Mechanics > Cooling System > Flashcards

Cooling System Flashcards

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1
Q

What is the purpose of the cooling system?

A

Get engine up to operating temp as quickly as possible
At required temperature for efficient combustion to take place and maintain it at that temperature

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2
Q

What is the ancillary function of the cooling system?

A

Proving heat for the passenger compartment

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3
Q

What are the types of cooling system?

A

Air-cooled

Water-cooled

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4
Q

Why is the Diesel engine more efficient?*

A
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5
Q

What % of thermal energy is converted into power?

A

23%-28%

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6
Q

Where do petrol engines lose efficiency?

A

Exhaust gas loss
Cooling loss
Pumping loss
Friction loss

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7
Q

What are the 3 ways heat can be transferred?

A

Conduction
Convection
Radiation

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8
Q

What type of cooling do cooling fins do?

A

They cool by convection

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9
Q

What are the advantages of air cooling?

A

Free

Lighter

Doesn’t leak = less maintenance

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10
Q

What are the disadvantages of air cooling?

A

Fit a large fan for warm days

Noisier

Hot spots (areas that do not cool because debris is trapped in fins)

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11
Q

What is the advantage of water cooling?

A

Quicker at warming the engine up

Quieter

More efficient = no hot spots

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12
Q

What is the disadvantage of water cooling?

A

Can leak and freeze = high maintenance

Heavy

Expensive

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13
Q

How does a basic water cooled system work?

A

Circulating coolant around the engine aborbs heat energy form cylinder by CONDUCTION

Excess heat is transferred to the air using the radiator

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14
Q

What operating temperature does the water cooled system keep the engine at?

A

Between 90-105C

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15
Q

Why is a fan needed?

A

To ensure there is always sufficient air flow through the radiator

Needed when no longer moving

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16
Q

What is the role of core plugs?

A

Seal the coolant jacket holes left by the manufacturing process

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17
Q

What is the deck surface and why is it ground flat?

A

It is the the top of the engine block

It is ground flat to ensure the cylinder head makes good contact

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18
Q

What are cylinder sleeves/liners typically made of?

A

Cast iron or steel

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19
Q

Describe dry cylinder sleeves

A

Dry sleeves are thin and supported by the engine block material

Uses conduction to transfer heat

They are not in direct contact with the coolant and are generally pressured into the block

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20
Q

Describe wet cylinder sleeves

A

Coolant is in direct contact with wet sleeve = improving cooling efficiency

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21
Q

What is fitted at the top and bottom of wet cylinder sleeves?

A

A seal is fitted at the top and bottom of a wet sleeve to prevent coolant leakage into the oilways or pressurizing the cooling system

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22
Q

What is the difference between dry and wet cylinder sleeves?

A

Wet sleeves are thicker than dry sleeves because there are no structure support from the engine block

Wet sleeves have the seal fitted at the top and bottom to prevent coolant leakage into oilways or pressurizing the cooling system

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23
Q

What are the basic parts of the water-based cooling system?

A

Water jacket

Water pump

Hoses

Radiator

Radiator cap

Thermostat

Cooling fan (fixed/electrical)

Heater

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24
Q

Before using water pumps, what system was used that relied on convection?

A

Thermo-siphon system of cooling

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25
What is the purpose of the radiator?
Cool the coolant after is becomes hot from going through the water jackets
26
Where is the radiator located?
Front end of the vehicle, so the wind created fro the moving vehicle can also help cool it
27
What components are found in the radiator?
Radiator cap Hoses Radiator core = between tanks Outlet Drain cock
28
How does the radiator work?
Coolant enters upper tank from upper hose Coolant moves into radiator core, many tubes which help cool the fluid as it makes it way down into the lower tank Radiator core also contains many exposed cooling fins = that removes heat from coolant
29
What is found in front of the radiator?
A/C condenser
30
What is needed in the core tubes of the radiator?
Turbulance, to cause the hot water to mix with the cool water
31
How did radiator blinds operate and why are they no longer used?
Spring-loaded roller blind prevents too much cooling Cable controls enables blind to be raised to black off as much of the radiator as necessary Temp gauge is fitted to regulate the temp of cooling water Used to seize so is no longer used
32
How did radiator shutters operate and what are their advantages?
Metal strips blank off the airflow through the radiator By turning 90 degrees a free passage for air is provided Help with air resistance to improve on efficiency and lower emission produced
33
How did active griller roller covers operate and what are their advantages?
The system consists of a roller cover with 5 plates that can regulate the opening to the radiator in a number of step from fully open to fully closed Better version of radiator shutters, also reduce wind resistance and can lead to faster warming of the engine
34
What temp does wax pellet thermostat open at?
85-95 degree Celsius
35
Explain the steps a wax pellet thoermostat goes thorugh from cold to hot engine
Cold engine = wax pellet is solid, spring valve keeps valve closed = preventing coolant from going to radiator (coolant ciruclates within the engine) Warm engine = wax turns to liquid and expands, pushing needle up and forcing open valve against spring pressure Coolant can now flow from teh engine to radiator to be cooled
36
What material is the fuel tank made of and why?
Plastic = weight reduction and no corrosion
37
What two things are needed for a fuel tank to work?
Gap at top of fuel tank for hydrocarbon vapour to sit Air breather so vacuum is not created
38
Where is a charcoal canister found and what is its purpose?
On the fuel tank = good filtration device to absorb hydrocarbons Modern cars have evaporation (EVAP) system = slightly pressurized to prevent dust/dirt entering
39
What do evapouration systems do?
EVAP)system = slightly pressurized to prevent dust/dirt entering
40
What was the issue with the mecahnical fuel pump?
Was operated by the cam shaft, which pushed the rred valves allowing fuel to circulate Issue was that when engine wasn't moving, no fuel was circulating Also diaphragm could split
41
What is the electric fuel pump called?
Roller cell fuel pump
42
How does the electric fuel pump operate?
Driven by a permanently magnetic electric motor, to spin an OFFSET rotor disc As rotor spins, centrifugal force presses the rollers against outer ring This traps and moves fuel thorugh pump's chamber to create pressure at the output and suction at the input
43
What valaves are found in the electirc fuel pump?
A safety valve will connect the pressure and suction ends when there is an abnormal increase in pressure A check valve in the pressure connection provides the necessary supply pressure for when the engine is restarted from hot The valve will close when the engine is turned off
44
What is the purpose of the radiator cap?
Seal the readiator tightly, keeping the pressure All coolant temperature to exceed 100C without boiling
45
Why is the radiator cap needed?
Pressure can increases the temp difference Also makes it possible to reduce the size of the radiator without interfering with its ability to cool the engine
46
In a sealed system what is the relationship between pressure and boiling point?
Increasing pressure on liquid or vapour increases the boiling point and vice versa Example Radiator cap allows the pressure in the engine cooling system to reach 1.1 bar, raising the boiling point of the coolant to 127C
47
How does a radiator cap work when the temp rises?
Pressure cap has a built-in relief valve and a vacuum valve When the temperature rises, coolant expands. The expanded coolant creates more pressure . At a predetermined pressure the relief valve opens.Excess pressure escapes through the overflow pipe
48
How does a radiator cap work when the temp drops?
Pressure cap has a built-in relief valve and a vacuum valve When the engine stops, the coolant temperature drops. A partial vacuum forms inside the radiator. Vacuum valve opens automatically, this draws in fresh air which fills the vacuum inside the radiator When the engine is cold, the coolant is at atmospheric pressure .
49
What is the purpose of the coolant reservoir tank?
To prevent coolant loss Elminate the need to replenish the coolant constantly
50
Where is the coolant reservoir tank located?
Connected to the radiator by the overflow hose
51
How does the coolant reservoir tank work?
When the rising engine temperature causes the coolant to expand, the excess coolant flows into the reservoir tank When engine temperature drops, coolant returns to the radiator
52
Why is it important rubber hoses are flexible?
To allow for engine vibrations without damaging components
53
Where do the upper and lower coolant hoses carry coolant to and from?
Upper = from cylinder head to radiator Lower = from radiator back to water pump
54
Where do the smaller hoses carry hot coolant to?
Heater matrix
55
What can be fitted to prevent hoses from collapsing under low pressure when engine is cold?
Support spring
56
Where may a support spring be needed and why?
Radiator hose to prevent collapse under low pressure when the engine is cold
57
Name 3 types of fan
Fixed fan Temperature controlled fan (viscous fan) Electric motor driven fan
58
How does a fixed fan work?
This fan is driven constantly by the belt The fan speed changes in proportion to the engine speed
59
How does a temperature controlled fan work?
Bi-metallic spring, when headed will bend because one metal will expand faster than the other This spring is in a coil, so when too hot = expands and locks the fan on
60
How does a electric motor driven fan work?
Uses a thermistor to turn the electric motor circuit on/off
61
How does a thermistor work?
When cold = has high resistnace so no current can pass
62
What is the typical composition of coolant?
50/50 mixture of water and ethylene glycol (antifreeze) Corrosion inhibitors
63
What are the roles of coolant?
Lubricates the water pump Prevents rust and corrostion Helps transfer heat from engine to radiator and heater matrix (in passenger compartment) Lowers freezing point of waterin the cooling system Raises boiling point of the coolant
64
What type of coolant is light blue/green?
Inorganic acid technology Typically used in older vehicles
65
What type of coolant is red/orange?
Organic acid technology Commonly used in modern vehicles
66
What type of coolant is yellow/gold?
Hybrid organic acid technology
67
What type of coolant is pink/purple?
Phosphated organic acid technology
68
What type of coolant is dark blue?
Silicated organic acid techology
69
Why was waterless coolant invented?
To circumvent the problems of vapourizing water When water vapourises it retians only 4% of its thermal conductivity
70
What are the benefits of waterless coolant?
Environmentally beneficial = reduces the use of cooling fans and therefore improves fuel economy Also it doesn't generally need chaning = reducing hazardous waste following repeated coolant flushes
71
What tests can be done to measure antifreeze strength?
Using a hydrometer or refractometer
72
How does a hydrometer measure antifreeze strength?
Measures water content in brake fluid Has to be compared under the same temperature
73
How does a refractometer measure antifreeze strength?
Thicker liquid will cause the light to bend more
74
Why is a pressure tester needed and what does it do?
Allows you to check leaks in a coolant system at a cold temperature By simulating the pressure of a hot system Some leaks only occur if hot/cold because different materials expand and contract at different rates under different temps
75
What are the reasons for a head gasket failure?
Compression leaks to crankcase smoking & blow by Compression leak to coolant overheating Blown to coolant port water in oil Compression leaks between cylinders misfire or rough idle Blown to outside oil leak Blown to outside coolant leak
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