Intermittent
Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to INTERMITTENT OR POOR CONNECTIONS .
Looseness
If the fan assembly is loose, inspect the fan assembly for wear. Replace the fan assembly as necessary.
Observe the tip of the fan blade for lateral movement. Lateral movement occurs under various temperature conditions. A lateral movement measuring 6.5 mm (1/4 in) is normal. This amount of movement is not cause for replacement of the assembly.
Engine Overheating
| CAUTION | Check for adequate clearance between the fan blades and the thermometer sensor before starting the engine, as damage could occur. |
Use the following procedure in order to diagnose the causes of engine overheating
- Ensure that the engine is cool. This will allow complete disengagement of the fan clutch. Important: Testing the fan clutch by rotating the fan in a repeated clockwise/counterclockwise motion causes the clutch to free-wheel. Free-wheeling is a normal result of rotating the fan in this manner. Conduct further tests in order to determine if it is necessary to replace the fan clutch.
- Spin the fan and clutch assembly by hand. If the fan and clutch assembly easily revolves more than 5 times with no drag, replace the fan clutch.
- If the fan clutch performs correctly but exhibits drag, position a thermometer between the fan blades and the radiator. Use any of the following methods in order to position the thermometer: Insert the thermometer sensor through one of the existing holes in the fan shroud. Place the thermometer between the radiator and the shroud. On models that do not have holes in the fan shroud, drill a 5 mm (3/16 in) hole in the fan shroud. Insert the thermometer in the hole.
- Cover the radiator in order to induce a high engine temperature.
- Start the engine.
- Turn on the air conditioning.
- Operate the engine at 2,000 RPM.
- Wait for 5 to 10 minutes while the temperature increases sufficiently to allow the fan clutch to engage. The following conditions indicate that the fan clutch has engaged: A roaring noise or an increase in fan noise occurs. The thermometer reading drops approximately 3-10°C (5-15°F). Important: Do not continue the test past a thermometer reading of 88°C (190°F). Continuing the test past a thermometer reading of 88°C (190°F) may cause engine overheating.
- Observe the thermometer reading when the fan clutch engages. The following conditions are cause for replacement of the fan clutch: The fan clutch does not engage while the temperature measures 65-90°C (150-195°F). If the fan clutch does not engage while the temperature is within this range, verify that the fan clutch was disengaged at the beginning of the test. Both of the following conditions exist: No temperature drop occurs The fan noise level is constant from the beginning of the test until the time when the engine temperature reaches 88°C (190°F). Do not continue the test past a thermometer reading of 88°C (190°F) in order to prevent overheating.
- Perform the following steps as soon as the fan clutch engages: Remove the radiator cover. Turn OFF the air conditioning. Operate the engine at approximately 1,500 RPM until the coolant returns to the normal operating temperature.
- Observe the operation of the fan clutch. The fan clutch should disengage after several minutes. Disengagement of the fan clutch is indicated by a decrease in fan noise or roar. If the fan clutch does not disengage after several minutes, the fan clutch should be replaced.
Radiator Cleaning
An engine will overheat if the radiator has any of the following conditions
- Leaks
- Dirt or obstructions in the core
Use a soft bristle brush and clean hot water or a mild detergent solution in order to clean the outside of the radiator core. A car wash or dishwashing liquid is a suitable detergent.
A common city water hose may also be used in order to clean the outside of the radiator. Remove the nozzle from the hose prior to use in order to prevent damage to the fins.
Use one of the following solutions in order to pressure flush and clean the inside of the core tubes
- Clean hot water
- Mild car wash
- Dishwashing liquid
Use the following steps in order to test the radiator for restrictions
- Warm the engine.
- Turn off the engine.
- Feel the radiator. The radiator should be hot along the left side and warm along the right side. There should be an even temperature rise from right to left. Cold spots in the radiator indicate clogged sections. Refer to «Cooling System Description and Operation»(ref-173517-S32814970752005031700000) for a radiator diagram.
Coolant Heater
The optional engine coolant heater (RPO KO5) is designed to warm the coolant in the engine block area for improved starting in very cold weather (temperatures below -29°C (-20°F)). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The engine coolant heater operates using AC external power and a heating element installed in the water jacket of the engine block. The heating element warms the coolant when the heater cord is plugged into an AC power source.
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.
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.
Some engine applications, coolant is also directed to the throttle body. There it circulates through passages in the casting. The coolant assists in regulating the throttle body temperature.
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 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.
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.
During vehicle use, the coolant is heated 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.
Coolant Recovery System
The coolant recovery system consists of a plastic coolant recovery reservoir, an overflow tube, and a pressure cap on the radiator. The recovery reservoir is also called a recovery tank or expansion tank. It is partially filled with coolant and is connected to the radiator fill neck with the overflow tube. Coolant can flow back and forth between the radiator and the reservoir.
In effect, a cooling system with a coolant recovery reservoir is a closed system. When the pressure in the cooling system gets too high, it will open the pressure valve in the pressure cap. This allows the coolant, which has expanded due to being heated, to flow through the overflow tube and into the recovery reservoir. As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum opens the vacuum valve in the pressure cap, allowing some of the coolant in the reservoir to be siphoned back into the radiator. Under normal operating conditions, no coolant is lost. Although the coolant level in the recovery reservoir goes up and down, the radiator and cooling system are kept full. An advantage to using a coolant recovery reservoir is that it eliminates almost all air bubbles from the cooling system. 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 relief 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.
Cooling Fan and Clutch
The engine cooling fan and clutch are driven by the crankshaft via the drive belt. The cooling fan draws air through the radiator to improve the transfer of heat from the coolant to the atmosphere. As the fan blades spin, they pull cool, outside air past the radiator core. The fan clutch drives the cooling fan. The fan clutch controls the amount of torque that is transmitted from the crankshaft to the fan blades. The clutch allows more torque to engage on the fan when the engine operating temperature increases and/or the vehicle speed is low. As the torque increases, the fan turns more quickly. The fan clutch decreases the torque applied to the cooling fan when the engine temperature decreases and/or the vehicle speed is high. As the torque decreases, the fan speed decreases.
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.
Water Pump
The water pump is a centrifugal vane impeller type pump. The pump consists of a housing with coolant inlet and outlet passages, a retaining plate, pulley 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.
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 a 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 85°C (185°F) for diesel engines and below 91°C (195°F) for gas engines, the thermostat valve remains closed. This prevents circulation of the coolant from the radiator and allows the engine to warm up. After the coolant temperature reaches 85°C (185°F) or 91°C (195°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, 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.
Engine Oil Cooler
The engine oil cooler is a heat exchanger. It is located inside the left side end tank of the radiator. The engine oil temperature is controlled by the temperature of the engine coolant that surrounds the oil cooler in the radiator.
The engine oil pump pumps the oil through the engine oil cooler line to the oil cooler. The oil then flows through the cooler where the engine coolant absorbs heat from the oil. The oil is then pumped through the oil cooler return line, to the oil filter, to the engine block oil system.
Transmission Oil Cooler
The transmission oil cooler is a heat exchanger. It is located inside the right side end tank of the radiator. The transmission fluid temperature is regulated by the temperature of the engine coolant in the radiator.
The transmission oil pump, pumps the fluid through the transmission oil cooler line to the transmission oil cooler. The fluid then flows 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.
