La construcción de identidad a partir del arraigo con el territorio

1. Why must the exhaust gases not be discharged into the garage?

2. What are the dangers from unguarded fan blades and fan belts?

3. What is likely to happen if the radiator cap is removed quickly when the engine is hot?

Activity

1. (a) Disconnect hoses and housing and remove the thermostat from the engine.

(b) Place the thermostat in the tester and heat the water to the opening temperature of the thermostat, watch for commencement of opening and fully open point, note the temperatures and record the results. Note: It may be necessary to first subject the thermostat to boiling water so that the fully open position can be assessed.

(c) The recommended opening temperatures should be obtained from the data book. (d) Replace the thermostat in the correct posi-

tion, refit the housing using a new gasket as required, fit hoses and tighten hose clips, run engine and check for water leaks.

2. (a) Remove radiator cap. (Observe safety instructions.)

(b) Fit pressure testing equipment in place of the radiator cap, operate pump to pressur- ize system to recommended pressure. (c) Carry out visual inspection of components

in the cooling system and joints for coolant leakage.

Note: Look for a steady reading of the pressure tester gauge; if the pressure falls steadily and there is no coolant leakage then an internal leakage of the coolant can be suspected. (Check that the tester unit is fully sealed on the radiator neck.)

(d) To identify internal leakage there are pro- ducts on the market which can be mixed with the coolant, the system is closed and the engine is run until it reaches its normal operating temperature. After the system cools the radiator cap is removed and the colour of the coolant is inspected. The che- mical changes colour when it comes into contact with oxygen. Therefore if the colour of the coolant changes it can be assumed that air is entering the system, most probably through the cylinder head gasket.

(e) The radiator cap can be checked for cor- rect operation by fitting the correct adap- tor to the pump and fitting the cap in place on the tester. The pressure is then raised by operating the pump and recorded when the stage is reached for the seal and the spring in the cap to lift and so relieve the pressure.

3. To flow test the radiator.

(a) Remove the radiator and fit it to the test rig. (b) Fill the header tank of the rig with a known

quantity of water.

(c) Open the tap to discharge the water through the radiator and measure the draining time with a stop watch. Compare this with the manufacturing data (20 litres takes approximately 20 seconds for a car radiator with a water head of 0.7 metres). (d) The mineral deposits in the coolant tend to

block the water ways, so an approximation of the flow rate can be ascertained by com- paring the mass of the radiator under test with the mass of a new radiator of the same type. The deposits are heavy so a 25% increase in weight will give an indication of several mineral deposits.

Questions

1. What are the effects of pressurizing the cooling system?

2. Explain the function of the two valves in the pressure cap.

3. List five reasons for an engine becoming over- heated.

Self assessment questions

1. A thermostat is fitted to cooling systems: (a) to provide a variable current in the tem-

perature gauge circuit

(b) to control circulation of coolant to help the system to warm up quickly and to maintain a constant operating temperature

(c) to act as a control to switch the cooling fan on and off

(d) to operate the compressor on an air con- ditioning system.

2. The lubrication system of a certain engine con- tains 0.8 kg of oil that has a specific heat capacity of 1.7 kJ/kgC. During the warm-up period the temperature of the oil rises by 30
C. The amount of energy transferred to the oil during this warm up period is:

(a) 32.5 J (b) 325 MJ (c) 40.8 kJ (d) 408 J

3. Inside a pressurised cooling system:

(a) the coolant boiling temperature is above 100
C

(b) the increased pressure slows down the cir- culation of coolant

(c) the boiling point of the coolant is lowered (d) the convection currents cease to operate 4. Ethylene glycol based anti freeze when added to

the coolant causes:

(a) less evaporation of the coolant

(b) the freezing temperature of the coolant to be raised

(c) the freezing temperature of the coolant to be lowered

(d) the boiling point temperature of the cool- ant to be lowered

5. The purpose of the water pump in a cooling system is to:

(a) pressurise the cooling system (b) circulate the coolant

(c) eliminate the need for a radiator (d) reduce heat loss

6. After combustion the temperature inside the engine cylinder is:

(a) approximately 200
C (b) approximately 12 000
C

(c) approximately 1400
C to 2000
C (d) 250
C

7. Cooling systems rely on heat transfer by: (a) pressure differentiation

(b) electrical conductivity

(c) Archimedes principle

(d) conduction, convection and radiation 8. Radiator surfaces are often finished in matt

black because:

(a) this surface is effective against corrosion (b) this surface is most effective in radiating heat (c) this type of finish reflects most heat (d) this surface finish prevents heat escaping

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