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kap all phase & 6/11/03 11:35 am Page Student Workbook LV21 Cooling Systems (2) LV21/SWB Student Workbook for Technical Certificates in Light Vehicle Maintenance and Repair MODULE LV21 COOLING SYSTEMS (2) Contents Page Page … Common Faults Associated with Cooling Systems Overheating: Visible signs of overheating What to check Radiator Radiator cap Thermostat Cooling fans Fan belt Modern ribbed fan belt Water pump Hoses Air lock Cylinder head gasket Progress check 4 5 8 9 10 Overcooling: Water loss Condition of coolant Safety first Progress check 12 12 13 15 16 Cooling and Heater System: Exercise Layout of a cooling system Inspect rubber hoses Coolant level Servicing Draining and refilling the cooling system 17 17 17 18 18 18 Flushing the cooling system Removing and flushing the expansion tank Refilling the cooling system Bleeding the system Exercise Exercise Exercise Ventilation and Heater Systems: Ventilator Natural air ventilation Forced air ventilation Heater system Heating and ventilation (slider controls) Rotary control knobs Detailed operation of the heater system Exercise Heater mode Bi-level mode Defroster mode Ventilation mode Vehicle heating systems – trouble shooting 19 -1Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue 20 21 21 22 23 24 25 26 26 26 27 27 28 29 30 31 31 32 32 32 33 -2Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Common Faults Associated with Cooling Systems The cooling system of a motor vehicle is designed to dissipate thermal energy, produced by combustion from the engine Heat is also produced by friction, engine oil plays its part by reducing friction and dissipating heat The cooling system prevents the engine from seizing by using a liquid coolant (a mixture of antifreeze and water), which is circulated around the engine cylinder block, head and radiator where air is used to disperse the heat into the atmosphere If the cooling system malfunctions, because of e.g a blockage in the radiator, loss of coolant or a thermostat fails to operate properly or the fan belt becomes slack the engine is certain to overheat Sometimes an engine can overcool, this can be caused by an electric fan thermostat switch not functioning properly e.g when it does not switch the cooling fan off when the engine is cool Temperature switches operate by using a bi-metallic strip, which consists of two dissimilar metals side by side, when heated the strip bends, electrical contacts then open and a relay switches on the fan Recommended website http://www.howstuffworks.com/index.htm -3Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Overheating An overheated engine is the most common fault, it can be caused simply by loss of coolant A low coolant level due to lack of regular maintenance can lead to an expensive engine problem Visible signs of overheating Normal running temperature Engine temperature Ambient air temperature Signs of overheating: • escaping steam • hot smell or an odour of antifreeze • temperature gauge on the instrument panel showing higher temperature than normal Some engines may run more noisily or may not run as smoothly in extreme cases of overheating Note: Temperature gauge may be displaying an incorrect temperature due to a fault or the sender unit itself may be at fault -4Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue What to check Radiator Rust coloured sediment blocking the tubes The inside of the radiator can become blocked with a build-up of sediment If the radiator is not serviced this build up impedes the flow of coolant and reduces the efficiency of the cooling system Flushing the radiator is recommended, usually back or reverse flushing should solve the problem The cooling system is one of the most neglected systems Regular servicing reduces the likelihood of blockages occurring The radiator requires checking during servicing for debris that has built up on the cooling fins, such as leaves or paper etc which would restrict the air-flow through the fins Radiator cap If the radiator cap is not ‘sealing in’ the pressure it can lead to a rise in temperature Remember from Phase Cooling Systems LV08, increasing the coolant pressure raises its boiling point and conversely a lower pressure lowers the boiling point Most engines run near the boiling point of water, therefore, if the pressure in the cooling system falls, then it is more likely to cause the coolant to boil -5Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue New radiator cap This seal is very worn Pressure seal Vacuum valve The cooling system is pressurised to raise the boiling point of the coolant (most liquids boil at a higher temperature when subjected to a pressure increase) A cooling system can operate at higher temperatures if it is pressurised before it can begin to turn to steam, cooling system components are manufactured strongly enough to operate at these pressures The seal on the bottom of the radiator cap is most likely to become worn or deteriorate due to long service and this would lower the operating pressure of the cooling system If the vacuum valve stuck it would cause the hoses to collapse and possibly the radiator, due to atmospheric pressure acting on them The operating pressure of the cooling system is stamped on the radiator cap, the operating pressure of the cap can be checked using a pressure tester This is a hand pump which has a pressure gauge fitted to establish whether the cap is holding pressure at its rated specification Thermostat The thermostat is a key component in the cooling system, it may fail to operate in a ‘stuck open’ or ‘stuck closed’ condition The thermostat can be checked after removal from the cooling system by placing it in a container of water alongside a thermometer, the water is then heated and the temperature at which the thermostat opens can be recorded and compared with the manufacturers’ specifications (stamped on the thermostat) When the thermostat is slow to open or is ‘stuck closed’, overheating will be experienced -6Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Cooling fans Image with fan removed Cooling fans play an essential role when the vehicle is stationary or moving slowly in traffic, they may be mechanical (driven by a fan belt) electric or viscous Electric or viscous fans, the most popular nowadays, operate at a certain temperature to prevent the engine overheating whilst providing a more rapid warm-up and good engine temperature control X Hot – open circuit Cold – closed circuit Some vehicles often have their fans operated by an electronic control unit (ECU) When electric fans fail to operate - fuses, relays, temperature sensor and supply current must be checked Above is a simple electrically operated fan circuit -7Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Fan belt Fan belts require periodic examination for wear and correct tension A fan belt may break or become worn making it ineffective for rotating the pump A noisy fan belt is a symptom of slipping and it is usually best in this case to replace the belt rather than adjusting it because it is likely to be badly worn due to slipping Modern ribbed fan belt Water pump Impeller Coolant leaks from here when the pump seal or bearing is worn Cracked flange Some water pumps have a plastic impeller that may shear off, although the pump is turning there would be no coolant circulated around the system A simple way of checking that the water pump is working is to feel that all the cooling system pipes are getting hot proving that the water is being circulated If a noise is present then removal of the pump for examination is recommended A noise from the water pump can be caused by a worn bearing, which carries the tension of the fan belt, when the bearing becomes noisy it usually leads to a leak of coolant from a hole at the bottom of the pump -8Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Hoses Water leak while under pressure Hose leak when under pressure This hose is leaking because of a split near the hose clip Hoses in the cooling system can weaken over time and the operating pressure of the system can cause the hoses to burst emptying the system of coolant, leading to damage if the vehicle is not brought to rest quickly Wear and age can cause splits or cracks Hoses may come into contact with a moving part or chafe through on a sharp edge of the engine or body During servicing it is important that all the hoses are checked and any damaged ones replaced Note: When it is necessary to replace one hose it is normally advisable to replace all of them, if the problem is due to age and general deterioration Hoses may split internally therefore restricting the flow of coolant Air lock The cooling system may have an air lock, this is usually caused by a complete change of coolant e.g when the system has been drained for repairs Most vehicles have bleed screws, which may be found on the coolant pipes The interior heater usually becomes inefficient, even when it is full on, it does not get hot enough to warm the vehicle If the heater is not getting hot then it’s a sure sign that there may be an air lock in the cooling system Cylinder head gasket A leaking cylinder head gasket can also cause overheating, the fault may be linked to white smoke from the exhaust (steam caused by water entering the combustion chamber) or excessive water dripping from the exhaust system The engine may misfire and lose water from the cooling system due to an increase in pressure in the cooling system caused by combustion gases Note: Incorrect ignition timing can cause overheating -9Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Draining and refilling the cooling system Use cloth and remove slowly Turn slowly anticlockwise When draining the cooling system it is important that the radiator and cylinder block are both emptied of coolant Safety first: Pressure is built up within the cooling system when it is hot, the radiator cap must be released slowly to prevent scalding It is therefore wise to let the cooling system cool before draining, if this is not possible then release the radiator cap slowly, covered with a cloth Radiator drain plug Cylinder block drain plug Place drain trays under the radiator and cylinder block drain plugs, remove the drain plugs and let the coolant drain out It may be necessary to remove the drain plugs altogether if they have become blocked -19Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Flushing the cooling system Water flowing from bottom hose and radiator After draining remove the lower hose (bottom radiator hose), insert a water hose into the radiator filler and allow water to flow under pressure, keep the water flowing until the water coming out of the radiator is clear Special flushing fluids may be used to unblock stubborn sediment Just simply follow instructions printed on the container It can also be an advantage to flush the cylinder block at the same time Leaving the drain plug removed and removing any hoses that are fitted low on the engine block can effectively achieve this Note: Remember to leave the heater water valve open (in the hot position) this will cause the water to flow through the heater matrix Reverse flushing of the radiator is best carried out with the radiator removed When flushing is completed, remember to tighten up the drain plugs -20Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Removing and flushing the expansion tank Remove expansion tank for cleaning Remove the expansion tank and filler cap, empty out all old coolant and flush the tank with water, reinstall Refilling the cooling system Fill the expansion tank with the correct mixture of coolant and antifreeze to the correct level Do not over fill Check that the coolant mixture is to the manufacturers’ recommendations Fill the expansion tank with coolant to the full mark -21Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Bleeding the system Air locks are prevented from forming by removing the heater hose to allow air to bleed out of the system Heater inlet hose Water flowing through pushing out the air To bleed air from the system remove the inlet heater hose from the highest point on the engine, or loosen the bleed screw if fitted Refill the cooling system until it begins to flow from the heater pipe (or bleed screw) Reconnect the heater inlet pipe then continue to fill the radiator with coolant until completely full Run the engine at fast-idle speed for several minutes and then check that the level has not changed, this often occurs when the thermostat opens Finally check for leaks around the radiator and cylinder block drain plug and heater hose connection, also check that the heater system is getting warm Note: Remove any debris from the radiator cooling fins, check as appropriate, fan belt tension and that the viscous fan is free to rotate If an electric fan is fitted check that it switches on when the engine temperature rises -22Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Exercise Testing the thermostat for correct operation Thermostat under test Method • drain off the cooling system • remove the thermostat from its housing • place the thermostat and a thermometer in a container of water • heat the water and watch for the thermostat opening • note the temperature at which the thermostat opens • compare the opening temperature with the temperature marked on the thermostat or refer to the vehicle manufacturers’ specifications Carry out tests on several thermostats and complete the table below: Thermostat Opening No temperature Recommended opening temperature Serviceable? Discuss the results with your tutor -23Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Exercise Carry out a pressure test on a cooling system Pressure testing provides a means of testing the cooling system for leaks at its operating pressure with the engine stationary, providing a safe and, if necessary, prolonged search for any problems • remove the radiator pressure cap and top up the cooling system • attach the pressure tester • pump up the pressure until maximum operating pressure is reached If the pressure begins to fall, check for visible signs of coolant leaks, if there are no visible leaks, remove the spark plugs and check for coolant in the cylinders, which would be caused by a leaking cylinder head gasket To test the pressure cap for serviceability connect to the pressure tester and pump up pressure until the cap releases, note this pressure and check that it compares with the correct operating pressure of the cap Discuss findings with your tutor -24Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Exercise Coolant testing To carry out this test it is necessary to use a hydrometer, which measures the relative density of the coolant i.e the strength of the antifreeze/water mixture • take a sample of the coolant into the hydrometer • read the float level or scale • compare the reading with the percentage chart (supplied with the tester) Calculate the amount of antifreeze to be added to give recommended protection Poor Good Using the hydrometer, carry out further tests on a variety of vehicles Using the percentage chart state the temperature that the cooling system is protected to before it will freeze Complete the table: Model of vehicle Capacity of the cooling system Mixture recommended % Discuss findings with your tutor -25Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Ventilation and Heater Systems The purpose of heating and ventilation in motor vehicles is to provide a comfortable driving environment under various weather conditions and to ensure that windows not frost or mist up Various systems are used and can be classified under the following headings: Equipment Ventilator Function Ventilation only Heater Heating and ventilation Cooler Cooling and dehumidification Air conditioner Heating and ventilation, cooling and dehumidification Types Forced ventilation and natural ventilation type Hot water type, exhaust type and a separate integrated fuel driven type Dashboard type, boot compartment type, and integrated separate type Manual and automatic type Ventilator The necessary ventilation per person is in the region of 25 to 35m³ /h The actual size of the passenger compartment is in the region of 2.0 to 3.5m³ Therefore it is necessary to ensure that fresh air is provided even when the windows are closed This type of system is known as a ventilator and is classified into two categories, natural and forced ventilation type Natural air ventilation Negative pressure Positive pressure In the natural ventilation type the fresh air enters the passenger compartment by utilising the forward movement of the vehicle, the air enters in a place which has positive pressure applied, and leaves by a discharge port where negative pressure is applied -26Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue The air inlet is designed to ensure that snow and rain cannot enter the vehicle, body design plays an essential part with regard to correct functioning of the ventilation system Forced air ventilation Air entry points Air exit points In a forced ventilation system a blower is used (fan), a motor is used to blow air into the passenger compartment, this system is integral with the heater system The intake air is mixed in the heater unit before discharging air into the passenger compartment To ensure good distribution of air various ducts are used at various levels Heater system Radiator Blower switch Engine Mode select switch Fresh air Compartment air Blower Vehicle heater systems can be classified into the following types: • hot water type - this type uses the cooling system as a heat source • exhaust type - this type uses the exhaust as a heat source • combustion type - this type uses the heat of an independent burner • the hot water type (as shown) -27- Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Coolant from the engine water pump is fed through the heater matrix, while the air from the passenger compartment (re-circulated air) or fresh air from outside is forced by the blower through the heater matrix where it is heated, the heated air then enters the passenger compartment Air entering the vehicle, can be mixed by the driver to allow for sensible temperature control The air vents can be controlled either by levers (mechanically) or by electric servomotors operated by push button (electrically/electronically) Heating and ventilation (slider controls) Fresh air inlet Defroster nozzles Windscreen defroster vents Right side vent Heater valve Heat exchanger Foot well vents Control unit Left side vent The fresh air is taken in through the bonnet by a radial fan and heated in the heat exchanger and then ducted to the various vents, which are controlled by flaps in the distribution box The fan can be multi-speed and may be capable of 500³ /h -28Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Rotary control knobs Hot in (from engine) Cool out (to engine) Ergonomically designed rotary controls are much more precise than slider controls Heater fan Rotary control knobs are ergonomically friendly and are much more precise than slider controls for adjusting the temperature (middle knob) and air distribution (right-hand knob) When the fan switch is off, the air inlet is constricted e.g there is no fan support, this prevents any noxious smells entering the passenger compartment Pollen filters are normally fitted The design of the foot-well vents and the rear outlets ensure that the air temperature is more evenly distributed -29Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Detailed operation of the heater system Fresh air recirculation select damper Airflow through the heater is controlled by the air mix damper and mode selection dampers for temperature control and outlet selection The dampers can be electrically or mechanically controlled, in electronic control systems servomotors are used, the driver operates these by push buttons on the heater control panel -30Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Exercise Heater operation Carry out the following instructions on a vehicle heater system: • warm up the engine • operate the blower to bring fresh air into the vehicle • operate the FRESH/CIRC select control to operate the fresh/re-circulated air, select damper to select re-circulate air and fresh air • vary the temperature of the air inside the vehicle by operating the air temperature control valve • alter the flow of air from the foot, bi-level and face mode Achieve the conditions shown below: The following four diagrams show the different paths that the air would flow through the heater system, depending upon switch position on the heater console Notice the varying positions of the dampers Heater mode -31Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Bi-level mode Defroster mode Ventilation mode -32Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Vehicle heating systems - trouble shooting Symptom Engine runs cold heater is cool Possible cause Engine thermostat failed in the open position Remedy Replace Electric fan runs continuously Fit new temperature switch Heat control valve defective Check cable setting and valve opening/closing operation Examine servo motor operation if fitted Bleed the system Air lock in system Heater cool Heater ineffective Engine cold Refer to engine fault chart engine cold Air hoses/channels from fan housing to heat exchanger insecure or damaged Check hoses secure and replace as necessary Heat exchanger flaps – operating arms and/or control cables jammed, broken or disconnected Check the operation of control cables and operating arms and that the arms are moving the flap spindles on the heat exchanger properly -33Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue ... Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Common Faults Associated with Cooling Systems The cooling system of a motor vehicle is designed to dissipate... and general maintenance of the cooling system -16Copyright © Automotive Skills Limited 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Cooling and Heater System Exercise Maintenance Carry... 2003 All Rights Reserved LV21: Cooling Systems (2) Issue Exercise Carry out a pressure test on a cooling system Pressure testing provides a means of testing the cooling system for leaks at its