. When the A/C pressure is above 275 psi the A/C pressure switch closes and completes the ground circuit to the K28 and K52 fan control relays. This switches the auxiliary coolant fan #1 and auxiliary coolant fan #2 from a series low speed circuit to high speed independent fans. When K28 relay is energized fan #2 will receive an independent voltage supply. When K52 relay is energized fan #1 will receive an independent ground which allows both fans to operate at high speed. When A/C pressure is drops below 217 psi the auxiliary coolant fan #1 and fan #2 will switch back to low speed operation. When temperature is above 105°C (221°F) high speed auxiliary coolant fan #1 and fan #2 will not switch to low speed operation until temperature drops below 100°C (212°F).

Auxiliary Water Pump Operation

This pump only operates when the ignition is in the OFF position. When the engine temperature reaches 100°C (212°F), stage 1 of the primary cooling fan temperature switch closes and completes the ground circuit to the K26 fan control relay. The K26 fan control relay is then activated and sends voltage to the K22 auxiliary water pump relay. When the ignition is OFF voltage passes through the K22 relay to the auxiliary water pump to ground. When coolant temperature drops below 95°C (203°F) the cooling fan, auxiliary coolant fan #1, fan #2 and the auxiliary water pump will switch from low speed to OFF.

Coolant Temperature

The IPC illuminates the coolant temperature indicator when the following occurs:

Low Coolant Level

The IPC illuminates the low coolant indicator when the following occurs:

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 auxiliary water pump is mounted on the LH side of the radiator, which circulates coolant from the engine to the radiator. This pump only runs when the key is in the OFF position, along with the electric cooling fans at low speed. The pump becomes activated when coolant temperature reaches 100°C (212°F) and shuts off at 95°C (203°F). A failure causing this pump to operate when the vehicle is running will cause the engine to over heat.

Heater Auxiliary Water Pump

With the ignition ON, the heater auxiliary water pump runs continuously and increases the flow of coolant to the heater core. At low RPM or idle, coolant circulation to the heater core is low and A failure in this pump would result in poor passenger compartment heating. The pump is mounted on the RH strut tower,

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 crossflow 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:

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.