Cooling

Direct Cooling

Direct cooling is done by using the fresh or salt water brought in by the seacock which is pumped up to the engine then pumped through and around the engine until it is discharged out the exhaust. This system will require a water or circulation pump and a water strainer, some engines have trouble with this system as most engines use radiator coolant in a closed loop system which means the cool water running through the heads can be to cold  for the engines running temperature.

Indirect Cooling

What is the purpose of a heat exchanger and how does it work?

The purpose of the heat exchanger is to keep the water cool and create a transfer of heat from one liquid to another through a solid surface. It uses hot engine coolant which is past closely to cool raw water in plates or through pipes. The heat is transferd from the cool water to the hot coolant and vice ceversa so that the engine coolant temperature drops and the cool waters temperature rises before it is discharged out the exhaust.

What is the core of the heat exchanger made of?

The heat exchanger core can be made from a number of metals but they are mostly made from alluminum, copper and stainless steel which is the least expensive compared to heat exchangers that use nickel, titanium cupronickel.

What is the purpose of a thermostate?

The purpose of the thermostat in engines is to stop the coolant flowing through the cylinder block and engine untill the engine has reached its operating temperature . The thermostat is mounted on the side of the engine block which is normally at the top of the radiator hose inlet and as the temperature rises to its set temperature the thermostat opens up which allows the coolant to flow throughout the system untill it drops below the temperature then the thermostat will close again. 

Radiator Pressure cap?

The radiator pressure cap is mounted on the top of the radiator where the radiator is filled, the pressure cap opens up a specified pressure where it lets the pressure out and directs the fluid out into the overflow bottle or on to the ground. For different vehicles the caps will have different pressure ratings if you have a faulty pressure cap it could cause overheating and engine damage from getting to hot. It uses a spring which opens up when the cooling system has reached a certain temperature and pressure to lower the boiling point.

Why and what is the purpose of a core plug

The reason why we have core plugs on engines is for manufacturing purposes when the block is being cast and it is put in to remove all the sand and debri from the block once it has been cast. They are small plug holes in the side of the engine block and are also there for cold climates where the coolant freezes and expands which will pop out a core plug instead of cracking the cylinder block.

How does the centrifugal circulating water pump work?

Centrifugal pumps have a housing with rotor type impellor's which spin on a shaft and makes the water passing it speed up and increase the flow of water which will be pumped through the system until it comes back to the pump. This pump converts the mechanical energy from the moving impellor to increase the overall pressure of the coolant.

Why is it important to lubicate the impellor when fitting from new?

When fitting a new impellor you must lubricate the housing and impellor with marine grease of some kind of lubricant or it will run dry and can cause more wear and stiffen operation.

When fitting a impellor what should you check before refitting the housing and why?

When fitting a impellor you must check that the impellor fits without play and the that the housing and gasket go in place evenly.

What is the purpose of a oil cooler and how does it work?

The oil cooler is put in place to remove the hot oil from the engine and run it through  the oil cooler which has fins that cools the oil down then it is replaced back into the engine this helps to keep the engine cool and to raise the boiling temperture of the oil.


What is the process of a intercooler/aftercooler how does it work?
The intercooler is put in place to cool the air and increase the density of the air flowing through it as it is forced through the fins of the intercooler as air is passing around it which cools the air  and makes it more dense .

Why do we have Inhibitors & antifreeze?

Antifreeze is used to lower the freezing point of the coolant so the engine doesnt freeze up and crack the block and it can raise the boiling point of the coolant . And it helps to stop corrosion and flaking in the system. Different climates and engines will use different grades of antifreeze

How do you test Antifreeze?

By buying a antifreeze tester and waiting at least 15minutes till your engine has cooled down enough to work with. Then with your antifreeze tester you suck up the coolant in your radiator which will make certain floats inside the tester rise then depending on how many balls rise inside the tester will tell you what percentage of the coolant is antifreeze. Different climates and engines will require different percentages.

What is cavitation corrosion?

Cavitation corrosion is caused by a liquid fluid running past metal or rubber components and create cracks and splits on the surface of the material it is said to be caused by an implosion of gas bubbles onto a metal surface.

What is galvanic corrosion?

Galvanic corrosion is caused by two electrical components that are touching to corrode into eachother it is a electro-chemical reaction.

Stray corrosion?

This is called stray curent corrosion as it is created from the battery and alternator charging system not having a good enough ground and the voltage tracks through the radiator and system causing a electrolytic corrosion.

Stress corrosion?

Stress corrosion is also known as SCC (stress cracking corrosion) which affects most of the metals by cracking under high pressures, temperatures and exposures which cause the metal to crack. Some SCC look bright and shiny but when you look close there are microscopic cracks which go undected.



Crevice corrosion?

Crevice corrosion is caused by small gaps and crevices where water or fluid collect and cant run off which causes corrosion to start and build up between the two surfaces.

What is Electrolysis?

Electrolysis is a corrosion which affects electrical components which decomposes the metal and corrodes connected components

Why and what is bonding in the marine industry?



Bonding is when you connect all the components that are metal to a common earth strap for corrosion devices and will remove the stray current from electrical components and so there is a secure earth for all components.

What are sacrifical anode made off?

Anodes are made from zinc and are mounted in the stern drive or outboard on metal components which it draws the salt and helps protect the boat from corrosion.



Who invented the diesel engine and when?

A guy named Dr Rudolf Diesel who was a mechanical engineer which invented the diesel engine in the 1897. He moved on to creating other systems along side and to work with the diesel engine.

What fuel pressure would you get from a diesel lines?

From the normal diesel engine the pressure is much lower as it uses an injector pump which pumps out at about 150bar and on a common rail diesel engine it is much higher and only trained technicians can work on these fuel lines as the can put out at least 1000bar/1500psi but pressures can be much higher the third generation of common rail can reach up 26,000psi which could easily cut off your hand.

How does the diesel pump work and why do we need to time the pump?

There is two types of diesel injection pump there is a rotor type and an inline type. The rotor design has a hollow cylinder with ports and a cam which is supplied fuel to as it turns , as it spins it opens the ports directing the fuel into the cylinder's. The more commonly used inline system has a cylinder for each in the combustion chamber and uses a piston which moves in sequence with the piston in the engine and each time it pumps fuel up to the injectors to be sprayed. Because the fuel must be sparyed into the cylinder at the right time to ignite the fuel if the timing is wrong the engine will run rough and puff out smoke or not run at all.

How do you time the pump and with what equipment would you use?

First you will start by puting your engine to TDC then you will remove the cambelt then look and line all of the timing marks up including the diesel pump. Then you will put the cambelt on without moving the marks. Tighten up the belt then screw a D.T.I gauge in the back off the diesel pump. Then in the manufactures specs it will tell u to set the engine 3degrees before top dead centre then turn the engine at look at the gauge and it will tell you a reading which you will check in the specifications. You will need a timing light to check if everything is in proper order, you will also need a D.T.I gauge that has a fitting to go in the back of the pump, you will need a socket set spanners and a big screw driver or bar.

How does the diesel injectors work?

The diesel injector is bigger then a normal injector and has diesel feed to it from the top it also has a pump which pumps air into the injector which highly pressurizes the fuel then the needle valve opens spraying the  atomized fuel out the nozzle which has many holes in it which sprays the mixture throughout the combustion chamber which ignites in the pressurized cylinder.

Why do you need to bleed a diesel engine after replacing a fuel filter or removing the pump?


When removing the filter or pump you automaticly will be letting air into the system which will affect the running of the engine because instead of having diesel there will be just air which may cause a air lock. You must full the filter cup up after then bleed the system  to remove the left over air


How do you bleed the system?

 

Once you have changed your new filter you should fill the filter cup with clean diesel then screw together. Then you open the bleed screw on the side of the hand primer and pump it till you see there are no bubbles or air with the fuel Then you should crank the engine and see if its running good but if not you must bleed the injector pipes. You crack the bolt then crank the engine which will make fuel spray out , once there is no bubbles tighten the pipe and carry on bleeding each injector pipe one at a time.

How does a turbo work?

 A turbocharger is a component which is mounted on the exhaust manifold which is designed to force air into the combustion chamber to increase engine torque or power it does this by using the exhaust gases passing by it to spin a propellor and shaft which spins the opposite side of the turbo which has another propellor which sucks in air from the air intake and forces it into the throttle body

What is the knock sensor for and where is it situated?

The knock sensor is a sensor that is put in to detect knock or pinking in the engine it has thing called a piezo crystal inside it that as it is hit or knocked it sends out a voltage to the ECU which retards or advances the timing to stop the knock it is mounted on the side of the cylinder block.

What is the purpose of a glow plugs and how do you test the circuit?

 

The glow plugs are put in place to pre-heat the combustion chamber before the diesel engine is started if it has no glow plugs it wont start or will take a lot of time to heat the cylinders. You would test the resistance in each of the glow plugs if it doesn’t show a reading then its defective and if it does show a reading then check the specifications for these plugs.

Why do we need a turbo fitted to a diesel engine?

 With any internal combustion engine if more air or fuel is added it will produce more power and diesels normally run at low rpms which means they cant really suck in as much air as they need so that is why a turbo is fitted so give more air at certain rpm ranges.

What is a supercharger?

A supercharger is another component which uses forced induction to increase engine power and torque this is a belt driven component which as the belt is spun it  which spins impellors inside the supercharger which sucks in air from the atmosphere and pushes itaround the impeelors and pushes it out into the throttle body. The disadvantage of the supercharger is it uses alot of engine power to run so if the engine is putting out 350 horsepower the supercharger will be using 50 horsepower to run so theonly 300 horsepower can be supplied to the wheels.

Whats the difference between a turbo and supercharger?

The difference between the turbo and supercharger is that the turbo uses the exhaust gases passing it to run and suck in air while the supercharger uses engine power to produce the forced induction. The turbo is more effecient because it uses wasted energy to run rather then engine power.

Why do we need a after- cooler or inter-cooler fitted to a diesel engine?

 An intercooler is designed like a radiator it has fins which air passes through to cool the air which is flowing through the intercooler. The reason an intercooler is put in is to cool the air before it is forced into the throttle body so the air is less dense. If the air is to hot it could cause engine damage by pre-ignition or detonation.

What is the electronic fuel shut off valve used for?

The electronic fuel shut off valve is used to shut off all fuel going into the engine incase of an emergency or if the ignition is turned off which automatically shuts the engine off. It is controlled by a solenoid which as power is supplied to it , it creates a magnetic field which opens or shuts a valve which is supplying the fuel.

What is the purpose of the governor?

The governor is put in place to keep the engine below a certain rev range and because diesel engines are not self speed limiting the govenor is put in to give engine feedback to know when to change the engine speed and to keep it at a constant speed once reached there are many types of governors for different purposes

Electronics



ECU- Electronic control unit

The ECU is the brain of the modern engine which uses lots of sensors to know what the engine is doing at all times and its job is to read this information and make the correct changes to the engine. The ECU is just a computer with inputs from sensors and actuators to control what is going on. If this component is damaged the car wont run or perform normally.

Mass air flow sensor

The MAF sensor is used to know the mass of air that is entering the intake at all times and tells the ECU through the changing of voltages as air passes it. The ECU then looks at these reading and knows whether to add more or less fuel to the engine. There are two types of MAF sensors one is a vane type which moves a diaphragm inside and the other uses a hot wire to determine the amount of air.

Intake air Temperature sensor(IAT)

The air temperature sensor is inside the intake and measures the heat of the air that’s that’s passing it. As it heats the resistance drops which tells the ECU which makes changes to the air/fuel mixture when needing to.

TPS throttle position sensor

The throttle position sensor is on one side of the throttle butterfly and changes its voltage as the throttle moves so that the ECU knows where the throttle is at, at all times so it can make changes to the engine.

Throttle body?

The throttle body is the part of the intake that controls how much air is going into the intake manifold at all times. It has a throttle butterfly inside it and as it turns it opens and close the butterfly. This is the main mechanical control on the engine and is mounted on the end of the intake manifold or on the carburetor.

Engine Coolant temperature (ECT)

 

This sensor is mounted on the by the thermostat which it reads the temperature of the coolant and tells the ECU by changes its resistance so then it can make changes to the engine performance.

 

Fuel rail

A fuel rail is a rail which constantly has fuel at pressure in it to supply to the injectors which come off the fuel rail and need a constant pressure. Some fuel rails have fuel pressure regulators to control the fuel pressure. It has an inlet and most of the time a return to the fuel tank for any left over fuel.

Fuel pressure regulator

A fuel pressure regulator is put in before and sometimes after the fuel rail which controls the pressure at a constant rate that is above the intake manifold pressure. These come in all shapes and sizes and you can get aftermarket regulators that can be adjusted if u need more or less fuel.

Injectors

The injectors are positioned between the fuel rail and the cylinder head on the intake side and its job is to spray the fuel in at the correct times. The ECU tells it when to spray. This is just a solenoid controlled device that only needs a power and earth to work.

Idle air control

 

The idle air control valves job is to maintain a constant idle speed it is positioned on the side of the throttle body and is put in to bypass the throttle butterfly to keep a constant idle rpm this is controlled by the ECU

O2 sensor ( lambda sensor)

The oxygen sensor is positioned in the exhaust system near the exhaust manifold and it reads the oxygen content in the exhaust fumes and tells the ECU whether the engine is running lean or rich. Some cars will have two which are placed before and after the catalytic converter so it knows if the catalytic converter is doing its job.

Map sensor

The manifold absolute pressure sensor is put in to measure the manifold pressure at all times so that the ECU knows how much fuel to add with the air. These sensors are mainly used in engines with EFI and also to the ECU how dense the air is inside the intake manifold.

Plenum chamber

 

The plenum which is the intake manifold side of the engine and is used to bring in the air from the throttle body and to distribute the air evenly to all of the cylinders so that the intake valve can supply it to the combustion chambers.

Camshaft & Crankshaft sensor

The cam and crank sensors are placed on the camshaft and crankshaft and tell the ECU at all times where the cam and crank are so it knows whether it is at TDC or BDC. Some engines use these sensors to know when to distribute the spark to the cylinders. They use a magnet or pickup on the gears which tell it every time the gear moves.

Who invented fuel injection and when?

The first use of fuel injection was by a Swedish engineer named Jonas Hesselman in 1925.

What does EFI stand for

The term EFI is short for Electronic Fuel Injection

Carburetor 1

Carburetor’s 1 

Indentifly the components in a carb?

The carburetor has many parts the helps the fuel come in and mix and supply fuel to the cylinder at a constant rate. This picture above shows that the fuel in brought in by the fuel line and filter which then goes into the float bowl then sucked up by a tube which delivers fuel into the throttle where the air is passing through which mixes the fuel and air into the combustion chamber. The throttle controls the air flow along side a venture. You can adjust the carburetor settings with the idle screws.

What is the purpose and how does  mechanical lift pump work?

The pump uses a spring which opens and closes a diaphragm which pumps the fuel from the inlet of the carburetor and the pushes it out the outlet. The spring has an arm which is connected to the camshaft and works on the cam lobe and as it lobe spins it pushes the spring up and down the faster the engine spins the faster the pump works and brings the fuel in and out.

What pressures would you get from these types of pump?

From these sort of pumps the pressures you would expect is about 4-5psi.

What is the four stroke cycle?

There are 4 strokes that a 4stroke engine needs to run which are:

Intake: Where the inlet valve opens bringing in the vaporized air/fuel mixture into the cylinder. The piston is moving down.

Compression: This is once the piston has hit bottom dead centre and starts moving upwards, the intake and exhaust valves are close which compresses the mixture until it is just about to the top.

Power: At about 8-10degrees before top dead centre the spark plug ignites the mixture causing an explosion inside the cylinder pushing down the piston causing the power to spin the crankshaft. The valves are closed until they hit the bottom.

Exhaust: Once the piston has hit bottom dead centre the exhaust valve opens as the piston moves up the cylinder it pushes the burnt gases out the exhaust. Then once it has hit top dead centre the exhaust valve closes and the intake opens to repeat the cycle.

What does S.I mean?

S.I is short for ‘spark ignition’ which only petrol engines use. This meaning that it uses spark to ignite the air/fuel mixture inside the combustion chamber unlike diesel engines

What does C.I mean?

C.I is short for ‘compression ignition’ which is the diesel engines way of igniting the air/fuel mixture inside the combustion chamber. It relies on the high compression and hot temperatures to ignite the mixture.

How does a bimetallic spring work in a automatic choke work?

This special spring is put inside the carburetor and is mounted opposite to a rod which turns the choke on and off. As the hot air is passed by it the heat bends the spring towards the contacts and once the engine was at operating temperature the spring will of bent into the contact which closed the choke.

What is the purpose of the float in the carburetor?

The float chamber (bowl) is the supply of fuel into the carburetor jet. As the fuel is used up there is a float inside the chamber and as the float drops it opens a needle valve which lets in more fuel into the chamber. But when the float chamber is filled the float rises and closes the needle valve which stops the fuel being let into the carburetor.

What are the holes in the emulsion tube for and how does it work?

The emulsion tube brings in the fuel from the float bowl and supply it up into the throttle chamber and as the throttle opens and there is more vacuum which sucks more of the fuel out of the holes in the emulsion tube. This helps to mix and atomize the fuel and air so the engine runs smooth.

What is the difference between petrol and diesel?

Petrol is lighter and has a lower boiling temperature then diesel, it also has a higher vapor pressure then diesel. But needs a spark to ignite under pressure.

Diesel is much heavier then petrol and also has a higher compression ratio compared to petrol. And has a higher boiling temperature and is a lot more dense then petrol and is ignited by the high compression in the combustion chamber.