Section 2 Operating Marine Diesel Engines
Section 2. Operating Marine Diesel Engines
Section 2:
Operating Marine Diesel
Engines
Learning Outcome 2
On completion of this section you should be able to start up, shut down and
monitor the operation of marine diesel engines, and recognise common
defects. |
The areas you will cover in this section are:
2.1 Checks and procedures before starting engines
2.2 Checks to be made if an engine fails to start
2.3 Interpreting the correct engine gauge readings
2.4 Warm up and cool down periods
2.5 Engine overheating symptoms
2.6 Engine slowing and stopping whilst vessel is underway
2.7 Identifying low oil pressure
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Section 2: Operating Marine Diesel Engines
2.1 Checks and procedures before
starting engines
The checks and procedures to be carried out before starting an engine
depend on:
e whether the engine has just been repaired or overhauled and
* whether you were the last person to run the engine.
The person with the Certificate of Competency to operate the machinery of
the vessel is the one who takes full responsibility and cannot transfer the
blame if something goes wrong. To cover yourself you must carry out pre-
departure checks and checks whilst the vessel is under way. The following
checks cover the engine.
Make sure that all work carried out to the engine has been
completed and that there are no tools, materials or parts lying on
the engine.
Ensure that there are no rags on the engine, especially the exhaust
area. Check the whole engine is free from fuel and lubricating oil.
Gear box is in neutral.
Sea water strainer is clean and open the sea connection valve and,
if fitted, the overboard discharge valve. Ensure there are no sea
water leaks.
If the vessel has been on the slip, it may be necessary to bleed off
any air at the sea water pump.
Water level in the fresh water header tank and ensure there are no
fresh water leaks.
Condition of all hoses. plus dee else
Sufficient fuel in the fuel tank for the intended voyage plus a
reserve amount of fuel.
Open the fuel tank drain valve and drain off any sediment and/or
water.
Open the fuel tank outlet valve.
If repairs have been carried out to the fuel system on the engine, it
may be necessary to prime the fuel system and bleed off any air.
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Section 2: Operating Marine Diesel Engines
If a water separator is fitted, dean off a any scene water.
Check the movement of the hand throttle.
Check the oil level in the sump shows full. In some engines, a
hand priming pump is fitted so the system may be primed and
prevent the major wear that takes place on starting an engine.
If the fuel injection pump has its own sump, check that the level in
the sight glass is at the upper line.
If a turbo charger is fitted and has its own lubricating system,
check that the level in the sight glass is at the upper line.
Check that the batteries are clean, charged, the electrolyte level is
above the plates and the terminals are clean and tight.
If it is possible, bar the engine over at least one complete
revolution.
This is carried out to ensure there is no fresh water in a cylinder
which could hydraulic the engine. It is also to ensure the engine
can turn over freely and nothing has been left in any of the
cylinders and all parts are back and are in proper working order.
Switch on power to the starter motor. Give the engine some
throttle. Engage the starter motor. The engine should rotate and
fire.
Immediately check the oil pressure.
Listen for any unusual noises, especially hard metallic knocks.
Check for fresh water, sea water, lubricating oil, fuel oil and
exhaust gas leaks. Ensure sea water is being discharged overboard.
The engine fresh water temperature will slowly rise and stabilise
at its operating temperature. The lubricating oil pressure will drop
from its initial starting pressure to its operating pressure.
The revolution counter will be indicating. The throttle should be
increased and decreased slightly to check its movement and that
the revolution counter is functioning.
With the engine at its operating temperature, check the colour of
the exhaust gas.
e Black smoke indicates excessive fuel for the amount of air and
caused by poor or insufficient combustion or engine overload.
® Blue smoke indicates lubricating oil is being burnt.
» White exhaust vapour indicates water or moisture. It may be
in the fuel, moisture in the air or from cold cylinder liner bores
when starting the engine.
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Section 2: Operating Marine Diesel Engines
2.2 If an engine fails to start
This section lists some reasons for engines failing to operate correctly. There
are many possibilities, so discuss these with your facilitator. Use this section
as a reference guide for later use, particularly when next on your operating
vessel
Engine will not start or is difficult to start
If the engine does not start, the causes are mainly in the supply of fuel and/or
air.
Remember:
1. A full charge of air needs to enter the cylinder.
2. This air must not escape as it is being compressed otherwise
insufficient heat is obtained to ignite the fuel.
3. Fuel must be injected in an atomised form into the cylinder at a precise
moment.
4. In addition, there must be no restriction in the flow of exhaust gases.
5. An engine may fail to start, be hard to start or on starting, be irregular in
its firing. It may be one or a combination of the above factors that is the
cause of these problems.
Engine not turning over quickly when the starter
motor is engaged
Battery capacity low
e Check that electrolyte level is above the plates.
e Try to start the engine on the other bank of batteries. Failing this, try to
start the engine on both banks of batteries. Never continue to use a
battery if the starter motor is sluggish. High discharge rates will buckle
the battery plates.
e Take the specific gravity of each cell of the battery. A fully charged
battery would have a specific gravity reading in each cell of 1.26 where
as a flat battery would give a reading of 1.10. The specific gravity reading
should not vary more than 0.030 between cells. A lower reading on one
cell usually indicates the battery needs replacing.
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Battery connections dirty
e Check that the connections to and on the battery is clean and tight. A
dirty or loose connection can be identified by the heat it generates.
Bad electrical connection to starter motor
e The starter motor draws the most load on the battery especially on diesel
engines because of their high compression ratios. The electrical
connections must therefore be tight and clean.
Faulty starter motor
e The starter motor could be burnt out or the pinion is not engaging with
the ring gear on the flywheel.
Incorrect grade of lubricating oil
e If the oil is too thick, the engine will not attain sufficient speed on the
starter motor to generate the amount of heat required on the compression
stroke to ignite the fuel.
Engine has been overhauled and is tight
e The parts of an overhauled engine are brought back to their correct
clearances. In these clearances there will be a number of high spots and
they will be worn away as the engine is run in. When the engine is run in,
1t will turn easily. The engine will not attain sufficient speed on the
starter motor to generate the amount of heat to ignite the fuel.
* There must be sufficient air and no restriction in the exhaust gas system.
Air cleaner restricted
* The air cleaner is choked restricting all or most of the air required by the
engine.
Exhaust gas restriction
e Could be caused by a bucket left on the outlet of a vertical exhaust pipe
to prevent rain water entering the engine or by the automatic flap valve
fitted for this purpose and is stuck in the closed position.
e Occasionally a baffle could come loose in a silencer and block the
passage of exhaust gas.
The air must be compressed to a high enough temperature to ignite the fuel.
This is usually due to low or poor compression. Compression pressure can
be checked by replacing each fuel injector in turn with a compression gauge.
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Section 2: Operating Marine Diesel Engines
Poor compression
Incorrect valve timing
e The inlet valve 1s not opening or closing at the correct moment in the
cycle because the engine has not been correctly timed after maintenance
work has been carried out. (The timing of the exhaust valve would be out
as well.)
Cylinder head gasket leaking
e Could be leaking between two cylinders, between a cylinder and the
outside of the engine or between a cylinder and a cooling water passage.
Fuel injector
e The fuel injector body may not be sealing properly in the cylinder head
allowing the compressed air to escape.
Incorrect tappet adjustment
e The tappet adjustment is such that there is no clearance between the inlet
or exhaust valve stem and the rocker arm. The inlet or exhaust valve is
not closing on the compression stroke. (This is referred to as riding).
Sticking valves
e The cam, through the cam follower, push rod and rocker arm, causes the
valve to open. The spring causes the valve to shut when the cam follower
moves off the lobe of the cam. A sticking valve is caused by combustion
being incomplete or the engine is (or has) overheated. Carbon finds its
way between the valve stem and guide until the spring cannot exert
enough pressure to close the valve. On the compression stroke, air will
pass the valve. It could be an inlet or exhaust valve.
Worn cylinder liner bores
e Normal wear takes place on the cylinder liner where the piston rings
come into contact with it. The wear is more pronounced near the
combustion space where the heat burns the lubricating oil. The wear is
also oval due to the thrust of the piston on the cylinder wall. The piston
rings will not seal against the cylinder liner walls and, on the
compression stroke, air will pass the piston rings into the crankcase.
Pitted valves and seats
e The exhaust valve and seat is prone to being pitted. Carbon, from
incomplete combustion, is hammered between the valve and seat when
the valve closes. On the compression stroke, air will pass the valve.
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Valves not seating correctly
e Can be caused by the head of the valve being bent on its stem due to the
head being too thin from continual grinding.
e Can also be caused by exhaust gases scouring the valve seat and/or head.
On the compression stroke, air will pass the inlet or exhaust valve.
Broken, worn or sticking piston rings
e The piston rings expand and seal against the cylinder liner walls. Normal
wear takes place and will in time become excessive. Piston rings are also
subject to breakage in service or when installing. They will also stick in
their grooves due to the carbon from incomplete combustion. In all cases
air will pass the piston rings on the combustion stroke into the crankcase.
Piston ring gaps in line
Installation of the piston rings is such that the gaps were not equally
separated or the ring gaps came into line during the running of the engine.
Piston ring gaps in line will cause the air from compression to enter the
crankcase.
Cold engine
e Although not poor compression, the air entering the engine and the
piston, cylinder liner and cylinder head are so cold that they take away
the heat of the compressed air before it can reach sufficient temperature
to ignite the fuel. If an engine is fitted with heater plugs, they can be
utilised. Other alternatives are to use an air heater or a starting fluid to
assist ignition of the fuel.
Fuel issues
Fuel tank empty
Fuel piping could develop a leak emptying the contents of the fuel tank
into the bilges.
Blocked fuel feed line
e The suction valve on the fuel tank could have vibrated closed or someone
could have closed the emergency fuel shut off valve.
Faulty fuel lift pump
e Fuel is not being delivered from the fuel tank to the engine. If it is of the
diaphragm type, the diaphragm could be perished or damaged.
e The drive to the pump could be damaged.
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Section 2: Operating Marine Diesel Engines
Choked fuel filter
The fuel filter has choked up with foreign matter as to prevent the full
flow of fuel. The filter may not have been changed at its recommended
period. A bad batch of fuel may have been received. The filter may
require changing at more frequent intervals until the system is clean.
Air in fuel system
Air is compressible where fuel is not. Air in a fuel system will cause the
engine to malfunction or not start. Air usually enters the fuel system
when repairs are carried out or where there is a fuel leak. This air must be
bled off until a bubble free fuel is obtained. Some fuel systems have a
manual priming handle on the fuel lift pump or on the fuel injection
pump. In addition, there are bleed valves throughout the system, such as
on filters or water separators.
Faulty fuel injection pump
The fuel pump is not delivering fuel to the injector.
Faulty fuel injectors
.
The valve pintle may be seized shut in its nozzle and no fuel is delivered
to the cylinder. The holes or orifices in the nozzle may be blocked. The
valve pintle may not be sealing on its seat causing misfiring and irregular
speed, particularly on light loads.
Incorrect fuel pump timing
The fuel is not being delivered to the fuel injector at the precise moment
in the cycle. The engine could have been overhauled and the timing of the
fuel pump was incorrectly carried out. It is possible for the timing to alter
whilst the engine is running due to insufficient tension on the fuel pump
coupling bolts.
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2.3 Engine gauge readings
Engine oil pressure
When started, the oil pressure in a cold engine can rise to 150% of its
normal operating pressure. As the engine reaches its normal operating
temperature, the oil thins out and the relief valve on the oil pump closes.
The oil will then drop to its normal operating pressure.
Oil pressures will differ between types and makes of engines. As a guide, on
a Detroit Diesel, normal oil pressure
at | is | with a minimum oil
pressure of
2100 rpm 276 to 414 kPa 207 kPa (30 psi).
(40 to 60 psi)
1200 rpm 207 to 414 kPa 124 kPa (18 psi)
(30 to 60 psi)
As can be seen, a lower minimum oil pressure is acceptable at a lower speed
compared to the minimum at a higher speed. This is due to the loadings, on
the bottom end bearings whilst on the power stroke, varying with speed.
Engine oil temperature
The oil temperature should not be permitted to rise more than 38° C (100°
F) as it will thin out and flow too freely. The oil pressure will also drop.
Depending upon the condition and efficiency of the oil cooler, a high sea
water temperature could cause the oil temperature to rise. If it rises towards
its maximum, the engine load must be reduced.
Fresh water temperature
The fresh water cooling system is designed to operate between specified
temperatures which will vary slightly between types and makes of engines.
One example is 85° C to 90° C (185° F to 195° F) and with the 103 kPa (15
psi) pressure cap in place on the header tank, the engine can operate
intermittently up to 96° C (205° F). The cooling water high temperature
alarm is set at 96° C (205° F).
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Depending upon the condition and efficiency of the fresh water cooler, a
high sea water temperature could cause the fresh water temperature to rise.
If it rises towards its maximum, the engine load must be reduced.
High cooling water temperatures increase the internal temperatures in the
engine and affect the lubrication of the engine. Excessive high cooling water
temperature causes overheating and subsequent seizure of the piston in the
cylinder liner.
—
Low cooling water temperatures tend to cool the cylinders too much and
retard the combustion process. This in turn will cause a smoky exhaust and
reduce the power output of the engine.
Practical Activity
Ask your facilitator to demonstrate the correct way to interpret engine
gauges.
Ensure you understand the relevant gauges that you are required to read as a
Marine Engine Driver Grade 3 during your vessel's operation.
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2.4 Warm up and cool down periods
Warm up and cool down periods are essential for assisting efficient engine
operation and maintenance. All metals in marine engines expand when
heated, and contract when cooled. Different metals will expand by different
amounts. Thin metals will expand quicker than thicker metals of the same
type when the same amount of heat is applied.
An engine consists of different types of metals and different thicknesses of
the same metal. Castings, such as the block, cylinder head and cylinder liner
must be uniformly heated up. If the heat is localised, this section will expand
at a much greater rate than the remainder of the part and will most likely
crack.
* On starting an engine, it is necessary for it to remain at idle speed until
the temperature normalises. The engine speed and load can then be
gradually increased. The fresh water cooling and the lubricating oil help
normalise the temperature of the engine. This is done by taking the heat
away from the hottest part of the engine to heat cooler parts of the engine.
e “The majority of wear takes place in an engine when it is started cold. One
of the purposes of lubricating oil is to put a thin film of oil between two
moving metallic parts. This separates the parts and reduces friction and
therefore wear.
e The power stroke places a load on the bottom end bearing. The lower the
revolutions of the engine, the lower the loading on the bottom end
bearing and the combustion temperature. On starting, the engine should
not be excessively speeded.
e The thermostat in the fresh water cooling system ensures that the engine
reaches its operating temperature quickly. This is done by distributing the
combustion heat to the cold parts of the engine, thereby minimising
unequal expansion.
e If an engine is on full load and stopped quickly, the cooling water
temperature will rise. This 1s due to the non-circulation of cooling fresh
water and the heat retained in the metallic parts of the engine. The
unequal contraction of these metallic parts has the same result as
expansion and could cause cracking.
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Section 2: Operating Marine Diesel Engines
Should the engine be fitted with a turbo charger, it is necessary to reduce
its speed in stages or slowly for two reasons:
Bearings of the turbo charger are lubricated by the main engine driven
lubricating oil pump. The engine, on stopping, will cease to supply the
lubricating oil to the turbo charger bearings. If time isn't taken for the
turbo charger to come to rest, damage could occur to the bearings.
The exhaust gas side of the turbo charger operates at a very high
temperature. It is preferable to reduce the temperature gradually rather
than quickly to prevent unequal contraction of the turbo charger parts as
it slows down.
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2.5 Engine overheating symptoms
In determining the cause of an engine overheating, consideration should be
given as to whether it is a gradual process or there is a sudden rise in fresh
water temperature.
An engine overheating can be identified by
e the fresh water cooling temperature gauge
e the exhaust temperature and
e by the operators sense of touch.
When tracing a fault it is helpful to follow the circuit or flow of the sea
water cooling and the fresh water cooling systems, and think what may be
wrong with each component that may cause overheating. Here are some
possibilities:
A gradual rise is where the temperature rises over a period of time caused
by wear; by a gradual build up of scale on the cooling water surfaces or a sea
water strainer gradually becoming clogged.
A sudden rise in temperature could be caused by the thermostat stuck in the
closed position, a pump impeller revolving on its shaft or the engine
overloaded.
When the engine 1s hot and the fresh water level in the header tank is low,
cold water should be introduced very slowly whilst the engine is running.
The cold water will then be heated sufficiently before it circulates around
the combustion space. Cold water suddenly coming into contact with the hot
cylinder liner and cylinder head may crack them.
Sea water temperature too high
An engine with poor compression usually results in the engine receiving
more fuel to get the required power. This results in overheating and a high
sea water temperature will increase the problem. The engine speed should be
reduced to bring the temperature back to its normal operating temperature.
Sea water intake rose or grid
Could become clogged over a period of time so there would be a gradual
increase in the fresh water cooling temperature. Reduce the engine speed
until the normal operating temperature is obtained.
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A plastic bag may get sucked onto the grid and a sudden rise in temperature
would occur. Gradually slow down the engine to reduce the heat slowly and
stop the engine. With no suction holding the plastic bag on the grid, and
with the vessel moving through the water, the plastic bag will come away
from the intake grid. Start the engine and let it idle until temperatures
stabilise.
Clogged sea water strainer
Could become clogged over a period of time so there would be a gradual
increase in the fresh water cooling temperature. Reduce the engine speed
gradually and stop the engine. Clean out the strainer. Start the engine and let
it idle until temperature stabilises.
Alternately the vessel may have voyaged through matter which quickly
clogged the strainer. Take the above action.
Thermostat not opening fully
When the engine is cold the thermostat is in the closed position. Water 1s
circulated through the engine only. As the engine reaches its operating
temperature, the thermostat opens and allows the water circulating through
the engine to pass through the fresh water cooler or the keel cooling pipes.
Should the thermostat stay in its closed position or not open fully, the engine
will overheat. Feel the pipe from the thermostat housing to the fresh water
cooler. This will indicate whether or not water is flowing through it. Reduce
the engine speed gradually and stop the engine. When the engine has cooled
down, replace the thermostat. Should you be at sea and have no replacement
thermostat, the engine can be run without a thermostat. Start the engine.
Faulty impeller in sea water pump
A faulty impeller in the sea water pump (such as the rubber one in a jabsco
pump) could be damaged. Damage usually occurs when the pump is run dry.
The discharge pipe would be warm and not at the same temperature as the
sea water. Also, there would be no (or reduced) sea water discharge
overboard. Reduce the engine speed gradually and stop the engine. Replace
the impeller.
Should you be at sea and have no replacement impeller, it may be possible
to reach port at reduced speed, if the impeller is only partially damaged and
can still pump some water. Alternately, a sea water hose from the fire pump
or the wash deck hose could be connected up to the system at the discharge
side of the sea water pump to get the vessel back to port.
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Keel cooling pipes not effective due to marine growth
This causes a gradual increase in the fresh water temperature. Reduce the
engine speed gradually until the normal operating speed is obtained. The
vessel will have to be slipped to clean the keel cooling pipes.
Air in sea water cooling system
On a lot of vessels, air is trapped in the sea water cooling system when the
vessel re-enters the water after slipping. With the engine stopped, the air can
be bled off by slackening off the backing plate on a jabsco pump or
loosening a join in the seawater cooling pipe on the suction side of the pump
that is below the water line. If it is a jabsco pump and it is run dry until the
engine overheats, the rubber impeller will be severely damaged.
Insufficient speed of sea water pump
On some vessels the sea water pump is belt driven from the engine. The
adjustment of the belt may cause it to slip. Reduce the engine speed
gradually and stop the engine. Adjust the belt tension. Start the engine and
let it idle until temperature stabilises.
It may be that the pump does not attain sufficient speed as the driver or
driven pulleys may be the wrong size. Reduce the engine speed gradually
until normal operating temperature is attained.
Faulty impeller in fresh water cooling pump
A faulty impeller in the fresh water pump could be damaged. Reduce the
engine speed gradually and stop the engine. Replace the impeller. Should
you be at sea and have no replacement impeller, it may be possible to reach
port at reduced speed if the impeller is only partially damaged and can still
pump some water.
Build up of scale on cylinder water jackets, etc.
Fresh water contains impurities. They come out of solution at high
temperatures and will adhere to hot surfaces. The hottest part of the engine
1s in the combustion space at the top of the cylinder. Scale will deposit on
the cylinder liner walls in this area, on the passages to the cylinder head and
around the exhaust valve. The scale will stop the transfer of heat from the
combustion process to the fresh water cooling and, in the case of passages,
Will restrict the flow. This will be a gradual process. Reduce the engine
speed until normal operating temperature is attained.
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Engine parts may be too tight causing friction
A new or overhauled engine normally runs hotter because it is tight. As the
engine is run in, the high spots disappear. The engine turns easily, thereby
reducing the operating temperature. Reduce the engine speed so that it runs
at its normal operating temperature.
Fresh water cooling level is too low
A leak has developed in the fresh water system causing a loss of water in the
header tank. Tt could be a leak in the piping, seal in the pump or a blown
cylinder head gasket. Reduce the engine speed gradually and if the fresh
water system is the unpressurised type, very slowly top up the header tank to
its correct level.
If the fresh water system is of the pressurised type, reduce the engine speed
gradually and stop the engine. Let the engine cool down further before
placing a rag over the header tank cap. Turn the cap anti-clockwise until 1t
reaches the position where the pressure is released. When the pressure is
released, remove the cap. Start the engine and very slowly top up the header
tank to its correct level.
If there is very little water in the header tank, it is advisable to stop the
engine and let the engine cool right down before adding fresh water.
If possible, the leak in the piping should be stopped or the pump seal
replaced.
Blown cylinder head gasket
A cylinder head gasket leaking will be indicated by bubbles in the header
tank. The extent of the leak will determine the amount of bubbles. When
checking for bubbles, remember the above for pressurised and unpressurised
systems. Whilst the engine is running, the pressures inside the cylinder
exceeds that of the leak and the water. The heat will turn the water into
steam and be discharged with the exhaust gases. However, when the engine
is stopped, there is no pressure in the cylinder. The header tank is above the
cylinder thereby putting pressure (a head) on the water. The water would
then flow through the leak in the cylinder head gasket into the cylinder.
Should the piston be below top dead centre, sufficient water could flow into
the cylinder and hydraulic it. The water level would drop in the header tank
and the procedure would be the same as that above. However, remember
that if the engine is stopped for a period of time, it may hydraulic the
cylinder.
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Air in fresh water cooling system
Not normally an overheating problem when the engine is running. Air can
get into the system when repairs are carried out and the cooling system is
refilled. On starting the engine, bubbles will be sighted in the header tank as
the air makes its way out. As the water replaces the air, the water level in the
header tank will drop. As it drops, it can be topped up slowly.
Low compression
Low compression causes the engine to overheat. Some of the heat in the
combustion gases by-passes the piston rings and goes into the crankcase.
The cooling water is not taking away the heat caused by combustion, and
overheating of the engine occurs. The engine speed should be gradually
reduced until the normal operating temperature is attained.
Engine overloaded
An engine that is overloaded will overheat. An engine can be overloaded by:
e a dirty hull
® a rope around the propeller
e a bent propeller blade or
e too large a pitch propeller.
The engine speed should be reduced until the normal operating temperature
is attained. To stop overheating, it would be necessary to clean the hull of
marine growth, remove the rope from the propeller, straighten the propeller
blade, alter the propeller pitch or replace the propeller with one of the
correct pitch.
Dirty or fouled fresh water cooler
The sea water discharged overboard would be restricted. It is unusual for the
cooler to be completely blocked. Reduce engine speed until normal
operating temperature is attained. Stop engine and clean the cooler or return
to port under reduced speed.
Fuel injection into cylinders may be too late
The timing of the fuel injector pump is out causing the fuel to be injected
into the cylinders too late which will cause the engine to overheat. Reduce
engine speed until normal operating temperature is attained. Stop engine and
adjust fuel pump timing.
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2.6 Slowing whilst under way
The engine slowing down and stopping is of concern to the Master as the
safety of the vessel may be in danger.
This may be caused by
e lack of maintenance
e pre-departure and under way checks not being carried out or
® not responding to early indications that something is wrong.
Once again, when considering the principles upon which a diesel engine
operates, it is very evident that if a fresh charge of air is drawn into the
cylinder and then compressed to the proper pressure, and fuel is injected into
this highly compressed air, combustion must follow. If the engine has been
running satisfactory and then slows down and stops, the causes are mainly in
the supply of fuel.
Fuel tank empty
Isolate empty fuel tank and use another fuel tank.
Fuel tank outlet Carry out temporary repair to pipe by placing a piece
| pipe split or of rubber around it, then a thin bit of metal to give
corroded and | the rubber some support and attach them with hose
losing all the fuel | clips. Isolate empty fuel tank and use another fuel
‘in the tank tank.
Fuel tank outlet
valve has vibrated
shut
| Open valve and tighten gland packing to stop valve
vibrating shut.
Emergency fuel
shut off valve has
been closed
Open valve.
| Water in the fuel | Drain off the water at the fuel tank and, if fitted, at
| the water separator.
Clogged fuel filter | Depending on the type of filter, clean the filter or
replace the disposable element.
Faulty fuel lift Repair or replace the pump.
pump
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Section 2: Operating Marine Diesel Engines
Cause Action |
Fuel pump The engine will misfire until the timing is that far out
couplings have as to cause the engine to stop. Retime the fuel pump.
slipped altering
the timing
The engine room | There will be insufficient air entering the engine
hatch is closed room and the engine will starve of air and stop. Reset
and the fire flaps | fire flaps in the open position.
are shut
Some engines can be stopped in an emergency by closing a flap over the air
intake. This flap could be accidentally close or malfunction and close. Reset
the flap in the open position.
Note: Most mechanical failures do not stop the engine unless it has to do
with the valve timing for all cylinders. A broken timing chain is an
example. Mechanical failures result in noise, probably a knocking
sound which will continue until the engine is stopped.
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Section 2: Operating Marine Diesel Engines
2.7 Identifying low oil pressure
The reduction in the normal operating pressure of lubricating oil can be a
gradual process or happen instantly. The loss of oil pressure will cause those
parts under the most load to fail first. This would be the bottom end
bearings, due to the load placed on them on the power stroke. By reducing
the engine speed, the load on the bearings is reduced. It there is still some
oil pressure there, the reduction in load may be sufficient to save them.
Should the oil pressure drop instantly, the engine must be stopped
immediately.
A vessel does not have to be fitted with a low oil pressure audible alarm
unless it is over 25 metres in length. However most vessels under this length
are fitted with some sort of alarm. No mechanical, electrical or electronic
piece of equipment is fully reliable, especially in a marine environment. A
low pressure oil alarm may develop a fault and not indicate. The engineer
therefore must rely on his or her senses to monitor the engine condition.
Insufficient level of oil in the sump
e May cause a fluctuation of the oil pressure as the vessel rolls, the pump
could lose suction and air enters it. Reduce speed and top up the sump to
the correct level.
Lubricating oil pump strainer clogged
e Not much of a problem these days as the additives in the oil keep the
foreign matter and sludge in suspension for the filter to remove. Will
usually be a gradual drop in pressure. If possible, clean the strainer.
Faulty lubricating oil pump
e If the drive to the pump has sheared, there would be no oil pressure at all.
The engine must be stopped immediately otherwise severe damage could
occur. Should the gears or rotors of the pump be worn or too much
clearance between them and the backing plate, there will be a gradual
drop in oil pressure. If the lower oil pressure is sufficient, voyage at
reduced speed back to port.
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Section 2: Operating Marine Diesel Engines
Faulty relief valve
o The pressure relief valve may be stuck in the open position or its spring
may have broken. A cold engine when started, will have a high oil
pressure which will cause the relief valve to open. The engine’s oil
pressure drops as the engine reaches its normal operating temperature and
the oil thins out. This results in the relief valve closing. Should the relief
valve stick in the open position or the spring break, the oil pressure will
drop below normal. Free up the sticking relief valve or replace the relief
valve spring.
Filter partially blocked
e With the filter being partially blocked, the flow of oil will gradually be
restricted. Lower oil pressure will occur and be indicated on the pressure
gauge until the filter by-pass valve opens. Replace the filter element or
clean the filter (centrifugal type).
Oil temperature too high
* A high oil temperature will thin the oil out causing it to run more easily
with a resulting drop in oil pressure. This could be caused by a worn
engine which would have fresh water overheating as well. Alternately, it
could be caused by a dirty oil cooler on the sea water side. Run the
engine at a slower speed until the normal operating oil pressure is
obtained and voyage home. Alternately, clean the tubes in the oil cooler.
Faulty oil pressure gauge
* A faulty oil pressure gauge could indicate a low oil pressure where in fact
the actual pressure is correct. If the oil pressure gauge is suspected, try
another one.
Fractured lubricating oil pipes
e Will result in a gradual or sudden drop in pressure if the pipe splits. If it
is possible, repair the leak. If the lower oil pressure is sufficient, voyage
at reduced speed back to port.
Water in the oil
e Water mixing with oil will result in emulsified oil. It is grey/white or
sometimes described as milky in colour. Emulsified oil loses its
lubricating properties. When a certain amount of emulsification takes
place, the oil pressure will drop below normal. Stop the water leak and
change the lubricating oil.
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Section 2: Operating Marine Diesel Engines
Fuel in the oil
* Fuel contamination will thin out the oil and it will run easily off the dip
stick. There will be a rise in the level in the sump. The dip stick will also
have a fuel smell. Fuel contaminated oil loses its lubricating properties
and the oil pressure will drop below normal. Stop the fuel leak and
change the lubricating oil.
Practical Activity
For this section, it is important that you have practical experience in
e carrying out checks
e interpreting engine gauge readings
® carrying out correct procedures once faults are identified.
This experience will also come with time and practice. There are many
different reasons and causes for malfunctions.
Your facilitator will arrange for you to have the necessary experience on
board a vessel. You should discuss the information discussed in this chapter
with them, as well as gaining from their own experience in the industry.
Ask questions on your facilitator’s experience with engines and actions they
have taken.
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Section 2: Operating Marine Diesel Engines
Check Your Progress
1. What steps would you take if the engine slowed during operation?
2. Describe 3 reasons for an engine not turning over quickly when the starter
motor is engaged.
3. List 3 possible causes of an overheating engine. Describe what action you
would take to avoid engine damage in each case.
Cause Action
= | =
4. Describe the actions you would take after identifying low oil pressure.
N
Check your answers in this section’s text and discuss with your
facilitator.
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Section 2: Operating Marine Diesel Engines
Assessment Criteria
Can you now:
(J carry out checks and procedures to be followed before starting the engine
(A carry out checks to be made if an engine fails to start
I] interpret the correct engine gauge readings
[I explain the reasons for warm up and cool-down periods
[I describe engine overheating symptoms and the response required to avoid
engine damage
CI describe actions to be taken if the engine slowed down and stopped while
the vessel was under way
[ carry out the correct procedure to avoid engine damage after identifying
low oil pressure
70 Learner’s Guide — ABF621 - Engineering Knowledge (MED 3)
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