Different types of coolant pumps
The present trend is to make coolant pumps smaller and lighter. Light alloys are increasingly being used for pump bodies while use of synthetic resins is on increase for impellers. The shaft- bearing design in which shaft and bearings are combined in one unit has resulted in more compact design.
Thermo-responsive Coolant Pump
M/s Thompson Products Inc. (U.S.A.) have devised a pump with which the circulation of coolant is directly controlled by means of metallic vanes on the impeller, instead of by the use of thermostat valve. Bimetallic elements are provided on the periphery of the impeller. These elements control the apertures on the periphery of the impeller. under low temperature conditions the elements close the apertures and there is no pumping action. However, as the coolant temperature increases the elements deflect to open the apertures and the pump discharges coolant into circulation.
Check the radiator cap. If your cap is rusted or the rubber seal is dried out, it should be replaced. A pressure tester should be used to be sure the cap is operating at the recommended pressure level.
COOLING SYSTEM TROUBLE SHOOTING
The common faults occurring in the cooling system are described below. Along with their possible causes and suitable remedies.
1. Overheating. This may be caused due to any one or more of the following reasons. However, it must be borne in mind that the overheating is caused not only due to defects in the cooling system. Rather the same may be caused by many factors completely different. i.e., pertaining to other systems also, e.g., too much retarded ignition timing, weak air-fuel mixture etc. Check for internal leaks. Pull the oil dipstick and check for evidence of coolant. It will show up as minute droplets or sludge and should be easy to spot. This could indicate a cracked head, block or blown head gasket.
(i) Accumulation of rust or scale in the coolant jackets and the radiator. Rust and scale are both bad thermal conductors and thus the rate of heat transfer is decreased. This may be remedied by use of suitable chemicals (e.g ordinary washing soda) and reverse flushing. Reverse flushing is done by circulating water under pressure in the direction opposite to the normal. This is done with the help of special air pressure gun which forces the water through. Flushing of the engine and the radiator is done separately. The effect of the chemical is to loosen the scale and the reverse flushing then washes it away. An important precaution is to use only warm water for flushing a warm engine. In some cases the reverse flushing may cause damage to the engine. So before resorting to this, the manufacturer's manual must be studied.
(ii) Defective hose or faulty connections may be another source of overheating. Defective hose may become a source of the hose material accumulating in the radiator passages or engine water jackets while the faulty connections will cause leaking of coolant thus reducing the capacity of the cooling system to extract heat. The remedy is to replace the defective hose and to tighten the various connections, so that there is no more any leakage.
(iii) Sometimes the engine block may also be cracked, causing loss of coolant. This can be tested by plugging coolant inlet and outlet and pumping in the water under pressure. If the block is found cracked, the same may be suitably repaired.
(iv) Defective coolant pump reduces the volume of the coolant to be circulated and thus may be the cause of overheating. There is no definite method to test the coolant pump. However, if the upper hose is opened out and hand is placed over the water jacket outlet while the engine is running, then the feeling of some pressure (which one knows by experience) by the hand indicates that coolant pump is functioning normally. If it is not functioning properly, open it out and look for the defects, which may be
corrected.
Check the thermostat: Remove the radiator cap and start the engine. Insert a suitable thermometer into the radiator neck. When the coolant level drops in the radiator, the thermostat has opened and is allowing circulation. Record the temperature on the thermometer and compare to the thermostat specifications. It should be no more than a few degrees either way of the actual thermostat setting. If you are not in the correct range, the thermostat will have to be replaced. Be sure to install a new gasket and inspect the thermostat seating area for corrosion and pitting.
(v) A defective thermostat that may be sticking in the closed position will not allow the coolant to go to the radiator and be cooled there. As a result the engine will be overheated. The thermostat valve may be tested by taking it out and placing it in a hot water bath in which the thermometer is also placed. If the valve opens and closes at the same temperatures as specified in the manufacturer’s manual, it is alright; otherwise it is defective. The remedy in this case is to replace it.
(vi) Fan belt which is slipping may be another source of engine overheating. The slipping may be either due to the belt being loose or by the oiling of the belt or any of the pulleys. A loose belt may be tested by pressing it at the centre with hand. If the belt sags by more than 10- 15 mm with a force of 30-40 N, it is definitely loose and needs tightening, which is done by shifting the generator and retightening its belts. In MM-540 DP jeep the belt is tightened by screwing to bring index (3) in front of face (a) of flange marking. The oiled belt or pulleys should be cleaned with a piece of cloth. If the belt is otherwise defective, it should be replaced atonce.
(vii) The air passages in the radiator may be blocked. These may be opened up by blowing air under pressure from the fan side of the radiator. The fins of the radiator may also be damaged so as to obstruct the flow of air. The same may be corrected with pliers or screw driver.
(viii) Loss of coolant by evaporation may also be a cause of overheating, which may be corrected by filling the radiator to the correct level.
(ix) Radiator fan thermostat switch, if provided, may be defective. This can be tested by immersing the switch in hot water and testing its continuity If the switch conducts when the h6t water temperature rises to 86-90°C and it does not when the hot water temperature falls down to 81-85°C, it is in good condition. If found defective, the switch should be replaced.
2. Slow warm up (or overcooling). When the engine takes unduly more time to warm, defect may be also due to the thermostat valve being stuck open. It may be removed and tested. If found defective, the same has to be replaced.
3. Noisy coolant pump. If the coolant pump is making too much noise, the reason may be either defective seal or defective bearing. The only remedy is the replacement of the faulty components.
The present trend is to make coolant pumps smaller and lighter. Light alloys are increasingly being used for pump bodies while use of synthetic resins is on increase for impellers. The shaft- bearing design in which shaft and bearings are combined in one unit has resulted in more compact design.
Thermo-responsive Coolant Pump
M/s Thompson Products Inc. (U.S.A.) have devised a pump with which the circulation of coolant is directly controlled by means of metallic vanes on the impeller, instead of by the use of thermostat valve. Bimetallic elements are provided on the periphery of the impeller. These elements control the apertures on the periphery of the impeller. under low temperature conditions the elements close the apertures and there is no pumping action. However, as the coolant temperature increases the elements deflect to open the apertures and the pump discharges coolant into circulation.
Check the radiator cap. If your cap is rusted or the rubber seal is dried out, it should be replaced. A pressure tester should be used to be sure the cap is operating at the recommended pressure level.
COOLING SYSTEM TROUBLE SHOOTING
The common faults occurring in the cooling system are described below. Along with their possible causes and suitable remedies.
1. Overheating. This may be caused due to any one or more of the following reasons. However, it must be borne in mind that the overheating is caused not only due to defects in the cooling system. Rather the same may be caused by many factors completely different. i.e., pertaining to other systems also, e.g., too much retarded ignition timing, weak air-fuel mixture etc. Check for internal leaks. Pull the oil dipstick and check for evidence of coolant. It will show up as minute droplets or sludge and should be easy to spot. This could indicate a cracked head, block or blown head gasket.
(i) Accumulation of rust or scale in the coolant jackets and the radiator. Rust and scale are both bad thermal conductors and thus the rate of heat transfer is decreased. This may be remedied by use of suitable chemicals (e.g ordinary washing soda) and reverse flushing. Reverse flushing is done by circulating water under pressure in the direction opposite to the normal. This is done with the help of special air pressure gun which forces the water through. Flushing of the engine and the radiator is done separately. The effect of the chemical is to loosen the scale and the reverse flushing then washes it away. An important precaution is to use only warm water for flushing a warm engine. In some cases the reverse flushing may cause damage to the engine. So before resorting to this, the manufacturer's manual must be studied.
(ii) Defective hose or faulty connections may be another source of overheating. Defective hose may become a source of the hose material accumulating in the radiator passages or engine water jackets while the faulty connections will cause leaking of coolant thus reducing the capacity of the cooling system to extract heat. The remedy is to replace the defective hose and to tighten the various connections, so that there is no more any leakage.
(iii) Sometimes the engine block may also be cracked, causing loss of coolant. This can be tested by plugging coolant inlet and outlet and pumping in the water under pressure. If the block is found cracked, the same may be suitably repaired.
(iv) Defective coolant pump reduces the volume of the coolant to be circulated and thus may be the cause of overheating. There is no definite method to test the coolant pump. However, if the upper hose is opened out and hand is placed over the water jacket outlet while the engine is running, then the feeling of some pressure (which one knows by experience) by the hand indicates that coolant pump is functioning normally. If it is not functioning properly, open it out and look for the defects, which may be
corrected.
Check the thermostat: Remove the radiator cap and start the engine. Insert a suitable thermometer into the radiator neck. When the coolant level drops in the radiator, the thermostat has opened and is allowing circulation. Record the temperature on the thermometer and compare to the thermostat specifications. It should be no more than a few degrees either way of the actual thermostat setting. If you are not in the correct range, the thermostat will have to be replaced. Be sure to install a new gasket and inspect the thermostat seating area for corrosion and pitting.
(v) A defective thermostat that may be sticking in the closed position will not allow the coolant to go to the radiator and be cooled there. As a result the engine will be overheated. The thermostat valve may be tested by taking it out and placing it in a hot water bath in which the thermometer is also placed. If the valve opens and closes at the same temperatures as specified in the manufacturer’s manual, it is alright; otherwise it is defective. The remedy in this case is to replace it.
(vi) Fan belt which is slipping may be another source of engine overheating. The slipping may be either due to the belt being loose or by the oiling of the belt or any of the pulleys. A loose belt may be tested by pressing it at the centre with hand. If the belt sags by more than 10- 15 mm with a force of 30-40 N, it is definitely loose and needs tightening, which is done by shifting the generator and retightening its belts. In MM-540 DP jeep the belt is tightened by screwing to bring index (3) in front of face (a) of flange marking. The oiled belt or pulleys should be cleaned with a piece of cloth. If the belt is otherwise defective, it should be replaced atonce.
(vii) The air passages in the radiator may be blocked. These may be opened up by blowing air under pressure from the fan side of the radiator. The fins of the radiator may also be damaged so as to obstruct the flow of air. The same may be corrected with pliers or screw driver.
(viii) Loss of coolant by evaporation may also be a cause of overheating, which may be corrected by filling the radiator to the correct level.
(ix) Radiator fan thermostat switch, if provided, may be defective. This can be tested by immersing the switch in hot water and testing its continuity If the switch conducts when the h6t water temperature rises to 86-90°C and it does not when the hot water temperature falls down to 81-85°C, it is in good condition. If found defective, the switch should be replaced.
2. Slow warm up (or overcooling). When the engine takes unduly more time to warm, defect may be also due to the thermostat valve being stuck open. It may be removed and tested. If found defective, the same has to be replaced.
3. Noisy coolant pump. If the coolant pump is making too much noise, the reason may be either defective seal or defective bearing. The only remedy is the replacement of the faulty components.
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Coolant pump
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