PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 2/TASK 3
b. Engine Water Jackets (figure 64 on the previous page). The water passages in
the cylinder block and cylinder head form the engine water jacket. In the majority
of cylinder blocks, the water jacket completely surrounds all cylinders along their
full length. Within the jacket, narrow passages are provided between cylinders for
coolant circulation. In some engine configurations, however, the cylinder bores
are attached to each other and a coolant passageway is not provided between bores.
An engine of this design often is referred to as having siamese cylinders. This
type of engine tends to operate with cylinder temperatures slightly higher between
the bores, and slightly cooler where water jackets come in contact with the bores.
In addition, all engines are provided with water passages around the exhaust valve
seat. This provides cooling for the valve when it comes in contact with the seat.
the cylinders and contains water passages around the valve seats when these are
located in the head. The coolant flows from the cylinder block up into the
cylinder head through passages called water transfer ports. A tight seal at the
ports between the cylinder head and block is very important. The watertight seal
at the ports, as well as the gastight seal at the combustionchamber openings, is
obtained with one large gasket called the cylinderhead gasket.
c. Coolants. Water is by far the most popular coolant for liquidcooled engines.
It is plentiful, inexpensive, and its boiling point is within the efficient
operational temperature range of the engine.
(1) Antifreeze Protection. When a vehicle is operated in areas where the
temperature falls below 32 F (0 C), an antifreeze solution must be added if water
is used as the coolant. The most common antifreeze is ethylene glycol. Other
antifreezes that are little used are glycerin, methyl alcohol, and ethyl alcohol.
Ethyl and methyl alcohol provide adequate protection as an antifreeze when used in
sufficient quantities. The main objection to these liquids, however, is that they
evaporate below the operating temperature of modern automotive engines, making them
impractical. Glycerin offers the same degree of protection as alcohol, but does
not evaporate in use, has a high