Oil pump service
Lubrication of engine bearings
164 part two engines and engine systems
The engine-lubrication system is responsible for
distributing oil to all parts of the engine. While oil in
the engine reduces friction and prevents wear, it does
much more. Improved engine oils, together with the
design of engine-lubricating systems, have generally
extended the periods between services and also
increased the service life of engines.
Functions of lubricating oil
Engine-lubricating oil performs the following
1. minimises wear
2. reduces friction and power loss
3. removes heat
4. reduces engine noise
5. forms a seal
Figure 11.1 shows how the main parts of an engine are
lubricated by oil pumped to them from the oil pan. The
oil reaches the various parts through pipes, passages,
drillings, holes and grooves. These, together with the
oil pump, oil filter and oil pan, make up the lubricating
system of the engine.
The main parts of the engine are provided with
positive lubrication, as shown. They receive oil directly
under pressure, and so are referred to as being pressurefed. Other parts that are not as heavily loaded are
lubricated with oil that is sprayed through a hole or jet.
Some parts of the engine do not require pressure
lubrication. These receive lubrication from oil on its
way back to the oil pan. Other parts depend on the oil
mist that is present in the crankcase when the engine is
Oil minimises wear
With proper lubrication, all the parts that are subject to
wear are separated by a thin layer of oil. The oil
prevents metal-to-metal contact so that there is
minimum wear. This is illustrated in Figure 11.2 which
shows how oil is needed between the connecting-rod
bearings and the crankshaft journals, and also between
the pistons and cylinder walls.
Without proper lubrication, the bearings would
wear quickly and eventually fail, causing damage to
the crankshaft and other engine parts.
Shortage of oil on the cylinder walls would cause
excessive wear and scoring of the cylinders, pistons
and piston rings.
Lubricating oil from the oil pan is pumped throughout the engine
chapter eleven engine-lubricating systems
As it flows through the engine, the oil tends to carry
away any particles of carbon or foreign matter and take
them back to the oil pan. Heavier particles drop to the
bottom of the oil pan. Lighter particles are removed by
the oil filter.
Most of the cleaning is done by chemical
detergents in the oil which keep engine parts clean,
and by dispersants which hold particles suspended in
the oil so that they are not deposited on the internal
parts of the engine.
Oil fills the very small irregularities in the
surfaces – it reduces friction in bearings and
helps seal pistons and rings
Oil reduces friction and power loss
All the moving parts of the engine are provided with
oil, and this reduces the friction between surfaces that
are in contact. Less friction means less power loss
within the engine.
There is still some friction in the engine, but this is
fluid friction between the layers of oil, and is much
less than dry friction.
The lubricating system of an overhead-camshaft
engine is shown as a block diagram in Figure 11.3. The
arrows show how the oil flows in the various parts of
Figure 11.4 is a similar lubricating system, but this
is an engine diagram, which shows how the oil reaches
Oil removes heat
The oil is being continuously circulated throughout the
engine, and while it lubricates the various parts, it also
removes heat from them and carries it back to the oil
pan. Heat from the oil pan is dissipated into the
Some engines are fitted with an oil cooler. This is
used to transfer heat from the engine oil to the cooling
system, or to the atmosphere. This reduces the oil
Oil reduces engine noise
There is always some clearance between the bearings
and journals, and between other working parts. When
the load on a part is suddenly increased, the oil
between the parts acts as a cushion to absorb the shock
and reduce the noise.
Oil forms a seal
Piston rings must form a gas-tight seal between the
piston and the cylinder wall. The oil on the cylinders
helps by filling the very small irregularities in the
surfaces. At the same time, the oil on the cylinder
walls lubricates the pistons and rings.
Block diagram showing the oil flow in an
166 part two engines and engine systems
Engine-lubricating system for an overhead-camshaft engine
1 strainer, 2 suction pipe, 3 crescent oil pump, 4 regulator valve, 5 oil filter, 6 main oil gallery, 7 main-bearing
journal, 8 crankpin journal, 9 passage to rocker gear, 10 rocker arm, 11 exhaust rocker shaft, 12 camshaft MAZDA
the actual engine parts. In both diagrams, oil flow
starts at the oil pan and, after circulating through the
engine, returns to the oil pan.
The various parts of the lubricating system are
listed below. Using this as a reference, the oil flow
should be followed through the block diagram and also
through the engine diagram.
Oil circulates through the lubricating system as
1. Oil pump. The oil pump is driven by the engine. It
takes oil from the oil pan through the strainer and
suction pipe and delivers it to the filter. The
strainer prevents foreign matter from reaching the
2. Relief valve. The relief (or regulator) valve regulates the pressure in the system. When the pressure
specified for the engine is reached, the relief valve
opens to prevent any further increase in pressure.
Surplus oil is then bypassed to the intake side of the
3. Oil filter. All the oil which leaves the pump is
filtered before entering the engine. The filter
removes particles of carbon and any other matter in
the oil and so protects the engine.
chapter eleven engine-lubricating systems
The filter has a bypass valve which opens if the
filter becomes blocked. This allows unfiltered oil to
pass into the system so that the engine is not
starved of oil.
4. Main oil gallery. The main oil gallery is a passage
that runs the full length of the crankcase. A number
of drillings and passages from the gallery service
other parts of the lubrication system.
In Figure 11.4, a passage from the main oil
gallery carries oil to the overhead camshaft and
valve gear, and a drilling through each of the
crankcase webs supplies oil to the main bearings.
5. Crankshaft main bearings. Each of the five main
bearings is supplied with oil through a separate
drilling from the main oil gallery.
6. Connecting-rod bearings. Drillings in the
crankshaft carry oil from the main bearings to
the connecting-rod bearings. Some oil leaves the
connecting-rod bearings and is thrown around as a
mist, and this helps to lubricate the internal parts of
7. Oil jet. An oil jet is used to lubricate the cylinder
walls and pistons (Figure 11.5). A small hole in the
side of the connecting rod is arranged to line up
with the oil drilling in the crankpin journal. As this
occurs, a spray of oil is directed onto the cylinder
walls. This happens once in each crankshaft
8. Camshaft bearings. The camshaft receives its oil
supply from the main oil gallery. In the arrangement
shown in Figure 11.4, there are separate rocker
shafts for the intake and exhaust valves. The oil to
lubricate the camshaft bearings is carried through
the hollow rocker shaft to the camshaft bearing caps,
where drillings take it to the camshaft bearings.
9. Rocker shafts. Drillings in the rocker shafts
provide oil to the rocker arms and these, in turn,
have a small drilling to provide lubrication to the
cams (Figure 11.6).
oil in shaft
oil pool on
Lubrication of rocker arms and cams
10. Cams. As well as receiving oil directly from the
rocker arms, the cams and the other parts are
lubricated by splash. The cylinder head under the
camshaft is shaped to form an oil reservoir from
which oil is splashed by the cams to lubricate the
cam surfaces, valve stems and valve springs.
11. Timing chain. Where a timing chain is fitted, oil is
provided from the end camshaft bearing or similar
source so that the chain and sprockets are
12. Return oil. After lubricating the various
components, oil from the cylinder head drains
back to the oil pan through oil drain holes
provided for this purpose. Oil from the crankshaft
drops directly back to the oil pan.
There are three designs of oil pumps. The basic
arrangements are shown in Figure 11.7. They are:
1. gear pumps
2. crescent-type pumps
3. rotor pumps.
When a hole in the connecting rod aligns with
a hole in the crankpin, oil is sprayed onto the
cylinder wall to lubricate the piston and rings
■ Oil pumps can be driven by gears or by a chain, or
directly from the crankshaft.
168 part two engines and engine systems
(a) Gear pump
(b) Crescent pump
(c) Rotor pump
Three basic designs of oil pumps
A gear pump, as shown in Figure 11.8, has two gears:
a drive gear and a driven gear. The drive gear is fixed
to a shaft and is driven by gears from the engine’s
camshaft. The driven gear is mounted on a stationary
shaft and is rotated by the drive gear.
When assembled, the gears are contained within the
pump body by the lower cover. The strainer is attached
to the pump inlet, which is part of the cover, and
immersed in oil in the oil pan.
In operation, oil enters the pump inlet through the
strainer and is carried around between the gear teeth
and the body of the pump to the outlet, where it is
delivered from the top of the pump into the lubricating
The crescent pump shown in Figure 11.9 has an
external toothed gear meshed with an internal toothed
gear. Some of the teeth of the gears are in mesh, but
the others are separated by a crescent-shaped part of
the pump housing.
The pump is mounted on the front of the crankcase
with the inner gear on the end of the crankshaft, so that
the pump is driven directly from the crankshaft.
When the pump is operating, oil is taken in through
the intake port and is carried around between the gears
and the crescent to the outlet port.
■ The oil pump of the engine-lubricating system
shown in Figure 11.4 is a crescent-type pump.
Gear-type oil pump driven by a shaft
1 upper shaft, 2 pump body, 3 driven gear,
4 gear shaft, 5 drive gear, 6 cover, 7 strainer
The pump housing is bolted to the front of the
crankcase. It has an inner rotor and an outer rotor
(Figure 11.10). The inner rotor is mounted on the
crankshaft and so rotates whenever the engine is
running. The lobes of the inner rotor fit into the outer
rotor which is rotated in the housing.
chapter eleven engine-lubricating systems
An example of checking the clearance of the gears
in the housing is shown in Figure 11.9, where feeler
gauges are being used between the gear and the
Oil pump relief valve
Crescent oil pump – clearance can be
checked where shown and also between the
gears and crescent MAZDA
The oil pump is capable of supplying much more oil
than is needed to maintain a pressure in the lubricating
system. To prevent excessive pressure developing, a
relief valve is fitted to the oil pump or to the oil
The relief valve consists of a spring and plunger,
which opens and closes a port to regulate the flow of
oil. A simplified relief valve is shown in Figure 11.11.
It works like this:
1. When the engine is started, the pump supplies oil to
the system. At engine idle speed, the port is closed
by the plunger. All the oil from the pump enters the
system and provides a low oil pressure.
2. As engine speed increases, the pump speed also
increases and so more oil is delivered into the
system. This increases the pressure in the system.
Pressure acting on the top of the plunger moves it
down its bore.
3. When the system reaches a certain pressure, which
is determined by the strength of the plunger spring,
the plunger will have moved far enough to open the
4. Surplus oil, which is not needed to maintain
pressure in the system, will then pass through the
port and return to the intake side of the pump.
Rotor oil pump
1 cover, 2 inner rotor, 3 outer rotor, 4 gasket,
5 housing, 6 relief valve assembly HOLDEN LTD
5. The plunger will open and close the port, as needed,
to release surplus oil and limit the pressure in the
system. Whether the port is open or closed will
Oil is taken into the pump through an inlet pipe and
strainer and carried around between the lobes of the
rotors to the outlet port. A relief valve in the pump
body controls the pressure in the system.
Oil pump service
Under normal circumstances, an oil pump would only
be serviced during a complete engine overhaul.
The pump and regulator valve would be cleaned,
and the gears and housing checked for scores and
wear. The clearance between the gears and housing (or
rotor and housing) would be checked, as well as the
end clearance of the gears in the housing.
Operation of an oil pressure relief valve –
pressure on top of the plunger is opposed by
170 part two engines and engine systems
depend on the engine speed and the temperature of
the oil. It will also depend on the condition of the
■ A relief valve is located in the housing of the oil
pump shown in Figure 11.10.
Why the system has pressure
Pressure builds up in the system because the oil pump
maintains a supply of oil, and also because of the
restrictions provided by the small bearing clearances
etc, which prevent the oil from flowing readily back to
the oil pan.
With worn bearings and large clearances, or if a
relief valve is stuck open or has a faulty spring, the
pressure in the lubricating system will be low. If any of
these conditions occurs, the pump will be delivering to
its maximum capacity but will not be able to supply
enough oil to build up normal pressure.
■ Oil pressure depends on the pump delivering an
adequate supply of oil and the engine being in good
mechanical condition. A badly worn engine will
have low oil pressure.
Construction of a canister-type oil filter
During engine operation, carbon particles, dust and
small metal particles become mixed with the
lubricating oil. The oil filter keeps the oil clean by
removing these impurities which would otherwise find
their way through the oil passages to the bearings and
A sectioned oil filter is shown in Figure 11.12. It
consists of a metal canister with a pleated-paper
element. The element is porous to allow oil flow without restriction, but the pores are fine enough to filter out
the impurities in the oil. The canister is threaded on to a
tubular mounting on the engine block. A rubber ring
provides a seal between the filter and its mounting.
The filter has a non-return valve at the open end of
the canister which prevents oil from draining from the
filter when the engine is stopped. The valve is a rubber
disc that covers a ring of holes.
When the engine is running, oil flows into the filter
through the non-return valve holes to the outside of the
element. It passes through the element to the inside of
the canister, then back to the engine through the
A bypass valve inside the canister is a safety valve,
which opens to allow oil to go straight through the
filter should the element become blocked.
Replaceable filter element
The filter assembly in Figure 11.13 has a replaceable
filter element. The filter housing is bolted to the engine
block and the paper element is held in the housing by
the filter cover.
The oil flow in the filter is similar to that of a
Oil filter with a replaceable element
chapter eleven engine-lubricating systems
Full-flow and bypass filters
There are two filter arrangements: full-flow filters
and bypass filters. Full-flow filters are mainly used,
but some diesel engines have a full-flow filter as the
main oil filter, and a bypass filter as a supplementary
Figure 11.14 shows the principle of a full-flow oil
filter. All the oil delivered from the pump passes
through the filter on its way to the bearings and other
engine parts, so that only filtered oil is used for
lubrication. A bypass valve is located in the filter so
that if the filter becomes clogged, the valve will open
and oil will still be supplied to the system.
■ Full-flow filters operate at engine oil pressure and
must be correctly tightened during servicing to
avoid oil leaks.
The principle of a bypass filter is shown in Figure
11.15. This filters only a portion of the oil delivered
Principle of a full-flow oil filter – all the oil
entering the system is filtered
Principle of a bypass filter – some of the oil
from the pump is filtered and returned to the
from the pump to the oilways of the engine and it
operates at a lower pressure than a full-flow filter.
An oil line is tapped into the oil gallery and a
restricted amount of oil is allowed to flow through the
filter. The oil from the filter is not delivered into the
engine, but is bypassed and returned to the oil pan. In
this way, some oil is always being filtered, though not
directly on its way to the engine parts.
Oil coolers are heat exchangers, in which heat in the
oil is transferred either to the engine coolant, or to the
There are two designs of oil coolers:
1. oil-to-coolant coolers
2. oil-to-air coolers.
Oil-to-coolant oil cooler
Both oil and coolant flow through this type of cooler,
the two being separated by tubes or baffles of some
type. This enables heat to be transferred from the oil to
the coolant because the oil is at a higher temperature.
An oil cooler and oil filter assembly for a small
diesel engine is shown in Figure 11.16. Both the cooler
and the filter are installed on the oil filter mounting on
the cylinder block. With this arrangement, oil from the
oil gallery passes through the oil cooler before it enters
Oil-to-coolant type oil cooler and oil filter
172 part two engines and engine systems
the filter, so that oil leaving the filter has been both
cooled and filtered.
The cooler has external connections for the coolant
hoses that connect it to the engine’s cooling system.
heat is removed from the oil and its temperature is
The cooler is located in the engine compartment
where it will get an adequate flow of air, usually near
Oil-to-air oil cooler
This type of oil cooler is similar to a radiator in that
it has tubes and fins (Figure 11.17). Oil from the
lubrication system is circulated through the cooler, and
air is directed across the tubes and fins. In this way,
Lubrication system with oil-to-coolant cooler
A lubricating system for a small diesel engine is shown
in Figure 11.18. This has an oil-to-coolant type cooler.
The cooler is mounted to the engine block and the oil
filter is mounted on the cooler. Oil flows through the
cooler, then through the oil filter and on to the main oil
This system has other features that can be identified
in the illustration:
1. The oil pump is directly driven by the engine. It is
a rotor pump, referred to as a trochoid-type gear
2. The engine has balance shafts with bearings that are
pressure-fed from the main oil gallery.
3. The engine has a timing chain which is supplied
with oil from oil jets.
4. The system has piston-cooling jets which squirt oil
upwards into the pistons to cool the piston head.
5. The engine valves have hydraulic tappets which are
supplied with oil from the rocker shafts on top of
the cylinder head.
Oil-to-air type oil cooler
Engine lubricating system with an oil cooler and other features
chapter eleven engine-lubricating systems
V-type engine lubrication system
Figure 11.19 shows the lubricating system for a V-type
petrol engine. This has a lot of overhead gear, including two camshafts on each cylinder head. Oil has to be
supplied to four camshafts and also to the camshaft
The lubricating system includes an oil-to-coolant
1. Dry friction. Dry friction occurs between dry
surfaces. The lubricants used with bearings and on
sliding surfaces are used to convert dry friction to
2. Fluid friction. This is much less than dry friction
because the lubricant separates the moving
surfaces. Lubricated surfaces have some friction,
due to the molecules of oil which have to be
moved, but this is small compared to the friction if
the surfaces are dry.
Oil coolers are fitted to engines with turbochargers.
Turbochargers rotate at high speeds and are also
subjected to exhaust heat. For these reasons, a constant
flow of oil is provided to the turbocharger bearings to
both cool and lubricate.
An oil line from the oil gallery delivers the oil to
the turbocharger and a drain pipe returns the surplus
oil to the oil pan.
3. Boundary friction. This is a condition between dry
friction and fluid friction, where the surfaces are
almost unprotected, being coated only by an oily
film. The surfaces are actually in contact and are
not separated by a layer of oil.
Lubrication of engine bearings
■ Engine parts rely on boundary lubrication for a
short time when the engine is first started, before all
the lubricating passages have had time to fill. This is
a critical period that is responsible for engine wear.
The main purpose of a lubricant is to convert dry
friction to fluid friction. These and associated terms are
used in relation to lubrication and bearings as follows:
4. Boundary lubrication. The term is used in relation
to the very small amount of lubricant (or oil film)
that is on a shaft and bearing under boundary
Lubricating system for a V-type engine – it has an oil-to-coolant oil cooler
174 part two engines and engine systems
How engine bearings are lubricated
Bearings like the crankshaft bearings are supplied with
oil under pressure from an oil pump. The pressure oil
does not, as might be imagined, merely lift the shaft
off the bearings and cause it to float on the oil – the
rotation of the shaft is responsible for this. The shaft
collects layers of the oil delivered to the bearing and
carries them around with it.
The layers of oil are wedged between the shaft and
the bearing, so that the shaft is forced to rise (or float)
on the oil. Therefore it is shaft rotation that causes
floating to occur to prevent metal-to-metal contact, and
not the fact that oil is being delivered from the pump
under pressure. This is known as hydrodynamic
In engine lubrication diagrams, it can be seen that
the oil to the main crankshaft bearings enters at the top,
and so it cannot force the shaft upwards off the bearing. There is a very small clearance between the
crankshaft journal and its bearings, but it is sufficient
for hydrodynamic lubrication to take place.
Bearing, shaft and oil wedge
Figure 11.20 shows in sequence, from (a) to (d), the
action of a shaft as it commences to rotate in a bearing
and build up an oil wedge. The clearances between the
shaft and the bearing in the illustrations are
exaggerated to show this effect to advantage.
1. The shaft is stationary (Figure 11.20(a)). X indicates the area where only a thin film of oil covers
the shaft and bearing. This is the stage at which
boundary lubrication (and boundary friction) are
2. When the shaft commences to rotate (Figure
11.20(b)), it rolls to contact the bearing at Y. This is
still only boundary lubrication.
Principle of lubrication of a shaft and bearing – the shaft rotates in an anticlockwise
There is a thick layer of oil at the top, but little
oil at the bottom. As the shaft rotates, it acts like an
oil pump, causing pressure to build up at Y. This
forces the shaft towards the centre of the bearing.
3. The shaft speed has increased and it has picked up
layers of oil (Figure 11.20(c)). The shaft has been
forced over to the right so that it is now surrounded
4. The shaft runs floating on oil (Figure 11.20(d)).
Pressure due to rotation is greatest at Z, and this
keeps the shaft away from the bearing.
Crankcase ventilation is provided to remove vapours
from the crankcase and prevent their harmful effects.
Although ventilation is not directly a part of the
lubricating system, the engine oil would deteriorate if
the engine did not have an effective ventilating system.
During normal engine operation, some combustion
gases leak past the piston rings – this is called blowby.
Without ventilation, this would tend to pressurise the
crankcase. There could be traces of water, and some
unburnt fuel could reach the crankcase. All these
would have a deteriorating effect on the engine oil and
also on mechanical parts.
Early ventilation systems merely vented the
crankcase to the atmosphere, but this contributed to air
pollution. It was an inefficient method of ventilation
and did not keep out dust. Closed-crankcase ventilation
systems were therefore developed, and these became
known as positive crankcase ventilation.
Positive crankcase ventilation
The principle of positive crankcase ventilation (PCV)
is shown in Figure 11.21. This is a V-type engine.
There is an air hose from the clean-air side of the
engine’s air filter to the right valve cover, and a
vacuum hose which connects the PCV valve on the left
valve cover to the intake manifold.
Clean air is drawn into the crankcase, where it
mixes with the blowby gases. The gases are then
drawn from the crankcase through the PCV valve and
the vacuum hose into the intake manifold. They are
carried into the combustion chambers of the engine,
where they are burnt.
The positive crankcase ventilation valve (PCV valve)
is a flow-control valve that is fitted between the
chapter eleven engine-lubricating systems
The level on the dipstick should be checked
Changing the engine oil and filter
Positive crankcase ventilation (PCV) system
The general procedure for changing the oil and filter is
1. Warm up the engine.
crankcase and the manifold. It controls the air entering
the intake manifold at engine idle speed, so that
excessive air does not enter the manifold to upset
If this valve does not seal properly, or remains
open, the engine will idle badly.
If the valve sticks closed, harmful vapours will
remain in the crankcase to form acids, sludge etc and
give poor lubrication. Correct operation of this valve is
essential. If it sticks either open or closed, it should be
cleaned or replaced.
■ Crankcase ventilation is covered in Volume 2 with
other emission controls.
Lubricating-system maintenance consists of keeping a
check on the level of oil in the oil pan by means of the
dipstick, carrying out regular oil and filter changes,
and checking for possible oil leaks.
The oil level on the dipstick should be checked with
the vehicle in a level position, not on a slope. Remove
the dipstick, wipe it clean and also wipe the top of the
dipstick tube to remove dust. Reinsert the dipstick and
again remove it to check the level.
The oil level should be between the high and the
low marks, but close to the high mark (Figure 11.22).
Top up if necessary, but do not overfill.
■ Using the dipstick to check the engine oil level is a
simple check, but one that is most important.
2. Remove the oil filler cap from the valve cover.
3. Remove the drain plug from the oil pan and drain
the oil into a suitable container.
4. Check the condition of the plug washer, wipe
around the plug hole and replace the plug. Tighten
firmly, but do not overtighten.
5. Remove the oil filter and replace with a new one.
6. Pour sufficient oil into the filler hole in the valve
cover to show on the dipstick.
7. Start the engine and run it slowly until the filter fills
and the oil pressure warning light goes out, then
stop the engine.
8. Check the level of the oil on the dipstick and top up
to the full mark. The vehicle should be level.
9. Run the engine and check the filter seal for leaks.
Make a final check of the oil level.
■ Use the correct type and grade of oil recommended
by the vehicle manufacturer. (Lubricants are
covered in Chapter 32: Fuels, fluids and lubricants.)
Servicing oil filters
Most filters consist of a metal canister containing a
filter element. These are sometimes referred to as
‘throw-away’ filters because the complete filter is
unscrewed from its mounting on the engine and a new
one fitted in its place (Figure 11.23.)
An oil filter removing tool is shown in Figure
11.24. This has a band that fits around the filter
canister. The band tightens onto the canister as it is
being used, enabling the filter to be unscrewed from its
176 part two engines and engine systems
Replaceable oil filter that is threaded on to
An oil filter removing tool
Oil filters should be replaced at specified service
periods, for example, each 10 000 kilometres. When
installing a canister-type filter, observe the following,
as shown in Figure 11.25:
1. Clean the filter mounting.
2. Coat the rubber seal with oil.
Installing a canister-type oil filter
3. If possible, fill the filter with oil before fitting.
4. Screw the filter into place until the seal contacts the
5. Tighten, by hand, an extra one-half to threequarters of a turn.
element. The old filter element is discarded and, after
making sure that the filter housing is clean, a new filter
element is installed.
6. After running the engine, check for oil leaks.
Checking oil leaks
For a replaceable-element type filter, the outer
cover of the filter is removed to gain access to the filter
The most likely places for oil leaks are the oil filter,
the valve cover, and the oil pan. Where oil has coated
chapter eleven engine-lubricating systems
the engine and the leak is not easy to find, clean the
engine and then run it until the oil is warm. With the
parts of the engine clean and the oil thin, leaks should
be easier to find.
Oil pressure test
To check the oil pressure in the system, remove the oil
pressure switch from the engine block and install an
oil pressure gauge (Figure 11.26). Check the pressure
at idle and at higher engine speeds. Check the pressure
when the engine is hot and also when it is cold.
Low pressure could be caused by a broken reliefvalve spring, a worn pump not providing enough oil,
or worn engine bearings allowing too much oil flow.
High pressure could be due to a stuck relief valve.
Testing an oil pressure warning-light switch
table 11.1 General lubricating-system problems
Frequent topping up
Oil being burnt because of
Faulty gasket or seal
Filter not tight
Leak at the drain plug
Oil pan overfull
Coolant leak into cylinders
Overfilled when topping up
Coolant mixed with the oil
Pressure gauge connected to check the
engine oil pressure DAIHATSU
Badly worn piston rings
This is a pressure-operated switch that is screwed into
the main oil gallery. The switch will be ‘on’ when the
engine is stopped and there is no pressure in the
system. It will be switched ‘off’ by the pressure in
the system once the engine is started.
The switch can be checked with a test lamp
between the terminal and earth as shown in Figure
11.27. The lamp should light with the engine stopped
and go off when the engine is started.
If the switch is in order, the problem could be a
blown bulb or a faulty connection.
Oil not changed
Low oil pressure
Low oil level
Faulty relief valve
Worn oil pump
Worn engine bearings
Warning light shows
Loss of pressure due to oil
Warning light not
Faulty pressure switch or
Low oil pressure
Table 11.1 lists general problems that could occur with
an engine-lubricating system.
178 part two engines and engine systems
Pressure, pressure lubrication, dissipated, detergent,
dispersant, relief valve, regulator valve, bypass
valve, oil gallery, drillings, oil pump, oil jet, gear
pump, crescent-type pump, rotor pump, drive gear,
driven gear, filter element, canister, full-flow filter,
bypass filter, oil cooler, trochoid, crankcase
ventilation, blowby, positive crankcase ventilation,
PCV, PCV valve.
What is the purpose of the relief valve in the
What is the principle of a full-flow oil filter?
What is meant by a bypass oil filter?
What is the likely outcome if an oil filter
Why is crankcase ventilation necessary?
What is a positive crankcase ventilation system?
Describe how the connecting-rod bearings are
Where are oil coolers fitted?
In Figure 11.4, trace the flow of oil from the oil
pump to the various parts of the engine.
How are oil leaks located?
What functions does the engine oil perform?
How does oil reduce the power loss of an
Briefly describe the various types of enginelubricating systems.
Where are the most likely places for an oil leak?
Explain how an oil filter is changed.
How are the cylinder walls lubricated?
Name the different types of oil pumps.
What are the possible causes of low oil
Explain how a gear-type oil pump operates.
Where is the oil pump likely to be located on a
passenger car engine?
What could cause an overfull reading on the