The following methods are currently being employed for this:
l. The fan blades are of variable pitch type, which is controlled by the engine speed itself. As the engine speed increases, the pitch decreases, thus reducing the air flow. Alternatively, the blade pitch is controlled directly by the cooling water temperature, which has been found to be more efficient design.
2. The fan is not directly driven by the belt from the crankshaft, but is driven through a fluid coupling. One rotor of the coupling is driven by the engine, while to the other one is attached the fan. The spacing between the rotors is controlled by the temperature of the cooling system, which changes the slip of the coupling thus changing the fan speed according to the
requirements.
3. The fan is driven by means of a separate electric motor which is supplied with power directly from the electric circuit of the engine. This system has been used on Maruti cars. A thermostat switch is placed at an appropriate place in the cooling system and depending upon the cooling
system temperature it operates to switch on or off the fan motor. It has been found that under ordinary conditions, only about 5 percent of the time the fan motor remains in ‘on’ position, while 95 per cent of the time it is ‘off.’ The saving of engine power thus achieved may, therefore, be well imagined.
Check the cooling fan. If the vehicle is equipped with a centrifugal thermo-static type fan clutch, it is important to spot problems before they occur. Check for wear by moving the fan blade back and forth. Over 1/4" of play in either direction could point towards excessive bearing wear. You should also turn the fan by hand. If it free-wheels or there is a rough grating feel as the fan turns, this could mean excessive fluid loss or bearing wear respectively. If any of these conditions exist or there is evidence of fluid leakage, the fan clutch should be replaced. If the vehicle is equipped with an electric cooling fan, a quick performance check can be made by turning on the A/C and checking to make sure it operates without excess vibration or noise. Also check all electrical connections for signs of corrosion, or physical damage. With the engine hot, check to see if the fan is coming on at the correct temperature and operating properly.
Checking Fans and Fan Clutches
Fan operation can be checked by spinning the fan by hand. A noticeable wobble or any-blade that is not in the same plane as the rest indicates that replacement is in order. The fan can also be checked by removing it and laying it on a flat surface. If it is straight, all the blades should touch the surface. Never attempt to straighten a damaged cooling fan. Bending it back into shape might seem easier (and cheaper) than replacing it, but doing so is risky. Whenever metal is bent, it is weakened Fan clutches use a fluid-filled chamber (usually silicone) to turn the fan. Obviously, loss of the drive fluid will render the fan useless. One of the simplest checks is to visually inspect the fan clutch for signs of fluid loss. Oily streaks radiating outward from the hub shaft mean fluid has leaked out past the bearing seal.
Most fan clutches offer a slight amount of resistance if turned by hand when the engine is cold. They offer drag when the engine is hot. If the fan freewheels easily hot or cold, replace the clutch. Another check that should be made is to push the tip of a fan blade in and out. Any visible looseness in the shaft bearing means the fan clutch should be replaced. Fan blades are balanced at the time of manufacture but can be bent if handled carelessly. Likewise, fan clutches are machined very accurately to run true. However, rough handling at the time of pump replacement causes nicks and dents on the mounting faces. This can cause the fan blade to be installed crookedly. Serious trouble might follow soon after the car is back in service. There-
fore, technicians should be cautioned to handle fan clutches and blades with care and to file away any nicks, burrs, or dents someone else might have caused. Obviously, if any fins have been broken off the fan clutch, it
must be replaced.
Checking Belts
If a belt breaks, at best the fan stops spinning and the coolant does not cool down efficiently. At worst, the water pump stops, the coolant does not circulate, and, eventually, the engine overheats. Belts, like hoses, are made of elastic rubber compounds. Although they are extremely sturdy, they are primarily designed for transmitting power. Even the best belts last only an average of four years. Advise the customer to replace all belts every four years, regardless of how they look. Fortunately, belt problems are easily discovered either by visual inspection for cracks, splits, glazing, or oil soak-age, or by the screech of slippage. In servicing a multi-belt setup, it is very important to replace all of the belts when one belt is bad. The mounting brackets on generators, power-steering pumps, and air compressors are designed to be adjustable so proper tension can be maintained on these belts. Some of these brackets have a hole or slot to allow the use of a pry bar or wrench when adjusting. Some automobiles require the fan, fan pulley, and other accessory drive belts to be removed to gain access to belts needing replacement. Always use the exact replacement size of belt. The size of a new belt is typically given, along with the part number, on the belt container. After replacing a belt, make sure it is adjusted properly. Some engines have an adjusting bolt that can be tightened to bring the belt tension to specifications. On other engines, it may be necessary to use a pry bar to move an accessory enough to meet tension specs. Be careful not to damage the part you are prying against. The belt’s tension should be checked with a belt tension gauge. When installing a serpentine belt, make sure it is fed in and around the accessories properly. Service manuals
show the proper belt routing. Also make sure the belt tensioner is working properly. After any drive belt has been installed with the correct tension, tighten any bolts or nuts that were loosened to move the belt. Misalignment of the V-pulleys reduces the belt’s service life and brings about rapid V-pulley wear. Undesirable side or end thrust loads can also be imposed on pulley or pump shaft bearings. It is important to check alignment by using a straightedge. Pulleys should be in alignment within 1/16 inch (1.59 mm) per foot of the distance across the face of the pulleys.
FLUSHING COOLING SYSTEM
Rust and scale will inevitably form in any cooling system. When they do, there are a few vulnerable places they can attack. One happens to be the main seal in the water pump, which keeps coolant away from the bearing and its lubricant. If grit is allowed to erode the seal, the bearing will be the next item to go. Coolant leaking from the water pump's vent hole is evidence of seal failure. Whenever coolant is changed, and especially before a water pump is replaced, a thorough reverse flushing or back flushing should be performed. Before this flushing is done, chemical cleaners can be added to the cooling system to help dissolve rust and scale deposits. Reverse flushing is the procedure of forcing clean liquid backwards through the cooling system. This carries away rust, scale, corrosion, and other contaminants. A flushing gun that operates on compressed air is used to force clean water and air through the system. This method of flushing the system is not recommended on systems that use plastic and aluminum radiators. Check the service manual for the proper way of cleaning out the cooling system on vehicles with those kinds of radiators.
Refilling and Bleeding
After the cooling system has been cleaned, refill the system with new coolant mixed to the recommend-ed strength. Be sure all the flushing water is out of the radiator and evacuated from the engine block before refilling.
The cooling system must be bled to ensure there are no air pockets in the coolant. Air in the system can reduce cooling ability and lead to water pump and other component damage. Each vehicle has its own specific bleeding procedure. In-many cases, the system are filled and the radiator cap is left off. The engine is then run until the thermostat opens and the coolant circulates. Tapped air bubbles escape through the opened radiator. Other bleeding procedures are more involved. They may require the connection of special bleeder hoses to air bleed valves located on the radiator or other components. Air is bled through the valves as the system is filled. Always follow the bleeding steps outlined in the vehicle’s service manual.
COOLANT PUMP
A coolant pump is a necessity for the forced circulation type of engine cooling system. The pump is mounted at the front end of the engine and is driven from the crankshaft by means of a V- belt. Centrifugal type pump is the one which is used for this purpose (5.14). The coolant from the radiator enters the pump at the centre where inlet is located. The flow of the coolant
depends upon the pump speed which is proportional to engine speed, This is desirable since at higher engine speeds more heat is developed which requires more cooling. The scroll is connected to the front of the engine to direct the coolant into the block. For V-engine the coolant pump has two outlets, one for each bank of cylinders.
components of a coolant pump.
The main parts of the pump are a casing
(l) and a shaft-mounted impeller
(2) having a number of vanes. The impeller shaft is mounted on bearing
(3) while the seal
(4) serves to prevent the leakage of coolant around the shaft.
When the impeller rotates, the coolant between the vanes is thrown outward due to the centrifugal force, thus forcing the cooled coolant at the periphery, with a force depending upon the speed of rotation of the pump spindle, which itself is proportional to the engine speed .This water leaving the periphery of the impeller tangentially and having maximum kinetic energy then enters the in volute or the scroll, which is a smoothly curved passage cast in the casing, whose cross-sectional area gradually increases towards the outlet port. Thus the enlarging scroll converts the kinetic energy of coolant to pressure energy. In this way a coolant pressure is created at the pump outlet that forces the coolant through the cooling system.
l. The fan blades are of variable pitch type, which is controlled by the engine speed itself. As the engine speed increases, the pitch decreases, thus reducing the air flow. Alternatively, the blade pitch is controlled directly by the cooling water temperature, which has been found to be more efficient design.
2. The fan is not directly driven by the belt from the crankshaft, but is driven through a fluid coupling. One rotor of the coupling is driven by the engine, while to the other one is attached the fan. The spacing between the rotors is controlled by the temperature of the cooling system, which changes the slip of the coupling thus changing the fan speed according to the
requirements.
3. The fan is driven by means of a separate electric motor which is supplied with power directly from the electric circuit of the engine. This system has been used on Maruti cars. A thermostat switch is placed at an appropriate place in the cooling system and depending upon the cooling
system temperature it operates to switch on or off the fan motor. It has been found that under ordinary conditions, only about 5 percent of the time the fan motor remains in ‘on’ position, while 95 per cent of the time it is ‘off.’ The saving of engine power thus achieved may, therefore, be well imagined.
Check the cooling fan. If the vehicle is equipped with a centrifugal thermo-static type fan clutch, it is important to spot problems before they occur. Check for wear by moving the fan blade back and forth. Over 1/4" of play in either direction could point towards excessive bearing wear. You should also turn the fan by hand. If it free-wheels or there is a rough grating feel as the fan turns, this could mean excessive fluid loss or bearing wear respectively. If any of these conditions exist or there is evidence of fluid leakage, the fan clutch should be replaced. If the vehicle is equipped with an electric cooling fan, a quick performance check can be made by turning on the A/C and checking to make sure it operates without excess vibration or noise. Also check all electrical connections for signs of corrosion, or physical damage. With the engine hot, check to see if the fan is coming on at the correct temperature and operating properly.
Checking Fans and Fan Clutches
Fan operation can be checked by spinning the fan by hand. A noticeable wobble or any-blade that is not in the same plane as the rest indicates that replacement is in order. The fan can also be checked by removing it and laying it on a flat surface. If it is straight, all the blades should touch the surface. Never attempt to straighten a damaged cooling fan. Bending it back into shape might seem easier (and cheaper) than replacing it, but doing so is risky. Whenever metal is bent, it is weakened Fan clutches use a fluid-filled chamber (usually silicone) to turn the fan. Obviously, loss of the drive fluid will render the fan useless. One of the simplest checks is to visually inspect the fan clutch for signs of fluid loss. Oily streaks radiating outward from the hub shaft mean fluid has leaked out past the bearing seal.
Most fan clutches offer a slight amount of resistance if turned by hand when the engine is cold. They offer drag when the engine is hot. If the fan freewheels easily hot or cold, replace the clutch. Another check that should be made is to push the tip of a fan blade in and out. Any visible looseness in the shaft bearing means the fan clutch should be replaced. Fan blades are balanced at the time of manufacture but can be bent if handled carelessly. Likewise, fan clutches are machined very accurately to run true. However, rough handling at the time of pump replacement causes nicks and dents on the mounting faces. This can cause the fan blade to be installed crookedly. Serious trouble might follow soon after the car is back in service. There-
fore, technicians should be cautioned to handle fan clutches and blades with care and to file away any nicks, burrs, or dents someone else might have caused. Obviously, if any fins have been broken off the fan clutch, it
must be replaced.
Checking Belts
If a belt breaks, at best the fan stops spinning and the coolant does not cool down efficiently. At worst, the water pump stops, the coolant does not circulate, and, eventually, the engine overheats. Belts, like hoses, are made of elastic rubber compounds. Although they are extremely sturdy, they are primarily designed for transmitting power. Even the best belts last only an average of four years. Advise the customer to replace all belts every four years, regardless of how they look. Fortunately, belt problems are easily discovered either by visual inspection for cracks, splits, glazing, or oil soak-age, or by the screech of slippage. In servicing a multi-belt setup, it is very important to replace all of the belts when one belt is bad. The mounting brackets on generators, power-steering pumps, and air compressors are designed to be adjustable so proper tension can be maintained on these belts. Some of these brackets have a hole or slot to allow the use of a pry bar or wrench when adjusting. Some automobiles require the fan, fan pulley, and other accessory drive belts to be removed to gain access to belts needing replacement. Always use the exact replacement size of belt. The size of a new belt is typically given, along with the part number, on the belt container. After replacing a belt, make sure it is adjusted properly. Some engines have an adjusting bolt that can be tightened to bring the belt tension to specifications. On other engines, it may be necessary to use a pry bar to move an accessory enough to meet tension specs. Be careful not to damage the part you are prying against. The belt’s tension should be checked with a belt tension gauge. When installing a serpentine belt, make sure it is fed in and around the accessories properly. Service manuals
show the proper belt routing. Also make sure the belt tensioner is working properly. After any drive belt has been installed with the correct tension, tighten any bolts or nuts that were loosened to move the belt. Misalignment of the V-pulleys reduces the belt’s service life and brings about rapid V-pulley wear. Undesirable side or end thrust loads can also be imposed on pulley or pump shaft bearings. It is important to check alignment by using a straightedge. Pulleys should be in alignment within 1/16 inch (1.59 mm) per foot of the distance across the face of the pulleys.
FLUSHING COOLING SYSTEM
Rust and scale will inevitably form in any cooling system. When they do, there are a few vulnerable places they can attack. One happens to be the main seal in the water pump, which keeps coolant away from the bearing and its lubricant. If grit is allowed to erode the seal, the bearing will be the next item to go. Coolant leaking from the water pump's vent hole is evidence of seal failure. Whenever coolant is changed, and especially before a water pump is replaced, a thorough reverse flushing or back flushing should be performed. Before this flushing is done, chemical cleaners can be added to the cooling system to help dissolve rust and scale deposits. Reverse flushing is the procedure of forcing clean liquid backwards through the cooling system. This carries away rust, scale, corrosion, and other contaminants. A flushing gun that operates on compressed air is used to force clean water and air through the system. This method of flushing the system is not recommended on systems that use plastic and aluminum radiators. Check the service manual for the proper way of cleaning out the cooling system on vehicles with those kinds of radiators.
Refilling and Bleeding
After the cooling system has been cleaned, refill the system with new coolant mixed to the recommend-ed strength. Be sure all the flushing water is out of the radiator and evacuated from the engine block before refilling.
The cooling system must be bled to ensure there are no air pockets in the coolant. Air in the system can reduce cooling ability and lead to water pump and other component damage. Each vehicle has its own specific bleeding procedure. In-many cases, the system are filled and the radiator cap is left off. The engine is then run until the thermostat opens and the coolant circulates. Tapped air bubbles escape through the opened radiator. Other bleeding procedures are more involved. They may require the connection of special bleeder hoses to air bleed valves located on the radiator or other components. Air is bled through the valves as the system is filled. Always follow the bleeding steps outlined in the vehicle’s service manual.
COOLANT PUMP
A coolant pump is a necessity for the forced circulation type of engine cooling system. The pump is mounted at the front end of the engine and is driven from the crankshaft by means of a V- belt. Centrifugal type pump is the one which is used for this purpose (5.14). The coolant from the radiator enters the pump at the centre where inlet is located. The flow of the coolant
depends upon the pump speed which is proportional to engine speed, This is desirable since at higher engine speeds more heat is developed which requires more cooling. The scroll is connected to the front of the engine to direct the coolant into the block. For V-engine the coolant pump has two outlets, one for each bank of cylinders.
components of a coolant pump.
The main parts of the pump are a casing
(l) and a shaft-mounted impeller
(2) having a number of vanes. The impeller shaft is mounted on bearing
(3) while the seal
(4) serves to prevent the leakage of coolant around the shaft.
When the impeller rotates, the coolant between the vanes is thrown outward due to the centrifugal force, thus forcing the cooled coolant at the periphery, with a force depending upon the speed of rotation of the pump spindle, which itself is proportional to the engine speed .This water leaving the periphery of the impeller tangentially and having maximum kinetic energy then enters the in volute or the scroll, which is a smoothly curved passage cast in the casing, whose cross-sectional area gradually increases towards the outlet port. Thus the enlarging scroll converts the kinetic energy of coolant to pressure energy. In this way a coolant pressure is created at the pump outlet that forces the coolant through the cooling system.
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