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TM 9-8000
Figure 9-1. Liquid Cooled System
the majority of cylinder blocks the water jacket
The coolant flows from the cylinder block up into the
completely surrounds all cylinders along their full length.
cylinder head through passages called water transfer
Within the Jacket, narrow passages are provided
ports. A tight seal at the ports between the cylinder head
between cylinders for coolant circulation. However, in
and block is very important. The watertight seal at the
some engine configurations the cylinder bores are
ports, as well as the gastight seal at the combustion-
attached to each other and a coolant passageway is not
chamber openings, is obtained with one large gasket
provided between bores. An engine of this design often
called the cylinder-head gasket.
is referred to as having siamese cylinders. This type of
engine tends to operate with cylinder temperatures
9.5. Coolants. Water is by far the most popular coolant
slightly higher between the bores, and cooler where
for liquid-cooled engines. It is plentiful, inexpensive, and
water Jackets come in contact with the bores.  In
its boiling point is within the efficient operational
addition, all engines are provided with water passages
temperature range of the engine.
around the exhaust valve seat. This provides cooling for
the valve when it comes in contact with the seat.
Antifreeze Protection.
When a vehicle is
operated in areas where the temperature falls below
b. In the cylinder head, the water jacket covers the
32F (0C), an antifreeze solution must be added if water
combustion chambers at the top of the cylinders and
is used as the coolant. The most common antifreeze is
contains water passages around the valve seats when
ethylene glycol. Other antifreezes that are little used are


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