Cooling System Fundamentals

Transcription

1 Cooling System Fundamentals After studying this chapter, you will be able to: Summarize the functions of a cooling system. Explain the operation and construction of major cooling system components. Compare cooling system design variations. Explain the importance of antifreeze. Discuss safety procedures to follow when working with cooling systems. Correctly answer ASE certification test questions on cooling system construction and operation. This chapter explains the design, construction, and operation of cooling systems. You must fully understand how different cooling systems work before learning to service and repair them. A cooling system must control the operating temperature of the engine. During startup, it must help the engine warm to operating temperature quickly to lower emissions. After the engine has warmed up, the cooling system must maintain a constant engine operating temperature for maximum efficiency. Without a properly operating cooling system, an engine can "self-destruct" in a matter of minutes. lntemal engine parts can overheat and partially melt, causing the engine to "lock up," or seize (reciprocating assembly no longer moves freely). For this and other reasons, it is important that you fully understand the information in this chapter Cooling System Functions A cooling system has several functions. It must remove excess heat from the engine, maintain a constant engine operating temperature, increase the temperature of a cold engine quickly, and provide a means for warming the passenger compartment. Removing Engine Heat The burning air-fuel mixture produces a tremendous amount of heat. Combustion flame temperatures can reach 4500 F (2500 C). This is enough heat to melt metal parts. Some combustion heat is used to produce expansion and pressure for piston movement. Most combustion heat flows out with the exhaust gas or flows into the metal parts of the engine. Without removal of this excess heat, the engine would be seriollsly damaged in a matter of minutes. Maintaining Operating Temperature Engine operating temperature is the temperature the engine coolant (water and antifreeze mixture) reaches under normal running conditions. Typically, an engine's operating temperature is between 180 F and 210 F (80 C and loodc). When an engine warms to operating temperature, its parts expand. This ensures that all part clearances are correct. It also ensures proper combustion, emission output levels, and engine performance. Reaching Operating Temperature Quickly An engine must warm up rapidly to prevent poor combustion, part wear, oil contamination, reduced fuel economy, increased emissions, and other problems. A cold engine suffers from several problems. For instance, the aluminum pistons in a cold engine will not be expanded by heat. This can cause too much clearance between the pistons and the cylinder walls. The oil in a cold engine will also be very thick. This can reduce lubrication and increase engine wear. The air-tuel mixture will not vaporize and burn as efficiently in a cold engme. 725

2 726 Section 6 Cooling al1d Lubrication Systems Heater Operation A cooling system commonly circulates coolant to the vehicle's heater. Since the engine coolant is warm, its heat can be used to warm the passenger compartment. See Figure Note! Refer to Chapter 75, Heating and Air Conditioning Fundamentals, and Chapter 76, Heating and Air Conditioning Service, for more infolmation on heaters. Cooling System Operation When the engine is running, the water pump forces coolant to circulate through the engine water jackets (internal passages in the engine). A drive belt often powers the water pump. The water pump can also be gear-driven off the crankshaft. While the engine is cold, the thermostat remains closed, so coolant circulates inside the engine. This helps warm the engine quickly. Thermostat Inlet Te mpe ratu re -It:""""-=--tt-<tt-:f sensor Fan relay Filler cap Radiator overflow tube Water pump reservoir tank Radiator fan Radiator radiator hose Figure Study the basic names and locations for parts of a cooling system. This will help you as each part is explained in detail. (Mazda)

3 Chapter 39 Cooling System Fundamentals 727 When the engine reaches operating temperature, the thermostat opens. Heated coolant then flows through the radiator. Excess heat is transferred from the coolant to the air flowing through the radiator. Heat in Cooling System Types There are two major types of automotive cooling systems: air cooling systems and liquid cooling systems. Air Cooling Systems An air cooling system uses large cylinder cooling fins and outside air to remove excess heat from the engine. The cooling fins increase the surface area of the metal around the cylinder. This allows enough heat to transfer from the cylinder to the outside air. Look at Figure An air cooling system commonly uses plastic or sheet metal ducts and shrouds (enclosures) to route air over the cylinder fins. Thermostatically controlled flaps regulate airflow and engine operating temperature. Tech Tip! Air-cooled automotive engines are rare. Most late-model vehicles have liquid-cooled engines. Liquid Cooling Systems A liquid cooling system circulates coolant (a solution of water and antifreeze) through the water jackets. The coolant then collects excess heat and carries it out of the engine. Figure 39-2 compares liquid and air cooling. Figure 39-3 shows how combustion heat is transferred into the coolant. Heat enters engine parts engine part Coolant Figure Combustion heat transfers into the cylinder wall and then into the coolant. Coolant carries heat away from the engine. A liquid cooling system has several advantages over an air cooling system, including: More precise control of engine operating temperature. Less temperature variation inside engine. Reduced exhaust emissions because of better temperature control. Improved heater operation to warm passengers. Conventional and Reverse Flow Cooling With conventional coolant flow, hot coolant flows from the cylinder head to the radiator. After being cooled in the radiator, the coolant flows back into the engine block. This is the most common coolant flow direction. Reverse flow cooling follows the opposite course: cool coolant enters the head and hot coolant exits the block to return to the radiator. Reversing the flow of the coolant helps keep a more uniform temperature throughout the engine, especially around the hot exhaust valves. Reverse flow cooling can be found on highperformance engines. Basic Cooling System Figure An air-cooled engine has large fins on the cylinder to dissipate heat into surrounding air. A water-cooled engine has water jackets around each cylinder to collect heat. (Robert Bosch) The basic parts of a cooling system are shown in Figure Refer to this illustration as each part is introduced. Water pump-forces coolant through the engine and other system parts. Radiator hoses-connect the engine to the radiator. Radiator-Transfers engine coolant heat to outside air. Fan-Draws air through the radiator.

4 728 Section 6 Cooling and Lubrication Systems Thermostat-Controls coolant flow and engine operating temperature. Water Pump The water pump is an impeller or centrifugal pump that forces coolant through the engine block, cylinder head, intake manifold, hoses, and radiator. It is often driven by a belt nmning off the crankshaft pulley. In some cases, the pump is gear-dr iven directly off the crankshaft. Water pump impellers can be made of steel or plastic. The impeller blades can be curved or straight. Straight blades, like paddle wheels, are sometimes used to reduce engine power consumption. Look at Figure The major parts of a typical water pump include the: Water pump impeller-disk with fan-like blades, the impeller spins and produces pressure and flow, Figure Water pump shaft-steel shaft that transfers turning force from the hub to the impeller. Water pump seal-prevents coolant leakage between pump shaft and pump housing, Figure Water pump bearings-plain or ball bearings that allow the pump shaft to spin freely in housing. Water pump hub-provides mounting place for belt pulley and fan. Water pump housing-iron or aluminum casting that forms the main body of pump. The water pump normally mounts on the front of the engine. With some transverse (sideways-mounted) engines, it bolts to the side of the engine and extends toward the front. Fan hub Housing Impeller Inlet from radiator Outlet to water jacket Figure Cutaway of a simplified water pump. Note how the spinning impeller throws coolant outward to produce pressure and flow. (OaimlerChrysler) Vent hole Impeller seat Figure Side cutaway view of water pump shows how the seal keeps coolant from leaking out of the vent hole. (Chevrolet) Crank pulley Water pump pulley Ribbed belt Figure The fan belt turns the water pump pulley to operate the pump. This is a modern ribbed belt that powers all accessory units. (Ford) A water pump gasket fits between the engine and pump housing to prevent coolant leakage. RTV sealer or a rubber seal may be used instead of a gasket. Water Pump Operation Figure 39-7 illustrates water pump action and coolant flow through an engine. The spinning engine crankshaft pulley causes the drive belt to turn the water pump pulley, pump shaft, and impeller. The coolant trapped between the impeller blades is thrown outward by centrifugal force. This produces suction (vacuum) in

5 Chapter 39 Cooling System Fundamentals 729 hose, and into the pump. After being thrown outward and pressurized, the coolant flows into the engine. It circulates through the block, around the cylinders, up through the cylinder head(s), through the thermostat, and back into the radiator. Figure The water pump pulls coolant out of the bottom of the radiator and through the engine block, heads, and intake manifold. Hot coolant then reenters the radiator for cooling. (Ford) the central area of the pump housing. It also produces pressure in the outer area of the housing. Since the pump inlet opening is near the center, coolant is pulled out of the radiator, through the lower Electric Water Pump An electric water pump uses a large dc motor and an impeller to force coolant through the engine's water jackets. It replaces a belt-driven water pump. The electj.ic water pump assembly often bolts to the side of the engine and has one radiator hose connected to it. When the BCU senses that the engine has reached a predetermined operating temperature, it will energize the electric water pump to maintain the correct engine temperature. Since the electric water pump does not tum until needed, it allows the engine to reach operating temperature more quickly for improved efficiency. The speed of the electric water pump can also be controlled by the BCU to reduce energy consumption. Radiator and Heater Hoses Radiator hoses carry coolant between the engine water jackets and the radiator. Being flexible, hoses can withstand the vibrating and rocking of the engine on its motor mounts without breakage. Look at Figure Heater core Thermostat housing Water pump Upper radiator hose Reservoir hose Lower radiator Radiator Radiator cap hose Figure Radiator hoses carry coolant between the engine and the radiator. Heater hoses carry hot coolant to heater core in the passenger compartment, under the dash.

6 730 Section 6 Cooling and Lubrication Systems Molded radiator hose cannot be bent Wire-type clamp I~I Flexible radiator hose can be bent Figure Two basic types of radiator hoses. (OaimlerChrysler) The upper radiator hose normally connects to the thermostat housing on the intake manifold or cylinder head. Its other end fits on the radiator. The lower hose often connects the water pump inlet and the radiator. A molded hose is manufactured in a special shape, with bends to clear the cooling fan and other parts. It must be purchased to fit the exact year and make of car. See Figure A flexible hose has an accordion shape and can be bent to different angles. The pleated construction allows the hose to bend without collapsing and blocking flow. The flexible hose is also called a universal-type radiator hose. A hose spring is frequently used in the lower radiator hose to prevent the hose from collapsing. The lower hose is exposed to suction from the water pump. The spring ensures that the inner lining of the hose does not tear away, close up, and stop circulation. Caution! Never remove the spring from the inside of a radiator hose. If you do, the hose can collapse and cause engine overheating damage. Heater hoses are small-diameter hoses that carry coolant to the heater core (small radiator-like device under the dash). Refer to Figure Hose clamps hold the radiator hoses and heater hoses on their fittings. Three types of hose clamps are pictured in Figure A worm-drive hose clamp uses a worm gear that engages slots in the clamp strap to allow tightening around the hose. It is the most common type of replacement hose clamp. Radiator The radiator transfers coolant heat to the outside air. The radiator is normally mounted in the front of the engine. Cool outside air can then flow freely through it. See Figure Figure Three basic types of hose clamps. Worm drive clamp is the most common. Spring-type clamp requires hose clamp pliers with a groove cut in the jaws. (OaimlerChrysler) A radiator typically consists of five components: Radiator core-center section of the radiator. Made up of tubes and cooling fins. Radiator tanks-metal or plastic ends that fit over the core tube ends to provide storage for coolant and fittings for hoses. Radiator filler neck-opening for adding coolant. Also holds the radiator cap and overflow tube. Transmission oil cooler-inner tank for cooling automatic transmission or transaxle fluid. Radiator petcock-fitting on the bottom of the tank for draining coolant. Radiator Action Under normal operating conditions, hot engine coolant circulates through the radiator tanks and core. Heat transfers into the core's tubes and fins. Cooler air flows over and through the radiator fins, so heat is removed from the radiator. This reduces the temperature of the coolant before it flows back into the engine. Radiator Types The two types of radiators are the crossflow and the downflow. Both are shown in Figure The tanks on a downflow radiator are on the top and bottom of the core, and the core tubes run vertically between the tanks. Hot coolant from the engine enters the top tank. The coolant flows downward through the core tubes. After cooling, the coolant flows out of the bottom tank and back into the engine. A cross flow radiator is a more modem design that has its tanks on the sides of the core. The core tubes are arranged for horizontal coolant flow. The tank with the radiator cap is normally the outlet tank. A crossflow radiator can be shorter than a downflow radiator, allowing for a lower hood line. Look at Figure

7 Chapter 39 Cooling System Fundamentals 731 Inlet tank O-ring gasket O-ring gasket Outlet tank Radiator cap Filler neck - Nut Radiator core Transmission oil cooler Rubber gasket Washer Figure Exploded view of the major parts of a cooling system. (General Motors) Inlet from engine Inlet from engine Cooling fins Filler cap Filler cap Direction of coolant flow Direction of coolant flow Transmission oil cooler Core tubes Outlet to engine Cooling fins Outlet to engine Transmission A oil cooler B Core tubes Figure Two types of radiators. A-A downflow radiator has core tubes running up and down. 8-A crossflow radiator has cooling tubes running horizontally. The crossflow radiator is more common on late-model cars. (DaimlerChrysler) Transmission Oil Cooler A transmission oil cooler is often placed in the radi ator on cars with automatic transmissions or trans axles to prevent the transmission fluid from overheating. It is a Radiator tanks can be made of metal or plastic. With metal radiator tanks, the core and tanks are soldered together. With plastic radiator tanks, rubber seals fit between the tanks and core to prevent leakage.

8 732 Section 6 Cooling and Lubrication Systems small tank enclosed in one of the main radiator tanks. Since the transmission fluid is hotter than the engine coolant, heat is removed from the fluid as it passes through the radiator and cooler, Figure In downflow radiators, the transmission oil cooler is located in the lower tank. In crossflow radiators, the oil cooler is in the tank having the radiator cap. Line fittings from the cooler extend through the radiator tank to the outside. Metal lines from the automatic transmission or transax1e connect to these fittings. The transmission oil pump forces the fluid through the lines and cooler, Figure Figure shows how the radiator can be mounted next to the air-conditioning condenser. With other vehicles, Figure Note how this vehicle has a radiator and airconditioning condenser mounted side-by-side. Many vehicles have the condenser in front of the radiator. (Honda) however, the condenser is usually mounted in front of the radiator. With side-by-side mounting, cooler air flows through the radiator. Radiator core Transmission oil cooler gasket Washer Figure Transmission oil cooler prevents overheating of automatic transmission fluid. lit is a small tank inside one of the radiator tanks. Note transmission line fittings. (Buick) transmission Radiator Direction of flow Figure Automatic transmission lines run from the transmission to the transmission oil cooler fittings. (Cadillac) Radiator Cap The radiator cap performs several functions: Seals the top of the radiator filler neck to prevent leakage. Pressurizes the system to raise the boiling point of coolant. This keeps coolant from boiling and turning to steam. Relieves excess pressure to protect against system damage. In closed systems, it allows coolant flow between the radiator and the coolant reservoir. The radiator cap locks onto the radiator tank filler neck or on the reservoir tank. Rubber or metal seals make the cap-to-neck joint airtight. Radiator caps can be made of metal or plastic. Radiator Cap Pressure Valve The radiator cap pressure valve, Figure 39-16, consists of a spring-loaded disk that contacts the filler neck. The spring pushes the valve into the neck to form a seal. When water is placed under pressure, its boiling point increases. Normally, water boils at 212 F (loo C). However, for every pound of pressure increase, water's boiling point goes up about 3 F (-16 C). The radiator cap works on this principle. Typical radiator cap pressure is psi ( kpa). This raises the boiling point of the engine coolant to F ( C). Many surfaces inside the engine's water jackets can be above 212 F (loo C).

9 Chapter 39 Cooling System Fundamentals 733 Pressure relief valve spring Upper sealing gasket Lower sealing gasket Safety stop Figure A radiator pressure cap screws onto the radiator filler neck or reservoir tank. Rubber or metal seals prevent leakage. (OaimlerChrysler) If the engine overheats and pressure exceeds the cap rating, the pressure valve opens. Excess pressure and steam force the coolant out of the ovelilow tube and into the reservoir (or onto the ground in older systems). This prevents high pressure from rupturing the radiator, gaskets, seals, or hoses. Radiator Cap Vacuum Valve The radiator cap vacuum valve opens to allow flow back into the radi ator when the coolant temperature drops after engine operation. It is often a small valve located in the center of the bottom of the cap. Look at Figure The cooling and contraction of the coolant and air in the system decrease the coolant volume and pressure. Without a cap vacuum valve, the radiator hoses and radiator tanks could collapse from outside pressure. Closed and Open Cooling Systems A closed cooling system uses an expansion tank, or reservoir, and a radiator cap with pressure and vacuum valves. The overflow tube is routed into the bottom of the reservoir tank. Pressure and vacuum valve action pull coolant in and out of the reservoir tank as needed. This keeps the cooling system correctly filled at all times. Figure shows the operation of a closed cooling system. When the engine heats up, the coolant expands and opens the cap pressure valve. Instead of leaking onto the ground, the coolant flows into the reservoir. After the engine has been shut off, the coolant temperature drops and its volume decreases. This causes the vacuum valve to open. Atmospheric pressure (system suction) then forces coolant back into the radiator. This compensates for any small system leaks, keeping the system properly filled. A Coolant heats and expands Flow back into reservoir Overflow Gasket retainer ri-~~:rl Stainless steel swivel top Rubber seals B Coolant fills radiator Coolant pulled out of reservoir Coolant temperature and volume drops Radiator top tank ~ Vacuum valve Figure This cutaway view shows how the pressure cap installs and seals on the radiator filler neck. (OaimlerChrysler) Figure Study pressure cap operation. A-When the engine heats up, coolant expands. Excess fluid opens the cap pressure valve and coolant enters reservoir for reuse. 8-When the engine is shut off, coolant temperature drops. This causes coolant to reduce in volume. Cap vent valve opens to let coolant flow back into the radiator. (Ford)

10 734 Section 6 Cooling and Lubrication Systems Note! The reservoirs in some closed cooling systems are under full cooling system pressure. Pressurized reservoirs have a pressure cap rather than a vented cap. The radiators in systems with pressurized reservoirs generally do not have a traditional radiator cap. An open cooling system does not use a coolant reservoir. The overflow tube allows excess coolant to leak onto the ground. Also, it does not provide a means of adding fluid automatically. The open cooling system is no longer used on automobiles. It has been replaced by the closed system, which requires less maintenance. Cooling System Fans A cooling system fan pulls air through the core of the radiator and over the engine to help remove heat. It increases the volume of air flowing through the radiator, especially when the car is standing still. The fan is driven by a fan belt or an electric motor. Engine-Powered Fans An engine-powered fan bolts to the water pump hub and pulley. Sometimes, afan spacer fits between the fan and pulley to move the fan closer to the radiator. A flex fan has thin, flexible blades that alter ai rflow with engine speed. At low speeds, the fan blades remain curved and pull air through the radiator. At higher engine speeds, the blades flex until they are almost straight. This reduces fan action and saves engine power, Figure A fluid coupling fan clutch is designed to slip at higher engine speeds. It performs the same function as a flexible fan. The clutch is filled with silicone-based oil. At a specific fan speed, there is enough load to make the clutch slip, Figure A thermostatic fan clutch has a temperaturesensitive, bimetal spring that controls fan action. The spring controls oil flow in the fan clutch. When cold, the spring causes the clutch to slip, speeding engine warmup. After reaching operating temperature, it locks the clutch, providing forced-air circulation. See Figure Friction chamber Clutch plate Figure This is a fluid coupling fan clutch. A clutch plate operating in silicone-based oil causes enough friction at low speeds to turn fan. A high-speed load overcomes the friction, and the fan slips to save energy. (DaimlerChrysler) Plastic fan Thermostatic spring Water pump assembly Figure Note the construction of a flex-type radiator fan. High rpm causes fan blades to flex (bend), reducing blowing action. Note how a spacer is used to move fan closer to radiator. (Ford) Figure A thermostatic fan clutch is similar to a fluid coupling fan clutch. A bimetal spring is used to control clutching action. The fan only operates when the engine is hot and when the spring activates the clutch mechanism. (Toyota)

11 Chapter 39 Cooling System Fundamentals 735 Electric Cooling Fans An electric cooling fan uses an electric motor and a thermostatic switch (coolant temperature sensor) to provide cooling action. An electric fan is needed on frontwheel-drive cars having transverse-mounted engines. In these vehicles, the water pump is nonnally located away from the radiator. Nevertheless, electric engine fans can be used on any engine/transmission layout. Look at Figure Thefan motor is a small dc (direct cultent) motor. It mounts on a bracket secured to the radiator. A metal or plastic fan blade mounts on the end of the motor shaft to cause airflow. An electric fan saves energy and increases cooling system efficiency. Because it only functions when needed, it helps speed engine warm-up. This reduces emissions and fuel consumption. In cold weather, the electric fan may shut off at highway speeds. There may be enough cool air rushing through the grille to provide adequate cooling. Coolant still cold Temperature sending unit resistance high Thermo fan switch open A Temperature +-_.{.:j~::; sending unit resistance low Airflow through... radiator Gauge reads cold No current to fan motor Ijlll Battery _ Low current flow Gauge reads normal operating temperature increases Current flow to fan motor Thermo B switch closed Figure Study electric cooling fan operation. A-When the engine is cold, the thermo switch is open to prevent electric fan operation. This speeds engine warm-up. B-When the engine is at full operating temperature, the thermo switch closes. Current then flows to the fan motor to remove heat from the radiator. Electric Engine Fan Circuits The fan switch (thermo switch) is a temperaturesensitive switch that controls fan motor operation. With late-model vehicles, the coolant temperature sensor (switch), relays, and engine control module (or power train control module) operate the engine cooling fan motors, Figure When the engine is cold, the coolant sensor signals the ECM that the engine is cold. The ECM does not energize the fan relays. This keeps the cooling fan from spinning and speeds engine warm-up. After warm-up, the sensor resistance changes enough to signal the ECM of the need for cooling fan operation. The BCU sends current to the fan relay coils. This closes the relay contact, and high CUlTent flows to the cooling fans to prevent engine overheating. This is illustrated in Figure Radiator Shroud The radiator shroud helps ensure that the fan pulls air through the radiator. It fastens to the rear of the radiator and sultounds the area around the fan. See Figure When the fan is spinning, the plastic shroud keeps air from circulating between the back of the radiator and the front of the fan. As a result, a huge volume of air flows through the radiator core. Without a fan shroud, the engine could overheat. Thennostat The thermostat senses engine temperature and controls coolant flow through the radiator. It reduces coolant flow when the engine is cold and increases coolant flow when the engine is hot. The thermostat normally fits under a thermostat housing between the engine and the end of the upper radiator hose. Thermostats can be located at either the coolant inlet or outlet on the engine. The thermostat has a wax-filled pellet, Figure The pellet is contained in a cylinder-and-piston assembly. A spring holds the piston and valve in a normally closed position. When the thermostat is heated, the pellet expands and pushes the valve open. As the pellet and thermostat cool, spring tension overcomes pebet expansion and the valve closes. Figure shows the basic action of an engine thermostat. A thermostat rating is stamped on the thermostat to indicate the operating (opening) temperature of the thermostat. Normal ratings are between P and 195 P (82 C and 91 C). High thermostat heat ranges are used in

12 736 Section 6 Cooling and Lubrication Systems I Oldsmobile only IBuick only 840 ~ ",,;r-., Cooling fan I 5WHT 504 LH cooling 5 BLK 532 fan diode S , S141 5 Bt~ 5W~5~ LH cooling fan (primary) 35 OK BLU 473 P107 5 BLK LT BLU 409 RH cooling fan (secondary 5 BtK'i350 5 BLK r--1-.;:- ~ ~~--..I S G103 ~ ''11 Power train 'l--;,;,,;,; V8hIcIaapeed I :L. B 1:I - i - I law speed c:onifol 5V,_ high speed control Grouild I l : - - :.-~ I 452 ~ 35Y~W:O ' 35YE~1~!0 sensor Input. To connector See sequential ~~;, :L;;~ ~, "'c:;~' :: C101 terminal K7 F;;;;""---=;;; fuel injection _ /\"" (not used) See vehicle speed sensor + I B11 C101 [] ~~;I~~t [I:J ~~~~~t I S282 B A '- B A ' J41 temperature temperature.35 BLK 808 (ECT) sensor (ECT).5 BLK 452 sensor 5'"1 8 8LK,...I_:4_5_2 --I,,._.8_B_L_K_I_'4.J5; S126.35BL~ 808 A Y C.8LTGRN 36 I control I module I (PCM) Ground I ~ L!J ~ Figure This wiring diagram shows modern electric engine fan circuit controlled by an electronic control unit. Note how the engine coolant temperature sensor (bottom) signals the power train control module whether to turn fans on or off. To turn fans on, the ECU sends a low-current signal to relays. The relay contact points then close to send higher current to the fan motors.

13 Chapter 39 Cooling System Fundamentals 737 Radiator fan switch Fan Electric fan motor Ambient temperature sensing switch Fan shroud Coolant circulates through bypass and back into engine Engine cool thermostat closed A from engine Thermostat gasket Figure A fan shroud ensures that the fan pulls air through the radiator core. Without the shroud, air could circulate between the fan and the back of the radiator. Engine overheating could result. (DaimlerChrysler) Seal Wax-filled pellet Thermostat \ B Hot coolant from engine Engine hot, pellet expands to open thermostat Figure Study thermostat action. A-When coolant is cold, the thermostat remains closed due to spring tension. The water pump forces coolant to circulate in engine, but not through the radiator. B-When coolant is hot, the thermostat opens. The pump can then push coolant through the engine and the radiator. (DaimlerChrysler) Return spring Figure The thermostat is a temperature-sensitive valve. Note the pellet of wax enclosed in a cylinder-piston chamber. When heated, the pellet expands and pushes against spring tension to open the valve. (Gates) modem automobiles because they reduce exhaust emissions and increase combustion efficiency. Thermostat Operation When the engine is cold, the thermostat will be closed and coolant cannot circulate through the radiator. Instead, the coolant circulates around inside the engine block, cylinder head, and intake manifold until the engine is warm, Figure A. As the heat range of the thermostat is reached, the hot engine coolant causes the pellet inside the thermostat to expand. The thennostat gradually opens and allows coolant to flow through the system, Figure 39-27B. Since the amount of thermostat opening is dependent on engine temperature, the exact operating temperature of the engine can be precisely controlled. A bypass valve, Figure 39-28, and a bypass hose or passage permit coolant circulation through the engine when the thermostat is closed. If the coolant cannot circulate, hot spots could develop inside the engine. A bypass thermostat has a second valve for routing all the hot coolant through the radiator, not just most of the hot coolant. The main thermostat valve regulates flow through the engine and radiator like a conventional thermostat. The added valve blocks off the bypass once the engine has reached operating temperature. See Figure A thermostat jiggle valve is a small valve fit into a hole formed in the thermostat. It helps prevent air pockets from forming in the housing.

14 738 Section 6 Cooling and Lubrication Systems No flow to radiator Engine bypass open Fan off Thermostat closed r Thermostat open L c::::=: Water pump Heater hose Thermostat open Figure A bypass valve is sometimes used to allow circulation in the engine. It only opens when the thermostat is closed and when pressure is stronger than the bypass valve spring. Water pump drive pulley Figure Thermostat operation. A-The thermostat does not allow coolant to enter the radiator when the engine is below operating temperature. B-When the engine is at operating temperature, the thermostat opens and allows flow into radiator. The thermostat moves open and closed different amounts to maintain correct engine operating temperature. (OaimlerChrysler) Water pump housing flow Thermostat Cooling System Instrumentation Most vehicles are equipped with a temperature warning light. Some vehicles also have an engine temperature gauge. It is important that you understand the operation of both. Temperature Warning Light A temperature warning light informs the driver when the engine is overheating. When the coolant Figure This thermostat has a conventional valve and bypass valve on the body of the thermostat. Note that it has two springs and valves built into one assembly. (Cadillac) becomes too hot, a temperature sending unit (switch) in the engine block closes. This completes the warning light circuit, and the indicator light on the dash glows, Figure When the engine is cold or at normal operating temperature, the sending unit is open and the light remains off.

15 Chapter 39 Cooling System Fundamentals 739 Dash ~~~ning ~ / 4 amp fuse Yellow ~ Yellow - Violet ~ Splice > Red ~ Re _ Splice r!f /' Starter Ignition switch ~ lr / solenoid > ~Red-C: ~ Wale, lempe,a~!:i~ Batie" sending unit Prevents Winter Freeze Up Antifreeze keeps the coolant from freezing in very cold weather (outside temperature below 32 F or aoc). Coolant freezing can cause serious cooling system and engine damage. As ice forms, it expands. This expansion can produce great force. The water pump housing, cylinder head, engine block, radiator, or other parts could be cracked and ruined by this force. Prevents Rust and Corrosion Antifreeze also prevents rust and corrosion inside the cooling system. It provides a protective film on part surfaces, Figure Even in hot climates, antifreeze should be used to protect internal parts from corrosion. Figure The circuit diagram for a simple engine temperature warning light. The sending unit screws into the engine water jacket. It closes when the engine overheats to light indicator bulb. Ignition switch lights the bulb when the engine is started. This lets driver know the bulb is not burned out. (DaimlerChrysler) With many late-model vehicles, the engine temperature warning light is energized by the engine control module. If the sensor detects an overheating engine, the ECU sends current to the warning light. Engine Temperature Gauge An engine temperature gauge shows the exact operating temperature of the engine coolant. A variable resistance sending unit and a gauge are used in the circuit. When the engine is cold, the gauge sending unit has high resistance and current does not flow to the gauge. The temperature gauge reads cold. As engine temperature increases, the resistance in the sending unit drops. Current increases in the gauge circuit. Current causes the gauge needle to deflect to the right, showing engine temperature. Again, the engine control module often acts as an interface between the sending unit and the gauge. This was explained previously. Antifreeze Antifreeze, usually ethylene glycol, is mixed with water to produce engine coolant. Antifreeze has several functions. It prevents winter freeze up, prevents rust and corrosion, lubricates the water pump, and cools the engine. Figure Antifreeze protects internal parts from rust and corrosion. One example, when steel head gasket is coated with antifreeze (left), it is protected. With only water (right), rust occurs very quickly on the steel surface. (Fel-Pro) Lubricates the Water Pump Antifreeze acts as a lubricant for the water pump and thermostat. It increases the service life of the water pump bearings and seals. It also prevents thermostat wear and corrosion. Cools the Engine Antifreeze conducts heat better than water and, therefore, cools the engine better. It is normally recommended in hot weather. For example, using the air conditioning system increases the temperature of the air flowing through the radiator. Antifreeze can help prevent overheating in very hot weather when the air conditioning is on.

16 740 Section 6 Cooling and Lubrication Systems AntifreezelWater Mixture For ideal cooling and protection from freeze up, a 50/50 mixture of water and antifreeze is usually recommended. It will provide protection from ice formation to about -34 F (-37 C). Higher ratios of antifreeze may produce even lower freezing temperatures, but this much protection is not normally needed. Caution! Plain water should never be used in a cooling system or the four antifreeze functions just discussed will not be provided. Block Heater A block heater may be used on an engine to aid engine starting in cold weather. It is simply a l20-volt heating element mounted in the block water jacket. Look at Figure The heater power cord is plugged into a wall outlet. This keeps the engine warm when the vehicle is not being used. Then, when the owner cranks the engine, it wiu start more easily. A block heater is most commonly used on diesel engines. Diesels are harder to stmt in cold weather than gasoline engines because of their compression ignit,ion. Figure shows a cutaway of a diesel engine. Note the names of the cooling system parts. 120-volt power cord heater assambly Figure Block heaters plug into a home wall outlet. They heat coolant to aid starting in cold weather. Block heaters are common on diesel engines. (DaimlerChrysler) Hybrid Cooling The high current flowing through a hybrid vehicle's electric drive system can cause the drive system components to become extremely hot. In some hybrids, coolant is routed through the drive system components to carry heat back to the radiator for transfer to the atmosphere. In other hybrid vehicles, refrigerant is routed through the drive components to help keep them cool. Many hybrids use a blower and a system of ducts to route air around the high-voltage battery pack. The air helps cool the battery pack and remove dangerous hydrogen gases. Hybrid cooling was discussed in detail in Chapter 38, Hybrid Drive System Operation and Service. Airflow This hybrid vehicle uses a blower and ductwork to route cool passenger compartment air over the battery pack, where It picks up heat. The warm air Is then exhausted through the duct to the outside the vehicle. (Toyota)

17 Chapter 39 Cooling System Fundamentals 741 Thermostat Water pump pulley -- Water jackets Fan Crankshaft pulley Cylinder head Thermostat Cylinder block ----.::::"... Water jackets Figure Study the side and front views of this modern, four-cylinder, diesel engine. It uses an overhead camshaft to operate the valves. Also, note cooling system water jackets in the cylinder head and cylinder block. The thermostat is located at the front, center of engine. (Mercedes Benz)

18 742 Section 6 Cooling and Lubrication Systems Summary A cooling system must remove excess heat from the engine, maintain a constant engine operating temperature, increase the temperature of a cold engine quickly, and provide a means for warming the passenger compartment. Engine operating temperature is the temperature the engine coolant (water and antifreeze solution) reaches under normal running conditions. Typically, an engine's operating temperature is between 180 F and 210 F (82 C and 99 C). A liquid cooling system circulates a solution of water and antifreeze through the water jackets. In reverse flow cooling, cool coolant enters the head and hot coolant exits the block to return to the radiator. The water pump is an impeller or centrifugal pump that forces coolant through the engine block, cylinder head, intake manifold, hoses, and radiator. A water pump gasket fits between the engine and pump housing to prevent coolant leakage. Radiator hoses carry coolant between the engine water jackets and the radiator. Heater hoses are small diameter hoses that carry coolant to the heater core (small radiator-like device under the car dash). The radiator transfers coolant heat to the outside air. The radiator is normally mounted in front of the engine. A transmission oil cooler is often placed in the radiator on cars with automatic transmissions to prevent transmission fluid overheating. A closed cooling system uses an expansion tank, or reservoir, and a radiator cap with pressure and vacuum valves. A coohng system fan pulls air through the core of the radiator and over the engine to help remove heat. The thermostat senses engine temperature and controls coolant flow through the radiator. A thermostat rating is stamped on the thermostat to indicate the operating (opening) temperature of the thermostat. Normal ratings are between 180 F and 195 F (82 C and 91 C). Antifreeze, usually ethylene glycol, is mixed with water to produce the engine coolant. A block heater may be used on a diesel engine to aid engine starting in cold weather. Important Terms Cooling system Engine operating temperature Water pump Air cooling system Cooling fins Shrouds Liquid cooling system Conventional coolant flow Reverse flow cooling Radiator hoses Radiator Fan Thermostat Water pump impeller Water pump shaft Water pump seal Water pump bearings Water pump hub Water pump housing Water pump gasket Electric water pump Molded hose Flexible hose Hose spring Heater hoses Heater core Hose clamps Worm-drive hose clamp Radiator core Radiator tanks Radiator filler neck Radiator oil cooler Radiator petcock Downflow radiator Review Questions-Chapter 39 Crossflow radiator Radiator tanks Transmission oil cooler Radiator cap Radiator cap pressure valve Racliator cap pressure Radiator cap vacuum valve Closed cooling system Open cooling system Cooling system fan Engine-powered fan Fan spacer Flex fan Fluid coupling fan clutch Thermostatic fan clutch Electric cooling fan Fan motor Fan switch Thermo switch Coolant temperature sensor Radiator shroud Thermostat Thermostat rating Bypass valve Bypass thermostat Thermostat jiggle valve Temperature warning light Engine temperature gauge Antifreeze Block heater Please do not write in this text. Place your answers on a separate sheet of paper. 1. List and explain the five major parts of a cooling system. 2. What are the four functions of a cooling system? 3. Typically, an engine's operating temperature is between and OF ( and DC).

19 Chapter 39 Cooling System Fundamentals Not using a thermostat in hot weather is acceptable because the engine would run cooler. True or False? 5. Why has the liquid cooling system replaced the air types? 6. List and explain the six major palts of a water pump. 7. Which of the following does not relate to radiator construction? (A) Core. (B) Filler neck. (C) Tanks. (D) Impeller. 8. Explain the differences between downflow and crossflow radiators. 9. How does an automatic transmission oil cooler work? 10. Desclibe the four functions of a radiator cap. 11. Typical radiator cap pressure is to psi ( to kpa), which raises the boiling point of the coolant to about to QF ( to QC). 12. How do closed and open cooling systems differ? 13. A(n) is commonly used to tum an electric engine cooling fan on and off. 14. Summarize the operation of a cooling system thermostat. 15. Why is a radiator shroud used? 16. A temperature (switch) on the engine is used to operate the temperature warning light. 17. List and explain four reasons why antifreeze should be used in the cooling system. 18. For ideal cooling, this mixture of water and antifreeze is typical. (A) 30% water, 70% antifreeze. (B) 50% water, 50% antifreeze. (C) 80% antifreeze, 20% water. (D) 70% water, 30% antifreeze. 19. Why could a block heater be helpful with a diesel engine? 20. Should plain water (no antifreeze) be used in a cooling system duling warm weather? Why? ASE-Type Q estions 1. Which of the following system parts controls coolant flow? (A) Fan. (B) Radiator. (C) Thermostat. (D) Temperature sensor. 2. An engine's operating temperature is usually between: (A) 8rF and 99 F (B) loo F and 120 F (C) 125 F and 150 F (D) 180 F and 210 F 3. A water pump normally mounts: (A) under the engine. (B) on the back ojthe engine. (C) on the front ojthe engine. (D) Any oj the above. 4. Which of the following may be used to prevent coolant leakage between the water pump housing and engine? (A) Gasket. (B) RTV sealer. (C) O-ring seal. (D) None ojthe above. 5. Each of the following is a radiator component except: (A) core (B) petcock. (C) oil cooler. (D) bypass valve. 6. Which of the following is not a radiator cap function? (A) Absorb heat. (B) Seal radiator top. (C) Pressurize system. (D) Relieve excess pressure. 7. Which fan type is used on front-wheel-drive cars with transverse engines? (A) Flexible Jan. (B) Electric engine Jan. (C) Engine-poweredJan, (D) None of the above.

20 744 Section 6 Cooling and Lubrication Systems 8. Which of the following controls coolant flow Activities-Chapter 39 through a radiator? (A) Shroud. (B) Fan switch. (e) Thermostat. (D) Temperature senso,: 9. When a thermostat is closed, which of these permits coolant circulation through the engine? (A) Bypass hose. (B) Bypass valve. (e) Both ojthe above. (D) None ofthe above. 10. Antifreeze serves each of these functions except: (A) lubricate water pump. (B) prevent winterjreeze up. (e) prevent rust and corrosion. (D) control engine temperature. l. Using the infonnation contained in the chart on most antifreeze containers, construct a line graph to show the relationship between water! antifreeze mixture and the low-temperature protection provided. (For example, the usual 50/50 mixture protects against freezing to temperatures as low as -34 F.) 2. Develop sketches to show how the expansion tank (coolant reservoir) functions in a closed cooling system. Make overhead transparencies from your sketches and use them to describe the expansion tank function to the class.