82 Auto Engine Performance and Driveability
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 9–F (–13–C) and
water freezes at 32–F (0–C). When ethylene glycol and
water are mixed, however, the freezing point of the mix-
ture is lower than either liquid alone. A 50:50 mixture of
ethylene glycol and water freezes at about –35–F (–37–C).
A mixture of 2/3 ethylene glycol and 1/3 water freezes at
about –67–F (–55–C). A 50:50 mixture of propylene glycol
and water freezes at about –26–F (–32–C). 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 boil-
ing point than plain water. A 50:50 mixture boils at about
222–F (106–C). 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 deter-
mine whether a particular antifreeze is suitable for a par-
ticular 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 contain-
ing 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 hun-
dred 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 manufac-
ture. 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.
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 cool-
ant 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 trans-
mission 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 5-15. The coolant pump uses an impeller to move the
coolant through the engine. Coolant pumps are either belt- or
gear-driven.
Drive pulley
Housing
Inlet
(lower radiator
hose connection)
Impeller
Coolant is
thrown
outward
by the impeller