This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.
Chapter
5
Fundamentals
of Engine
Construction
and Operation
After studying this chapter, you will be able to:
Q Describe each stroke of a four-stroke cycle engine.
Q Identify and explain the purposes of the major components of the engine compression system.
Q Explain the operating principles of liquid cooling systems.
Q Identify cooling system parts.
Q Explain the engine lubricating system.
Q Identify lubrication system parts.
Q List common oil classification systems.
Know These Terms
Balance shafts
Camshaft
Camshaft drive
mechanism
Compression stroke
Connecting rods
Coolant passages
Coolant pump
Coolant-recovery
system
Cooling system
Crankshaft
Cylinder head
Engine block
Engine coolant
Engine oil
Exhaust stroke
Exhaust valves
Intake stroke
Intake valves
Lifters
Lubrication system
Oil filter
Oil galleries
73
Oil pan
Oil pickup screen
Oil pump
Pistons
Power stroke
Pressure regulator
Push rods
Radiator
Radiator fan
Radiator pressure cap
Rocker arms
Serpentine belt
Thermostat
Valve timing
Valve train
Variable valve timing
Vibration damper
74
Auto Engine Performance and Driveability
Engine problems can have a major effect on vehicle
driveability. For example, without good compression or
proper valve timing, the engine will not properly operate.
This chapter covers the major engine components and
reviews engine operation.
Four-Stroke Cycle Engine Operation
One power cycle in an automotive engine is a four-stroke
process, which is why these engines are known as four-stroke
cycle engines. The piston moves up twice in the cylinder
and down twice in the cylinder for each power-producing
cycle. This requires two revolutions of the crankshaft. Refer to
Figure 5-1 as you read the following paragraphs. Some diesel
engines, however, use only two strokes rather than four.
The downward movement of the piston on the intake
stroke draws the air-fuel mixture into the cylinder through
the intake valve(s). When the piston reaches the bottom of
the intake stroke, the intake valves are closed. The piston
then moves up in the cylinder, compressing the air-fuel
mixture. This is called the compression stroke. When the
air-fuel mixture in the cylinder is ignited, the burning fuel
and oxygen produce heat. The heat causes the gases in the
cylinder to expand, forcing the piston down under pressure. This is called the power stroke.
The downward motion of the piston is transferred to
the connecting rod, which in turn pushes on the crankshaft.
The connecting rod and crankshaft arrangement changes
the linear piston movement into rotation of the crankshaft.
This rotational movement is used to move the vehicle.
When the piston reaches the bottom of the power
stroke, the exhaust valve is open. The exhaust stroke then
begins as the piston moves up the cylinder, pushing the
exhaust gases out of the open exhaust valve. One cycle is
now complete. The cycle then repeats.
1
Intake
Chapter 5
Fundamentals of Engine Construction and Operation
75
Engine Components
This section describes the major components of the
engine compression system. The compression system contains the parts that develop engine compression and allow
the heat energy in the burning air-fuel mixture to become
mechanical energy.
Q Engine block.
Q Pistons.
Q Rings.
Q Connecting rods.
Q Crankshaft.
Q Cylinder heads.
Q Valves and related components.
Q Valve train.
Q Harmonic balancers.
Q Balance shafts.
Although the exact design and number of engine components varies with the type of engine and number of cylinders, the basic components and their functions are the
same as described here.
Engine Block
The engine block is the basic support and attaching
point for all other engine parts. Engine blocks are made by
pouring molten cast iron, steel, or aluminum into molds,
Figure 5-2A. After the metal cools, the molding sand is
washed out and the block is machined to allow other parts
to be installed or attached, Figure 5-2B. The major parts
installed in or on the block are the pistons, crankshaft, camshaft, cylinder heads, and manifolds.
A
B
Figure 5-2. A—The engine block starts out as molten metal poured into a mold. B—The casting is then machined to accept and
support the other engine parts. (BMW, Honda)
Pistons and Rings
Pistons transfer the force of expanding combustion
gases to the connecting rods. They are made of aluminum
to reduce weight. Most automotive pistons have two compression rings and one oil ring, as shown in Figure 5-3.
Compression rings seal in the pressure created during the compression and power strokes. If this pressure is
allowed to leak out, the engine will not start or will have
severe power and driveability problems. The compression rings are installed at the top of the piston. A film of
oil between the compression ring and cylinder wall seals
pressure in the cylinder. This oil film is only about .001q
(.0025 mm) thick, but if it is removed, the engine will not
develop enough compression to start.
The oil-control ring is installed below the compression rings to prevent excessive oil consumption. During the
piston’s intake stroke, vacuum in the cylinder tries to pull
oil from the cylinder wall. To reduce oil loss, the oil-control
ring scrapes most of the oil from the cylinder wall when the
piston is moving down in the cylinder. A small amount of
oil passes by the oil-control ring to seal the compression
rings against the cylinder wall.
Connecting Rods and Crankshaft
The connecting rods are forged steel rods that connect
the piston to the crankshaft. They transfer the force from the
piston to the crankshaft. Each connecting rod is connected
to a piston by a piston pin. The rod is attached to the crank-
Head
3
Power
Ring
grooves
Compression
rings
Oil-control
ring
{
Skirt
A
2
Compression
4
Exhaust
Figure 5-1. The cycle shown here is typical of all four-stroke cycle engines: intake, compression, power, and exhaust.
B
Figure 5-3. The pistons and rings are the parts that most people associate with the compression system. A—This shows the
various parts of the piston. B—Compression and oil-control ring installation. Most engines with spark ignition use this type of ring
configuration.
76
Auto Engine Performance and Driveability
shaft by a bearing cap and bearing inserts that surround the
crankshaft journal. The piston pin and crankshaft bearings
allow the rod to move in relation to both the piston and
crankshaft. Refer to Figure 5-4.
The crankshaft converts the straight-line force from the
piston and connecting rod into rotary force. It is attached
to the engine block by bearing caps and bearings that surround the crankshaft journal, Figure 5-5. This design allows
the crankshaft to rotate inside of the bearings with minimal
friction. The bearing caps are held to the engine block by
two, four, or six bolts torqued to specifications.
Chapter 5
Fundamentals of Engine Construction and Operation
77
Coolant passages
Intake valves
Spark plug
Make sure the tab
on the bearing
fits tightly into
the matching
notch in the cap
Thrust
bearings
Main
bearing
caps
Bearing
inserts
(lower)
Cylinder Heads
The cylinder head contains the combustion chamber
for each cylinder and forms the top of the cylinder. Cylinder
heads contain the intake and exhaust valves and, in some
cases, the camshaft and lifters. They also contain oil galleries, coolant passages, and openings to allow the flow of
intake and exhaust gases. Cylinder heads are made from
either cast iron or aluminum. A sheet metal, cast aluminum,
or plastic valve cover is installed over the upper valve train
components. Figure 5-6 shows a typical cylinder head.
Coolant passages between the cylinder heads and
engine block must be sealed to prevent coolant leakage.
Also, the pressure of expanding combustion gases must
be contained within the cylinder. Head gaskets are used
between the head and engine block for these purposes.
They are thin and made from steel, copper, and fibers.
The cylinder head and head gasket are secured to the
block with head bolts. These must be torqued to specifications. A few engines have studs and nuts, rather than head
bolts.
Piston
Piston
Pin
Connecting
rod
Bolt
Bearing
inserts
Nut
Figure 5-4. The connecting rods attach the pistons to the
crankshaft. (Ford)
Make sure the tab
on the bearing
fits tightly into
the matching
notch in the block
Crankshaft
Bearing
inserts
(upper)
Combustion
chamber
Exhaust
valves
Figure 5-6. The cylinder head contains the valves and acts as a cap on the top of the engine. Along with the cylinders, it forms
combustion chambers for each cylinder. (BMW)
Figure 5-5. The crankshaft is the engine part that converts the
piston’s up-and-down (reciprocating) motion into rotary motion.
It delivers power to the drive train. (Ford)
Valves and Related Components
One or more intake valves are used to control the flow
of the air into each cylinder. One or more exhaust valves
are used to control the flow of exhaust gases out of each
cylinder. Valves also seal the cylinder during the compression and power strokes. They are occasionally called
mushroom valves due to their resemblance to a mushroom.
Intake and exhaust valves are identical in shape, but intake
valves are usually larger. Opening and closing of the valves
are controlled by the valve train.
The valve spring holds the valve against its seat, keeping it closed. Valve springs are always slightly compressed
when installed. This ensures that the valve closes tightly.
The spring is held to the valve by valve spring retainers. The
retainer is a cap which covers the spring. A locking device,
usually called a split keeper, locks the cap to the valve stem.
A valve and spring assembly is shown in Figure 5-7. The
assembly is held together by the pressure of valve spring
acting against the cylinder head.
The valve stem slides up and down in a valve guide.
The guide may be integral to the cylinder head or a removable insert. It keeps the valve steady and provides a smooth
surface on which the stem can slide. The oil seal at the top
of each valve stem prevents engine oil from entering the
combustion chamber. Without a seal, oil would be pulled
from the cylinder head, between the valve stem and guide,
and into the combustion chamber. The valve seal may be
an umbrella type or an O-ring installed between the valve
stem and valve retainer.
When the valve is in contact with its seat, heat is
transferred from the valve to the cylinder head. This transfer is most critical for exhaust valves, since they absorb
more heat of combustion. If the heat is not transferred
to the head, the valve may melt. Some valves are filled
with metallic sodium to further aid in heat transfer. The
intake valves are cooled by the incoming air and are not
as prone to damage.
The valve-to-seat contact is controlled by the valve
clearance. Valve clearance is the amount of looseness in the valve train between the camshaft and valve
stem. Valve clearance can sometimes be adjusted. Valve
clearance has more effect on valve life than on engine
performance.
In a cam-in-block engine, the camshaft lobes push on
valve lifters installed into bores machined into the block.
The motion is transferred through push rods and rocker
arms to the valves. The valve spring pressure is overcome
and the valves are forced open. The valve remains open
Split Keeper
Sleeve
Retainer
Spring
Valve stem seal
Valve Train
The valve train is the group of components that control
the opening and closing of the valves. Valve train operation is similar in both overhead camshaft and cam-in-block
engines. The engine crankshaft turns camshaft via a chain,
belt, or gear set. The camshaft controls the distance the
valves open and the duration of time over which they are
open. There is one camshaft lobe for each valve.
Valve
Figure 5-7. The valve assembly consists of the valve, valve
spring, retainers, stem lock, and oil seals. (Ford)
78
Auto Engine Performance and Driveability
until the camshaft lobe allows the valve spring to reseat
the valve. On overhead camshaft engines, the cam lobes
usually push directly on the valve rocker arm, Figure 5-8.
There are no push rods.
Valve Timing
The valves must open and close in proper relation to
the movement of the piston or the engine will not run. This
relationship is called valve timing, not to be confused with
ignition timing. Valve timing is determined by the relative
positions of the crankshaft and camshaft. The intake valve
must also open wide enough and long enough to allow the
air-fuel mixture to get into the cylinder. The exhaust valve
must do the same to allow the exhaust gases to get out of
the cylinder.
Lift is how wide the valve opens. Duration is the
amount of time that the valve stays open. Overlap is the
amount of time that both intake and exhaust valves are
open. Lift and duration are determined by the shape of the
camshaft lobes. Valve timing, lift, and duration have a big
effect on engine driveability.
The crankshaft always turns two complete revolutions
for every one revolution of the camshaft. This is because any
cylinder in a four-stroke cycle engine, whether gasoline or
diesel, requires two complete revolutions of the crankshaft
to complete all four cycles. However, each valve in the
engine opens only once during all four strokes. To accomplish this, the driving gear on the crankshaft always has half
the number of teeth as the driven gear on the camshaft.
Lash
adjuster
Valve Lifters
Valve lifters transmit the motion of the camshaft lobes
to the push rods or rocker arms. Lifters can be mechanical
or hydraulic. Mechanical, or solid lifters, must be periodically adjusted. Hydraulic lifters are self adjusting.
A typical hydraulic lifter is shown in Figure 5-9. The
outer lifter body contacts the camshaft lobe. The inner
piston (plunger) contacts the push rod or rocker arm. The
space between the lifter body and the plunger is filled with
engine oil. This oil is supplied by the lubrication system
through a small passage.
When the camshaft lobe pushes the lifter body upward,
the oil passage into the lifter is sealed off. Since the oil cannot escape or compress, the hydraulic lifter acts as a solid
unit and opens the valve. When the cam lobe allows the
lifter to move down, the lifter oil passage is again open and
oil can flow into the lifter. Engine oil pressure pushes the
plunger upward to remove any valve train clearance, but
does not have enough force to open the valve.
The friction between the lobes and lifters is the highest
friction in the engine and can cause the camshaft and lifters
to rapidly wear out. To reduce friction, the camshaft lobes
are tapered and the lifters offset. This causes the lifters to
rotate as they are pushed up by the lobe. This rolling action
between the lobe and lifter helps the lobes to evenly wear.
To further reduce friction, many late model engines use
roller lifters. A roller is installed on the bottom of the lifter
and turns with the lobe as the camshaft rotates.
Chapter 5
Fundamentals of Engine Construction and Operation
On overhead cam engines, the camshaft is installed
on top of the cylinder head. It opens the valves from above.
In some overhead cam engines, the lifter is placed between
the cam lobe and the rocker arm. In many cases, the rocker
arm is directly operated by the camshaft. A hydraulic lash
adjuster, similar in operation to a hydraulic lifter, maintains
the proper valve clearance. See Figure 5-10.
Camshaft
gear
Camshaft Drive Mechanisms
To maintain the relationship between the valves and
pistons, one of three types of camshaft drive mechanisms
is used. In all cases, the gear or sprocket on the crankshaft
has exactly half the number of teeth on the camshaft gear
or sprocket. This causes the camshaft to turn at exactly half
of the crankshaft speed.
A few vehicles use a gear drive, Figure 5-11. This type
of drive has two meshing gears. The crankshaft gear rotates
to drive the camshaft gear.
The majority of overhead valve, cam-in-block engines
use a chain drive, Figure 5-12. The crankshaft gear drives
the chain. The chain then drives the camshaft gear.
A few overhead camshaft engines use a chain drive.
However, most overhead camshaft engines use a belt drive,
Figure 5-13. In this design, the belt is driven by a crankshaft
sprocket. The belt then drives the camshaft sprocket. On
these designs, the belt often drives the water pump and oil
pump. Some overhead camshaft engines use a system that
is a combination of chain and belt drives.
Push Rods and Rocker Arms
Variable Valve Timing Devices
Push rods are used only on cam-in-block engines.
They transmit the lifter motion to the rocker arm. Many
push rods are hollow. Oil from the lifter flows through them
to lubricate the rest of the valve train. Rocker arms are pivoting levers that convert the upward movement of the push
rod or lifter into downward movement of the valve.
In the past, the valve timing set by the relationship
of the drive and driven sprockets or gears could not be
changed once the engine was assembled. An increasing
Valve
rocker
79
Crankshaft
gear
Timing marks
Figure 5-11. A few spark-ignition engines use gears as the camshaft drive mechanism. Gear drive is more common in diesel
engines.
Camshaft
gear
Cam
Push rod cup
Metering valve disk
Roller
follower
Check valve
Oil hole
Lock
ring
Plunger
Body
Check valve spring
Plunger
Plunger
spring
Check
ball
Spring
Check valve
retainer
Chain
Plunger spring
Crankshaft
gear
Body
Valve
stem
Check ball
retainer
Figure 5-8. The overhead camshaft valve train allows quicker
valve response with less play and friction between the components. Overhead camshafts are either belt or chain driven.
(Subaru)
Timing
marks
Figure 5-9. Hydraulic lifters use the engine oil pressure to automatically eliminate play from the valve train. Hydraulic lifters are
used on almost all cam-in-block engines. (Ford)
Hydraulic
lash adjuster
Figure 5-10. Lash adjusters are used in the valve train for an
overhead camshaft engine. They use the same principle as
the hydraulic lifter, but are installed on the rocker arm or on the
opposite side of the valve stem. (Ford)
Figure 5-12. Chain camshaft drive mechanisms are most common on cam-in-block engines. However, some overhead camshaft engines also have chain camshaft drives. Note the timing
marks on both the camshaft and crankshaft timing gears.
80
Auto Engine Performance and Driveability
number of engines have some form of variable valve timing.
Variable valve timing allows the timing of the valve opening
and closing to be varied based on driving conditions. Two
general types of variable valve timing are used on engines:
Q Camshaft timing adjustment. These adjusters are
mounted on the end of the camshaft where it is fastened to the driven sprocket or gear.
Q Camshaft lift and duration adjustment. These adjusters
are mounted at the camshaft lobes and rocker arms.
The vehicle computer operates the adjusters based on sensor inputs. The types of variable valve timing devices are
discussed in more detail in Chapter 10.
Camshaft
sprocket
Timing mark
Stationary
mark
Belt
Vibration Damper
When the engine cylinders fire, force is transmitted
to the crankshaft. When it receives this force, part of the
crankshaft tends to rotate before the rest of the crankshaft.
This causes a twisting of the crankshaft. When the force is
removed, the partially twisted shaft unwinds. This unwinding action, although minute, causes what is known as torsional vibration. To stop the vibration, a vibration damper,
sometimes called a harmonic balancer, is attached to the
front of the crankshaft. It consists of two heavy rings connected by rubber plugs, spring-loaded friction discs, or a
combination of the two.
When a cylinder fires and the crankshaft speeds up,
the outer ring of the damper has a tendency not to rotate. As
a result, the rubber connecting the two rings of the damper
flexes. As the crankshaft tries to unwind after the cylinder
has fired, the outer ring of the damper again tends not to
rotate in the opposite direction and the rubber flexes. The
unwinding force of the crankshaft is cancelled out by the
damper. On some newer engines, the crankshaft pulley is
an integral part of the balancer.
The engine flywheel also absorbs vibration. The
flywheel used with manual transmissions is heavy and
absorbs vibration. Automatic transmission flywheels are
lightweight steel stampings. The torque converter absorbs
most of the vibration.
Balance Shafts
In some engines, one or more balance shafts are
added to counterbalance vertical and torsional vibrations.
A balance shaft has offset weights that rotate in the opposite
direction of the crankshaft. These shafts are either turned
by the camshaft through direct gearing or by the crankshaft
through a belt or chain. Balance shafts help to provide a
smoother idle and less vibration from the engine.
Chapter 5
Fundamentals of Engine Construction and Operation
due to the tighter-than-normal clearances between moving
parts. An excessively hot engine tends to ping, diesel, or be
hard to start. It may also be hot enough to melt the exhaust
valves. This is usually called valve burning.
Some of the engine heat is removed by the exhaust
gases and some radiates out of the engine block and heads.
The rest of the heat must be removed by the cooling system.
The amount of heat removed must be controlled so that the
engine does not run cooler than its normal operating temperature. An engine that runs too cold wastes fuel, drives
poorly, pollutes the air, and quickly wears out.
All cooling systems remove excess heat from the
engine and transfer it to the surrounding air. The two main
kinds of cooling systems are liquid cooling and direct air
cooling. In liquid cooling, the heat is absorbed by a liquid,
which then transfers it to the air. In direct air cooling, the
heat is directly transferred to the air.
Lower (return)
radiator hose
Engine oil
cooler lines
81
Liquid Cooling
All cars and light trucks manufactured today have a
liquid cooling system. The engine block and cylinder head
has many internal passages through which coolant circulates. The coolant is moved through the cooling system by
a pump. As the coolant circulates through the passages,
it picks up heat from the surrounding metal. The coolant
then flows from the engine into the radiator. As the coolant travels through the radiator, heat is transferred from the
coolant to the air passing through the radiator. A fan draws
air through the radiator at low speeds. At higher speeds,
the movement of the vehicle forces air through the radiator. The cooled liquid then returns to the engine to pick up
more heat. Figure 5-14 shows a typical cooling system.
Engine Coolant. The engine coolant is the medium of
heat transfer. It must be able to absorb and release heat
without damaging any cooling system parts. Engine coolant
Heater hoses
Coolant pump
Oil filter
In-tank heat
exchanger
Heater core
Radiator
Coolant first flows through
the heads and then block
Tensioner
Engine-Related Systems That Can
Affect Driveability
Stationary mark
Timing mark
The following sections cover systems related to the
engine that can affect driveability. These systems are all
part of the overall basic engine and affect engine operation
if they are not properly operating.
Fan and motor
In-tank heat
exchanger
Cooling System
Crankshaft
sprocket
Figure 5-13. Belt camshaft drive mechanisms are used on
overhead camshaft engines. Some dual overhead camshaft
engines use a combination belt and chain system to drive the
camshafts.
The cooling system is a set of components that remove
unwanted engine heat and regulate engine temperature.
A cooling system is needed because not all of the heat
of combustion creates pressure to move the pistons. The
excess heat must be removed to prevent engine damage.
Even a slightly overheating engine experiences excess wear
Upper radiator
hose
Thermostat
housing
Transaxle fluid
cooler lines
Figure 5-14. Components of a typical cooling system. As coolant circulates through the engine, it picks up heat. This heat is transferred to the air by the radiator.
82
is a mixture of antifreeze and water. There are many types
of antifreeze. Some contain ethylene glycol or propylene
glycol. Also included are corrosion inhibitors to reduce
rust and corrosion of the engine block and radiator. Small
amounts of water-soluble oils are added to lubricate seals
and moving parts. Some antifreeze solutions use organic
acid technology (OAT) to lengthen the life of the coolant.
Pure ethylene glycol freezes at about 9oF (–13oC) and
water freezes at 32oF (0oC). When ethylene glycol and
water are mixed, however, the freezing point of the mixture is lower than either liquid alone. A 50:50 mixture of
ethylene glycol and water freezes at about –35oF (–37oC).
A mixture of 2/3 ethylene glycol and 1/3 water freezes at
about –67oF (–55oC). A 50:50 mixture of propylene glycol
and water freezes at about –26oF (–32oC). Most engine
manufacturers recommend a 50:50 mix of either ethylene
glycol or propylene glycol antifreeze and water.
A mixture of antifreeze and water has a higher boiling point than plain water. A 50:50 mixture boils at about
222oF (106oC). This gives added boil-over protection for
summer driving. Up to a 70:30 mixture of antifreeze and
water is sometimes used in severe climates and operating
conditions.
Antifreeze is colored with dyes. Color does not determine whether a particular antifreeze is suitable for a particular engine. Consult the service information for a vehicle
to determine which antifreeze to use.
Warning: Most antifreeze is poisonous to
humans and animals. Ingesting a very small
amount of antifreeze can lead to kidney
failure and death.
Coolant Pump. The coolant pump, or water pump,
consists of a cast iron or aluminum housing containing an impeller. The impeller is constructed with blades,
Figure 5-15. As the impeller rotates, coolant is thrown to
the outside of the impeller. This type of pump is known as
a centrifugal pump. It is capable of circulating several hundred gallons of coolant per hour at about 1 psi or 2 psi.
The pump intake is connected by a flexible hose to
the bottom of the vehicle radiator. Coolant is drawn into
the center of the rotating pump by suction. The coolant
is thrown outward by centrifugal force. Passages in the
pump and engine direct the coolant through the block and
heads.
Coolant Passages. Internal coolant passages, or water
jackets, are cast into the block and heads during manufacture. Coolant is pushed through the coolant passages by
the coolant pump. The coolant absorbs heat before exiting
through the top of the engine. Passages near the hottest
parts of the engine, such as near the valves and cylinder
walls, are designed so that more coolant flows through
them. Some internal coolant passages have external holes
for manufacturing purposes. These are sealed with metal
plugs called core plugs, or freeze plugs, Figure 5-16. Core
plugs may be pressed in or threaded.
Auto Engine Performance and Driveability
Drive pulley
Housing
Coolant is
thrown
outward
by the impeller
Chapter 5
Fundamentals of Engine Construction and Operation
is shut off until the coolant temperature falls to a certain
point. In addition, the fan is turned on any time the air
conditioner compressor is operating, no matter what the
coolant temperature.
Some longitudinal engines have belt-driven fans.
These fans are usually installed on the end of the coolant
pump shaft so that the same pulley drives the pump and
the fan. Many belt-driven fans have a fluid clutch installed
between the drive pulley and fan assembly, Figure 5-18.
Fan
blades
83
Serpentine belt
Coolant
pump
Fan clutch
Drive
pulley
Figure 5-18. Some vehicles have belt-driven fans. The fan clutch
allows the fan to freewheel at highway speed. This reduces the
load on the engine.
Inlet
(lower radiator
hose connection)
Impeller
Typical core
plug locations
Figure 5-15. The coolant pump uses an impeller to move the
coolant through the engine. Coolant pumps are either belt- or
gear-driven.
Radiator. The radiator is a heat exchanger consisting
of tubes and fins. As the coolant flows through the tubes,
heat is transferred to the fins. The fins then transfer the heat
to the air passing through the radiator. In most vehicles, the
radiator is capable of removing more heat than the engine
can produce. Actual radiator efficiency depends on the
flow rate of the coolant and the outside air temperature.
Most radiators are cross-flow radiators. In this design,
coolant flows from one side of the radiator to the other.
Tanks on the left and right sides of the radiator direct coolant into the radiator tubes or to an outlet that leads back to
the engine.
Radiators used on cars with automatic transmissions/
transaxles have a heat exchanger mounted in the radiator
to cool the transmission fluid. Hydraulic pressure in the
transmission/transaxle forces the fluid through the heat
exchanger. The fluid, which is at a higher temperature than
the coolant, gives up heat to the engine coolant. The transmission cooler is always mounted in the radiator tank that
feeds coolant back into the engine.
Radiator Fan. The radiator fan draws extra air through
the radiator to aid in heat transfer at low speeds. Most
fans are electric. See Figure 5-17. The fan is controlled by
either thermostatic switches installed in a passage of the
cooling system or through the engine control computer.
The fan remains off until the coolant temperature reaches a
certain point. The fan will continue to run after the engine
Figure 5-16. Core plugs are installed in various locations in the
front, sides, and rear of the block. The holes sealed by these
plugs are used to remove molding sand after the block is cast.
(Ford)
Crossflow
radiator
Air-temperature-sensing
switch
The fluid clutch allows the fan to freewheel, or not be
driven, at higher speeds when it is no longer needed. Some
fluid-clutch fans contain a thermostat that prevents the fan
from operating until the engine warms up. Other fluidclutch fans contain a flow-control solenoid. The solenoid
is operated by the vehicle computer based on temperature
sensor inputs.
Radiator Pressure Cap. The radiator pressure cap
is a valve that allows pressure to build up in the cooling
system. See Figure 5-19. It does so by using spring pressure
to hold a seal against the radiator filler neck. The spring is
calibrated to produce the proper system pressure. As the
engine heats up, coolant pressure builds until it overcomes
spring pressure and opens the valve. When the excess pressure is released, the spring closes the valve.
Fan
shroud
Electric
fan motor
Automatic
transmission
oil cooler
fittings
Radiator fan
switch
Enlarged
view—note polarity
Figure 5-17. One or more electric fans are used on all frontwheel and many rear-wheel drive vehicles. The electric fan
allows for better control of fan operation as well as more available horsepower from the engine. (Chrysler)
Figure 5-19. Radiator pressure caps are not a frequent source
of driveability or engine problems; however, a faulty cap can
cause diminished overheating protection. Never open a radiator
pressure cap when the cooling system is under pressure.
84
Auto Engine Performance and Driveability
The cooling system is pressurized to raise the boiling
point of the coolant. The boiling point of any liquid goes
up as the pressure is increased. For every 1 psi (6.9 kPa)
increase in pressure, the coolant boiling point increases by
3oF (1.7oC). Therefore, a 15 psi (105 kPa) pressure cap will
raise the boiling point of the coolant by 45oF (25.5oC).
Coolant-Recovery System. The coolant-recovery
system is designed to keep the cooling system as full as
possible at all times. The system consists of a tank connected by a hose to the radiator overflow neck, as shown
in Figure 5-20. The plastic tank is called the recovery tank.
Coolant that is pushed out of the radiator as the engine
heats up enters the recovery tank. When the cooling system
loses heat, a lower pressure is created in the radiator. The
difference between this pressure and atmospheric pressure
draws coolant from the recovery tank into the radiator.
Warning: Some coolant-recovery systems
are pressurized. The cap on the recovery
tank is a pressure cap like the one found on
the radiator. Never open a pressurized recovery tank
if the cooling system is under pressure.
Thermostat. The thermostat helps the engine to quickly
warm up by keeping coolant from circulating through the
radiator when the engine is cold. The thermostat is located
at the engine outlet gooseneck. This is where coolant leaves
the engine on its way to the radiator.
The thermostat consists of a heat-sensitive material,
such as wax, sealed in a chamber with a piston at one end.
The piston is attached to a valve that opens or closes the
thermostat to control coolant flow, Figure 5-21.
Recovery tank
Add
coolant
here
Fill levels
To radiator overflow neck
Figure 5-20. The coolant reservoir tank is usually mounted in
a conspicuous location and can be used as a quick diagnostic
tool. Bubbles in the reservoir bottle while the engine is running
is a good indication of severe engine problems. Most tanks are
not pressurized. Never open a pressurized tank when it is under
pressure.
Flange
Piston
Nut
Flange seal
Frame
Valve seat
Teflon seal
Valve
Coil spring
Wax pellet
Rubber diaphragm
Figure 5-21. Parts of a typical thermostat. Most engines use
a thermostat with an opening range between 190–195oF
(87.8–90.6oC).
When the coolant is cold, the wax is contracted and
holds the piston in the closed position. As the coolant warms
up and circulates under the thermostat, the wax expands
and pushes on the piston. This cracks the valve open and
allows coolant to begin circulating through the radiator.
As the coolant continues to warm up, the valve continues
to open until the wide-open temperature is reached. The
thermostat has no effect on engine temperature once the
coolant temperature is at or above the thermostat’s wideopen temperature.
Most engines use a thermostat with a wide-open
temperature of between 190–195oF (87.8–90.6oC). In very
cold weather, the thermostat may not fully open. Especially
when the vehicle is only operated for a short period of time,
the coolant may never reach the wide-open temperature.
Hoses and Tubing. The radiator is fixed to the chassis
and stationary. However, the engine moves on its mounts
as torque increases and decreases. Therefore, the radiator
is usually connected to the engine by flexible hoses. These
hoses are made of rubber or neoprene molded around a
fiber mesh. Clamps are used to secure the hoses to the
radiator and engine.
Some engines have a bypass hose that allows the coolant to circulate inside the engine until the thermostat opens.
On other engines, the bypass is built into the engine casting or the bypass system is the heater core and hoses. The
bypass system prevents damage to rapidly heating parts,
such as exhaust valves or cylinder walls, by allowing coolant to circulate past the parts before the thermostat opens.
Some cooling systems have fixed metal tubing to route
coolant along straight runs. The tubing is either directly
connected to components or connected via a flexible hose.
This tubing is made of soft steel or aluminum.
Many cooling systems also have one or more small
bleeder valves. If a portion of the cooling system is higher
than the radiator fill cap, the system will have at least one
bleeder valve. Bleeder valves are used to remove air from
Chapter 5
Fundamentals of Engine Construction and Operation
the cooling system during service. Pockets of air in the cooling system can block coolant flow, resulting in hot spots or
engine overheating.
Engine Belt. An engine belt drives the coolant pump
and other engine accessories. The belt is called a serpentine
belt because it winds around several pulleys, Figure 5-22.
It is driven by a pulley on the front of the crankshaft. The
belt must be in good condition and properly adjusted. Most
engines have an automatic tensioner to keep the serpentine
belt properly adjusted.
Excessive tightness in the belt places a heavy load on
the bearings in the coolant pump and possibly the crankshaft bearings. This will cause premature wear. Looseness
in the belt permits slippage. This can reduce the speed of
the coolant pump, alternator, and belt-driven fan. As a
result, the engine may overheat or the battery may become
discharged. An excessively loose belt will have a tendency
to whip or flap, which can cut hoses or cause intermittent
loading of the bearings in the coolant pump.
Direct Air Cooling
Direct air cooling is a method of directly transferring
engine heat to the surrounding air. It uses a fan to force air
around the cylinders and cylinder heads, which are the hottest parts of the engine. The fan is driven by the crankshaft
via a belt. The cylinders and heads of an air cooled engine
are made with fins to present a larger heat transfer surface.
The engine is surrounded by a sheet metal shroud to direct
more air over the hottest engine parts. Air-cooled engines
are no longer used on cars and light trucks.
85
Lubrication System
The lubrication system circulates engine oil to internal
engine parts. Engine oil serves several purposes. It must be
delivered to the right place at the right time and in the proper
quantity. The lubrication system may have no apparent effect
on driveability, but it is a vital part of the engine and some
defects in it can result in driveability symptoms. Also, some
driveability problems can affect the lubrication system.
The various moving parts of the engine are subjected
to differing levels of stress. The amount of oil needed varies between engine parts. Some parts of the engine are
lubricated by pressurized oil, while others are lubricated by
splashing oil. Figure 5-23 shows a typical pressure/splash
lubrication system.
The camshaft and crankshaft bearings are pressure lubricated. Also, hydraulic lifters must have a supply of pressurized
oil to work properly. On some engines, pressurized oil drips
through nozzles onto moving parts such as timing gears.
Some engine parts can be lubricated by oil that is
splashed onto them. Oil is thrown upward by the rotation of
the crankshaft. This oil strikes the engine cylinder walls, piston skirts, and piston pins. Some splashed oil also reaches
the camshaft and lubricates the cam lobes and valve lifters.
Engine Oil
The engine oil, often called motor oil, provides lubrication between moving parts. Oil is made to do a good job of
lubrication, sealing, cooling, shock absorption, and cleaning. It is also formulated to prevent sludge formation.
Coolant pump
Serpentine belt
Crankshaft
Starter / generator
Hydraulic belt tensioner
A/C compressor
Figure 5-22. Engines use one or two serpentine belts to drive all of the accessories. On this hybrid vehicle, a starter/generator is used
to restart the engine by driving the belt to turn the crankshaft. (Daimler)
86
Auto Engine Performance and Driveability
Head-cylinder
Engine variable
camshaft timing asy
Fundamentals of Engine Construction and Operation
Housing asyengine variable
timing LH
Tensionerengine timing
chain LH
87
Bottom of engine block
SM
Housing asyengine variable timing
Chapter 5
A
Tensionerengine
timing chain
Advance side
of variable
camshaft
timing
Block asycylinder
Valve
body asy
Filter
Retard side
of variable
camshaft
timing
Metering
orifice
To chain
tensioner
Oil pump
Housing asyengine variable timing
Adapter asyoil filter
Pump asyoil less screen
& cover
From head
Back to
head
Oil pumpscreen & cover asy
Camshaft
sprocket
bolt
B
Oil pan
–
–
From head
Triggerwheel
Oil filter
Oil to front
of camshaft
timing
Oil to rear
of camshaft
timing rotor
Engine
variable
camshaft
timing asy
Variable camshaft timing
auxiliary view
Oil pan asy
Variable timing asy RH
auxiliary view
Figure 5-23. Automotive engines use a combination of pressurized and splashed oil to lubricate engine components. The lubrication
system also serves to cool the internal engine components. Note that this engine also uses oil pressure to control a variable timing
system. (Ford)
Lubrication is the most obvious job of engine oil.
Oil reduces friction by forming a layer between moving
parts. All engine parts, no matter how finely machined,
have microscopic high spots. As one part moves across
another, these spots will contact each other. As a result,
the parts begin to wear and overheat from friction. The
oil separates the moving parts, preventing the high spots
from touching. The oil acts like a set of microscopic ball
bearings, allowing the parts to slide against each other.
Friction is greatly reduced.
Cooling is one of the less obvious jobs of engine
oil. It is difficult to remove heat from the piston heads.
They cannot be cooled by the cooling system, yet the
pistons are among the hottest parts in the engine. They
will overheat and melt if the heat is not removed. Even
a slightly overheated piston can develop a localized hot
spot that will cause detonation. Oil splashed under the
piston head absorbs heat from the piston. Oil splash also
removes heat from the cylinder walls, rods, crankshaft,
and other engine parts that cannot be directly cooled by
the engine cooling system. The oil itself is cooled by the
cooling system and by direct heat transfer when it is in
the oil pan.
–
–
Sealing is another task of engine oil. A thin film of oil
between the piston rings and cylinder wall seals in pressure.
If this oil is not present, pressure leakage (loss of compression) will prevent the engine from running.
For some moving parts, such as connecting rod journals
and rod bearings, engine oil provides shock absorption. The
oil cushions the shock when the rod changes direction at
high speeds. This extends bearing life and prevents engine
knocking. Other moving parts, such as the piston skirts and
cam lobes, are also cushioned by oil.
Cleaning is also an important job of engine oil. Engines
constantly collect impurities. Unburned gasoline, carbon
from the combustion process, and water vapor get into the
crankcase. These impurities can form sludge and varnish
deposits in an engine. The deposits can cause the engine
to overheat, burn oil, and prematurely wear out. Engine
oil contains detergents that prevent formation of sludge
by picking up impurities and holding them in suspension.
When the oil circulates through the oil filter, the impurities
are trapped.
The American Petroleum Institute (API) classifies oil
according to various factors that affect oil’s ability to prevent
friction and deposits in an engine. The API service classification is printed on the oil container, Figure 5-24. The API
Figure 5-24. A—Oil containers carry an American Petroleum
Institute (API) marking indicating the oil viscosity and classification. B—Oil temperature range chart.
Figure 5-25. The oil pan serves as the reservoir for the engine
oil as well as providing a surface for heat dissipation. Most
engines have a pan with a single sump. However, some engines
use either a dual- or dry-sump pan. (BMW)
Oil Pickup Screen
service classification is SM for most gasoline engines and
CH4 for most diesel engines. Oils with other classifications
are only for use in older engines. However, older engines
can use engine oil with the newest classification.
In addition to the API grades, the International
Lubricants Standardization and Approval Committee
(ILSAC), made up of American and Japanese vehicle manufacturers, classifies oils according to manufacturer test
criteria. Classifications are called GF for gasoline fueled. At
the present time, GF-4 is the latest standard.
Oil Pan
Oil that drips or is squirted out of any part of the lubrication system eventually drains into the oil pan. The oil pan
is a reservoir for engine oil and helps the oil to lose the heat
that it picked up in the engine. The air passing underneath
the vehicle removes this heat from the oil pan, Figure 5-25.
Most oil pans have a drain plug at the lowest point of the
pan. Some models have two drain plugs.
The oil pan is made of stamped sheet steel or cast aluminum. Aluminum pans may have cooling fins cast into the
bottom. The cast pan also adds some rigidity to the engine
block.
Some manufacturers are implementing a dry-sump
oiling system. In a dry-sump system, oil that reaches the
bottom of the pan is immediately pumped to a separate oil
reservoir. This leaves very little oil in the pan. The advantage of this system is that it allows the engine to be set
lower, which allows a lower hood profile. Dry-sump oiling
is a proven system that has been used for many years in
auto racing and motorcycles.
The oil pickup screen prevents any large particles,
such as dirt, sand, or metal shavings, from being circulated
in the lubrication system. The oil screen is installed on the
intake side of the oil pump, Figure 5-26. It is always located
at the lowest point in the oil pan. In this way, the screen is
always covered by oil. This keeps the oil pump from drawing in air if the oil level drops because of oil consumption
or sloshing during turns or hard braking.
Since it traps only large particles, the oil screen usually
does not become plugged until the engine reaches very high
mileage. Most oil screens cannot be removed and cleaned
unless the oil pan is removed.
Intake
Oil
pump
Bolt
Oil pickup screen
Figure 5-26. The oil pickup screen is either bolted or pressed
onto the oil pump. The pickup reaches into the bottom of the oil
pan sump to draw oil into the engine. (Chrysler)
88
Auto Engine Performance and Driveability
Chapter 5
Fundamentals of Engine Construction and Operation
Oil Pump
The engine oil pump develops oil pressure and flow
to circulate oil throughout the lubrication system. Usually,
it is driven by a gear on the camshaft or crankshaft. Most
gear-driven oil pumps are mounted near the bottom of the
engine and connect to the camshaft drive gear through
a shaft. Some oil pumps are installed in the engine front
cover and are directly driven by the engine crankshaft. The
oil pump speed varies with engine speed, since the pump
is driven by the engine.
Engine oil pumps are always constant-displacement
types. A constant-displacement pump delivers the same
amount of oil with each revolution. The faster the pump
revolves, the more oil it delivers. Figure 5-27 illustrates the
external-gear and rotor designs of oil pump. The externalgear design is most common; however, more and more
engines are equipped with rotor pumps.
When the pump gears rotate, the gear teeth unmesh in
the inlet area. This creates a low-pressure area that draws
oil from the oil pan or oil tank. The oil is carried around
the housing in the spaces between the gears and housing.
When the gear teeth mesh at the outlet, a high-pressure
area is created. The oil is squeezed out of the discharge
port. The process is then repeated.
Pressure Regulator
The oil pump has enough capacity to deliver sufficient
oil pressure and flow at idle speeds. At higher engine speeds,
the pump will produce too much oil pressure and flow.
This may rupture seals or filter elements, affect hydraulic
lifter operation, or cause oil burning.
Oil pump output is controlled by a pressure regulator.
The pressure regulator consists of a valve that is held closed
by a spring, Figure 5-28. Oil pressure from the pump pushes
against the valve on the opposite side from the spring. When
the oil pressure reaches a certain point, the spring is compressed and the valve opens. This dumps excess oil into the
sump, which is at a lower (near atmospheric) pressure. As a
Outlet
External gear
Inlet
Gear
Inlet
Outlet
Gear
External gear pump
Internal
Rotor pump gear
Figure 5-27. The oil pump may be of the external gear or rotor
design. Both designs have a positive displacement.
Seat
Ball
Spring holding the ball
against the seat
Normal
oil
pressure
Oil pressure acting on the ball
compresses the spring
Figure 5-29. Oil filters come in many sizes and shapes. While it
is a very simple and inexpensive part, the filter is very important
to good engine performance.
elsewhere in the engine compartment. Some oil filters are
installed in the oil pan or an engine-mounted canister and
do not have housings.
High oil
pressure
Oil Galleries
Oil flows to the pan
Figure 5-28. The pressure regulator controls the maximum
oil pressure. Normal oil pressure will not unseat the valve.
However, high oil pressure forces the valve open, allowing oil
to flow to the pan.
Oil galleries are internal engine passages that carry
the oil. They are cast or drilled into the engine block and
heads. Galleries extend from the pump and filter to the
crankshaft and camshaft bearings, valve lifters, and rocker
arm shafts. Galleries are drilled in the crankshaft to allow
oil to reach the connecting rod bearings. Removable plugs
are located at the rear of some engine blocks to allow the
galleries to be cleaned during an overhaul.
Gaskets, Seals, and Sealant
result, the oil pressure is regulated. Engine oil pressure is usually regulated to about 35–45 psi (240–310 kPa). Minimum
pressure at idle should be 15–20 psi (105–140 kPa).
Oil Filter
The oil filter removes small particles and contaminants from the engine oil. It consists of a stamped metal
housing containing, typically, a pleated paper filter element. Other types of elements may be used. The filter is
always installed on the outlet side of the oil pump. Oil
under pressure flows into the filter, through the filter element, and out of the filter.
The oil filter contains an internal bypass. This allows
oil to flow past the filter if the element becomes clogged.
However, the oil is not filtered when this happens. Some
oil filters have an anti-drainback valve. This valve closes to
keep oil from draining out of the filter when the engine is
not operated for long periods.
The oil filter is replaced during an oil change as part
of normal engine maintenance. A typical oil filter, such as
the ones shown in Figure 5-29, can be removed from the
engine by unscrewing it from the mounting pad. In some
engine designs, the oil filter is mounted on the firewall or
Gaskets and seals are used in the intake system to seal
air and fuel in and to prevent vacuum leaks. Preventing
fuel and air leaks is vital to driveability, performance, and
emissions. Gaskets and seals must stand up to high engine
temperatures, but be pliable enough at various operating
temperatures to create the intended seal.
Summary
The four-stroke cycle operates through two revolutions of the crankshaft. The intake stroke draws air and fuel
into the cylinder. The compression stroke compresses the
air-fuel mixture. When the mixture ignites, it pushes the
piston down for the power stroke. On the exhaust stroke,
the upward movement of the piston pushes the exhaust
gases out of the cylinder. The cycle then repeats.
The major components of a reciprocating-piston
engine are the engine block, pistons and rings, connecting
rods, crankshaft, cylinder head(s), valves, and valve train.
The valves are driven by the crankshaft through a set of
gears, a gear and chain arrangement, or sprockets and a
89
drive belt. On some engines, valve operation is controlled
by a mechanism operated by a computer.
The cooling system removes unwanted engine heat
and regulates engine temperature. Cars and light trucks
have a liquid cooling system. Coolant is pumped through
engine passages by a belt-driven pump. A radiator removes
heat from the coolant. Engine coolant is a mixture of antifreeze and water. Antifreeze may be ethylene glycol or
propylene glycol.
Poor lubrication can eventually result in driveability
symptoms. The lubrication system circulates engine oil to
internal engine parts. Oil galleries are internal passages that
carry the oil throughout the engine. The oil pump is driven
by a gear on the camshaft or by the engine timing belt. A
pressure regulator controls oil pump output. The engine oil
provides lubrication, reduces friction, helps with cooling,
seals, provides shock absorption between parts, and cleans
parts. It is formulated to prevent sludge formation.
Review Questions—Chapter 5
Please do not write in this text. Write your answers on
a separate sheet of paper.
1. Name the four strokes in a four-stroke cycle engine.
2. List the major parts installed on or in the engine
block.
3. The ______ transfer the force of the expanding
combustion gases to the connecting rods.
4. A film of ______ between the compression rings and
cylinder wall seals pressure in the cylinder.
(A) carbon
(B) oil
(C) unburned fuel
(D) None of the above.
5. The _____ converts the straight-line motion of the
piston into rotary motion.
(A) piston
(B) crankshaft
(C) flywheel
(D) connecting rod
6. What holds intake and exhaust valves closed?
(A) The camshaft.
(B) Compression pressure.
(C) Valve spring pressure.
(D) Expanding combustion gases.
90
7. The camshaft turns at _____ the speed of the
crankshaft.
(A) about half
(B) exactly half
(C) about twice
(D) exactly twice
8. _____ and ____ are the two general types of variable
valve timing.
9. List two devices used to reduce engine vibration.
10. Cars and light trucks manufactured today are _____
cooled.
(A) air
(B) liquid
(C) oil
(D) thermostatically
11. The purpose of antifreeze is to:
(A) reduce rust and corrosion in the engine and
radiator.
(B) lower the freezing point of the engine coolant.
(C) increase the boiling point of the engine coolant.
(D) All of the above.
12. By pressurizing the cooling system, the boiling point
of the engine coolant is _____.
13. Engine oil is used to ______ various parts of the
engine.
(A) cool
(B) lubricate
(C) cushion
(D) All of the above.
14. Engines are usually lubricated by:
(A) pressurized oil.
(B) splashed oil.
(C) a combination of pressurized/splashed oil.
(D) None of the above.
15. Engine oil pressure is controlled by a pressure
regulator, typically in the range of:
(A) 5–15 psi (35–105 kPa)
(B) 15–20 psi (105–140 kPa)
(C) 20–35 psi (140–240 kPa)
(D) 35–45 psi (240–310 kPa)
Auto Engine Performance and Driveability
ASE Certification-Type Questions
1. Technician A says that an engine must have sufficient
compression before it will start and run. Technician B
says that compression is developed on the power
stroke of a four-cycle engine. Who is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
2. All of the following statements about oil control rings
are true, except:
(A) oil control rings are installed below the
compression rings.
(B) there should be no oil at the compression rings.
(C) oil control rings scrape oil from the cylinder
walls when the piston is moving down.
(D) defective oil control rings will cause high oil
consumption
3. Technician A says that the intake valves are cooled
by incoming air. Technician B says that the intake
valve must be in contact with its seat long enough to
transfer heat to the cylinder head. Who is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
4. Cylinder heads contain all of the following, except:
(A) intake valves.
(B) exhaust valves.
(C) EGR valves.
(D) camshafts.
5. The valve train is the group of components that opens
the ______.
(A) intake valves
(B) exhaust valves
(C) EGR valve
(D) Both A & B.
6. A hydraulic lash adjuster, similar in operation to a
hydraulic lifter, maintains the proper valve clearance
on ______ engines.
(A) cam-in-block
(B) roller-lifter
(C) overhead cam
(D) All of the above.
Chapter 5
Fundamentals of Engine Construction and Operation
7. Technician A says that overhead camshafts are
usually driven by a belt. Technician B says that in
cam-in-block, overhead valve engines, the camshaft
is usually directly driven by two meshing gears. Who
is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
8. Most vehicle manufacturers recommend a ______
mix of water and antifreeze.
(A) 10:90
(B) 50:50
(C) 30:70
(D) 80:20
9. Oil screens on the inlet to the oil pump are to
remove:
(A) large particles of dirt or metal.
(B) small particles of dirt or metal.
(C) chemical contaminants.
(D) particles the oil filter does not catch.
10. Technician A says that engine oil pumps are
constant-displacement pumps. Technician B says
that the engine oil pan serves as the reservoir for
engine oil. Who is correct?
(A) A only.
(B) B only.
(C) Both A & B.
(D) Neither A nor B.
91
92
Auto Engine Performance and Driveability
Electricity is used throughout the vehicle. Some vehicles use electricity to assist the gasoline or diesel engine in moving the vehicle.
In other vehicles, such as this car from Smart, only electricity propels the vehicle. (Daimler)