PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 2/TASK 3
(1) Liquid. Liquid is the most popular coolant in automotive use. A liquid
cooling system provides the most positive cooling and is best for maintaining an
(2) Air. Air cooling is most practical for small vehicles and equipment because
no radiator or hoses are required. Air cooling generally will not be used wherever
water cooling is practical. This is because aircooled engines do not run at even
temperatures and require extensive use of aluminum to dissipate heat.
b. Other Sources of Engine Cooling. There are other sources of heat dissipation
(1) The exhaust system dissipates as such, if not more, heat than the cooling
system, although that is not its purpose.
(2) The engine oil, as stated in paragraph 1 on page 58, removes heat from the
engine and dissipates it to the air from the sump.
(3) The fuel provides some engine cooling through vaporization.
(4) A measurable amount of heat is dissipated to the air through radiation from
a. Flow of Coolant (figure 64 on the following page). A simple liquidcooled
cooling system consists of a radiator, coolant pump, piping, fan, thermostat, and a
system of jackets and passages in the cylinder head and cylinder block through
which the coolant circulates. Some engines are equipped with a water distribution
tube inside the cooling passages; these direct additional coolant to the points
where the temperatures are highest. Cooling of the engine parts is accomplished by
keeping the coolant circulating and in contact with the metal surfaces to be
cooled. The pump draws the coolant from the bottom of the radiator, forces it
through the jackets and passages, and ejects it into the upper tank on the top of
the radiator. The coolant then passes through a set of tubes to the bottom of the
radiator from which the cooling cycle begins again. The radiator is situated in
front of a fan driven either by the water pump or by an electric