The proportion of ethylene-glycol-based anti- freeze present in a cooling system can be deter- mined by checking the specific gravity of the coolant and by reference to its temperature. The percentage of anti-freeze is measured by the use of a hydrometer and a thermometer.
The graph in Fig. 2.26 shows what happens to water when an anti-freeze solution is added. The water changes from a liquid to a mush before becoming solid ice. This ability to form mush before becoming ice gives some warning of freezing and consequently of the danger of damage to the engine.
Methanol-based anti-freeze is also used but has the disadvantage of losing its anti-freeze effect due to evaporation. It is also inflammable. Both types are toxic, and if spilt on the paint work of the vehicle would damage it.
Figure 2.27 shows how to check the anti- freeze content using the ‘Bluecol’ hydrometer. The coolant is drawn into the hydrometer to a level between the two lines. Note the letter on
the float at the water line and the temperature of the coolant on the thermometer. Using the slide rule, line up the two readings of temperature and letter. The true percentage content of anti- freeze can be identified at the ‘read off’ point.
Faults and their possible courses are shown in Table 2.1.
2.15 Engine temperature
gauge
The engine temperature gauge permits the dri- ver to observe engine operating temperature. In
the temperature indicator circuit shown
in Fig. 2.28 the main features are the thermal
Fig. 2.25 Build-up of deposits in the cooling system
Fig. 2.26 Variation of freezing range with different strengths of anti-freeze
type gauge, the negative temperature coefficient sensor (thermistor), the voltage stabiliser and the interconnecting circuit.
The sensor is normally situated in the cylinder head of the engine and the sensing element is surrounded by coolant. In a typical cooling sys- tem sensor, the resistance of the sensing element varies from approximately 230 ohms at 50C to approximately 20 ohms at 110C. This variation of resistance causes the current flowing through the bi-metallic element of the gauge to vary. The variation of current causes the temperature of the bi-metallic element to change. The change of tem- perature causes the bi-metallic element to bend and so causes the gauge pointer to move to indi- cate coolant temperature. Because the operation of the gauge is dependent on a steady voltage being applied, the circuit includes a vibrating con- tact voltage stabiliser which also relies on a bi- metallic strip for its operation.
Learning tasks
1. Explain in your own words what is meant by semi-conductor.
2. How should the temperature sensor/transmit- ter be checked for correct operation? Name any special equipment that might be required. 3. Remove a temperature sensor and test for electrical resistance, both when cold and when hot, note the readings and check your results with the manufacturer’s data. Make recommendations on serviceability.
4. Where in the cooling system would a tem- perature sensor be located? Why would it be fitted in this position?
Fig. 2.27 (a) ‘Bluecol’ hydrometer, (b) slide rule for use with it
Table 2.1 Liquid cooling systems fault chart
Fault Possible cause
External leakage
1. Loose hose clips or split rubber hose 2. Damaged radiator (cracked joints
or corroded core)
3. Water pump leaking (bearing worn) 4. Corroded core plugs
5. Damaged gaskets
6. Interior heater, hoses, valves 7. Temperature sensor connection
leaking Internal
leakage
1. Defective cylinder head gasket 2. Cylinder head not correctly tightened 3. Cracked water jacket internal wall 4. Defective cylinder liner seals
Water loss 1. Boiling
2. Leaks – internal and external 3. Restriction in radiator
4. Airways in radiator matrix blocked Dirty coolant
(corrosion)
1. Excessive impurity in coolant water 2. Infrequent draining and flushing of
system (where required) 3. Incorrect anti-freeze mixtures 4. Lack of inhibitor
Over-heating 1. Loose, broken, worn or incorrect fan
belt tension 2. Defective thermostat
3. Water pump impeller loose on shaft 4. Restricted circulation – through
radiator, hoses, etc. 5. Radiator airways choked 6. Incorrect ignition timing 7. Incorrect valve timing 8. Tight engine 9. Low oil level
10. Insufficient coolant in system
Over-cooling 1. Defective thermostat
2. Temperature gauge incorrect 3. Electric fan operating continuously
2.16 Engine core plugs
These are fitted for the following reasons:
.
they may blank off the holes left by the jacket cores during casting or machining;.
they may be removed for cleaning out corro- sive deposits from the jacket.The plugs may be of the welsh plug, drawn steel cup or, less commonly, the screwed plug type. The first two are expanded and pressed into core holes that have been machined to size. All three are shown in Fig. 2.29.
2.17 Heating and
ventilation
The most common method of providing a comfortable atmosphere in the car is through
the heating and ventilation system. In some countries it could mean that a full air- conditioning unit is required where refrigeration cooling is fitted to the vehicle. Fresh air ventilation comes under two headings, direct and indirect, the heat source being the hot water from the engine. But it may also be gained from a number of other sources such as the exhaust system, as in the air-cooled engine, or in a sepa- rate heater where fuel is burnt to heat a chamber over which air is passed, or electrically, in which an element is heated and air passed over the element. The water type are normally fitted to the bulkhead or behind the facia panels and are the most common arrangement in light vehicles.