radiator. The coolant collects heat from the hot engine
parts and carries it back to the radiator.
The radiator allows the coolant heat to transfer into
the outside air. An engine fan draws cool air through the
radiator. The thermostat controls coolant flow and engine
temperature. It is usually located where the top radiator
hose connects to the engine.
The lubrication system reduces friction and wear
between internal engine parts by circulating filtered
engine oil to high-friction points in the engine. The lubri-
cation system also helps cool the engine by carrying heat
away from internal engine parts.
Study the parts and operation of the lubrication
system shown in Figure 1-16. Note how the oil pump
pulls oil out of the pan and pushes it to various moving
parts of the engine.
Exhaust and Emission Control Systems
The exhaust system quiets the noise produced during
engine operation and routes engine exhaust gases to the
rear of the vehicle body. Figure 1-17 illustrates the basic
parts of an exhaust system. Trace the flow of exhaust
gases from the engine exhaust manifold to the tailpipe.
Learn the names of the parts.
Various emission control systems are used to reduce
the amount of toxic (poisonous) substances produced by
an engine. Some systems prevent fuel vapors from
entering the atmosphere (air surrounding the earth).
Other emission control systems remove unburned and
partially burned fuel from the engine exhaust. Later chap-
ters cover these systems in detail.
Drive Train Systems
The drive train transfers turning force from the engine
crankshaft to the drive wheels. Drive train configurations
vary, depending on vehicle design. See Figure 1-18.
The drive train parts commonly found on a front-
engine, rear-wheel-drive vehicle include the clutch, trans-
mission, drive shaft, and rear axle assembly. The drive
train parts used on most front-engine, front-wheel-drive
vehicles include the clutch, transaxle, and drive axles.
Refer to Figure 1-18 as these components and assem-
blies are discussed.
Clutch
The clutch allows the driver to engage or disengage
the engine and manual transmission or transaxle. When
the clutch pedal is in the released position, the clutch
locks the engine flywheel and the transmission input
shaft together. This causes engine power to rotate the
transmission gears and other parts of the drive train to
propel the vehicle. When the driver presses the clutch
pedal, the clutch disengages power flow and the engine
no longer turns the transmission input shaft and gears.
Transmission
The transmission uses various gear combinations, or
ratios, to multiply engine speed and torque to accommo-
date driving conditions. Low gear ratios allow the vehicle
to accelerate quickly. High gear ratios permit lower
engine speed, providing good gas mileage.
A manual transmission lets the driver change
gear ratios to better accommodate driving conditions,
Figure 1-19. An automatic transmission, on the other
hand, does not have to be shifted by the driver. It uses an
internal hydraulic system and, in most cases, electronic
controls to shift gears. The input shaft of an automatic
transmission is connected to the engine crankshaft
through a torque converter (fluid coupling) instead of a
clutch. The elementary parts of an automatic transmis-
sion are pictured in Figure 1-20.
Drive Shaft
The drive shaft, or propeller shaft, transfers power
from the transmission to the rear axle assembly. Look at
Chapter 1 The Automobile 13
Figure 1-15. The cooling system must protect the engine from
the heat of combustion. Combustion heat could melt and ruin
engine parts. The system must also speed warm-up and main-
tain a constant operating temperature. Study the part names.
Hot coolant
Water
pump
Engine
water
jacket
Crankshaft
Fan belt
Cooled coolant
Airflow to
remove heat
from coolant
Fan
Radiator