Head-Mechanics

The cooling system of a car consist of:

Water
Antifreeze
Thermostat
Cooling jacket
Water pump
Radiator and radiator cap
Expansion tank
Cooling fan
Pipes to connect it all.

WATER
Engines can be either air-cooled or water-cooled. Most engines are water cooled because for the same volume of water and air water can carry up to ten times more heat away than air can.

ANTIFREEZE
Antifreeze is used to impurity the water. Impure water has a higher boiling point so by adding antifreeze it raises the boiling point slightly. Its other purpose is to slow down the process of electrolysis. Some current will flow through most cooling systems due to the fact a car is very hard to earth, the cooling system is kept insulated but as time goes by this isolation breaks down and current will flow through the water by adding antifreeze you can reduce the waters conductivity slowing down the process. If not a badly insulated cooling system with just water can rot the system in a matter of 20,000 miles.

THERMOSTAT
The thermostat is used to control the temperature of the coolant around the engine. As the engine warms up from a cold start the thermostat will stay closed keeping the cold coolant in the engine. As the temperature of the coolant increases the thermostat will open allowing the flow of coolant to the radiator. The purpose of this is to allow the engine to warm up quickly. If the engine is too cool oil will remain to thick and not lubricate the engine. Another reason to warm the coolant up quicker is that the engines automatic choke is run from the coolant temperature sensor. If the coolant never warms up the choke will remain on and use more fuel. However if the engine is run to hot the oil will be to thin and again will not lubricate the engine. As the water gets hotter it expands and will cause the pressure in the system to increase and possible damage to radiators and pipes will occur. If the temperature gets to high the aluminium head can become twisted or warped breaking the seal between the head gasket and block/crankcase, this result is known as head gasket failure.

COOLING JACKET
The cooling jacket surrounds the combustion chamber. The cooling system works by conduction, convection, and radiation. The cooling jacket is the first step in the three-stage process. Conduction is the flow of heat from a hot substance to a cool substance. The large surface area of the cooling jacket allows for a good flow of heat to the coolant. The cooling jacket is then the ability to take the heat from the combustion chamber via coolant to the radiator.

WATER PUMP
The water pump is how the engine moves the flow of water quickly from the engine to the radiator. The water pump is connected to the engine via a belt or pulley. In this way as the engine spins faster with demand the water pump increases at the same rate to the engine. Allowing the cooling ability at all engine spends.

RADIATOR
The radiator is second and third step in the conduction, convection, and radiation. The hot water flows through the radiator through veins. These veins are covered with smaller veins. These smaller veins increase the surface area of the radiator. The surface area can be as much as a small football field. These veins allow the hot water to be cooled by the movement of air through the veins. This is the process of radiation. The process of convection is that cooler water is denser that hot water which rises so the flow of water can be seen when the hot water is cooled. This difference is why the top radiator hose is hot and the bottom cool. The bottom pipe is fed into the engine were as the top is fed out of the engine.

RADIATOR CAP
The radiator cap is a way of controlling the pressure in the cooling system. The pressure of the cooling system is around 15psi or 1 atmosphere. This increase in pressure increases the boiling point of the coolant allowing the coolant to run at a lower temperature and stopping the boiling process of the water. If the pressure in the system were to escape the boiling point of the water would fall from 118oc to 100oc. This would allow the water to boil at some of the engines hot spots like around the exhaust ports/valves. When the water boils it incorporates air into the system and greatly reduces the cooling process and can burn out the valves if they get hot enough. This localised boiling however will not be recorded on the coolant temperature gauge on the dash. It pays to have the cap pressure tested every year or replaced. A faulty cap may be spotted when a hot engine is tuned off. As the temperature rises slightly, and hence the pressure in the coolant system, strange gurgling noises may be heard in the vicinity of the cap as the steam and hot air escapes. It may not always be the radiator cap other leaks will cause the same problem.

EXPANSION TANK
The expansion tank allows thr radiator to be filled to the top without bursting the system. As the water heats up it expands if the radiator was filled and sealed when cold it would burst when it got hot. The expansion tank allows the water to rise and fall whilst keeping the pressure.

COOLING FAN
The fan allows the flow of air through the radiator when the car isn’t moving. If the car were to stay stationery it would eventually overheat. The fans are controlled via a relay and a temperature sensitive switch located in the radiator. The fans come on automatically when the switch senses the temperature rise to around 85oc.

PIPES
Pipes are used to connect the system together. Usually rubber pipes are used which allow them to move with the vibration of the engine. If all metal pipes were used they would crack rather quickly. The other advantage of rubber hose over metal is rubber doesn’t corrode in water like steel.
 

Your MGF should not smoke excessively from the exhaust:
LIKE THIS

We can fix it.