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Section 4 Engine Service
is low on fl uid will not take a full charge. This
battery will eventually overheat the plates and
fail completely. Sulfated plates will cause bat-
tery failure also. Refer to the Batteries section in
Chapter 15 of this text for detailed information on
charging batteries.
Pressurized Liquid Cooling
System Service
The pressurized liquid cooling systems used
in small engines require maintenance similar to
that employed in the automobile engine. Because
the combination of water and metal sometimes
produces harmful chemical reactions that attack
the water jacket, antifreeze containing a chemical
rust inhibitor should be added whenever a sys-
tem is drained and refi lled. If rust and scale are
allowed to form and accumulate, the walls of the
water jacket will become insulated. This will cause
engine heat to be retained rather than removed.
Scale settling to the bottom may plug water
passages in the cylinder block and clog water tubes
in the radiator. Without free circulation of water,
the engine will run hot even when the thermostat
is open. Local hot spots can occur in the engine
when the passages in the block are obstructed.
In severe cases, water may boil inside the
block, and the steam will prevent water from
contacting and cooling inner walls. Then, serious
overheating and damage to parts of the engine
are bound to occur.
The cooling fi ns that surround the tubes of
the radiator should be kept clean for effi cient
heat transfer. Compressed air or pressurized
water will remove any accumulations that might
prevent air from passing through the fi ns and
across the tubes. To remove debris, direct the
fl ow of air or water in the opposite direction of
normal airfl ow.
Engine blocks and radiators may be cleaned
periodically by reverse fl ushing the system with
pressurized water. Disconnect the hoses from the
radiator and the block. Force clean water through
the block or the radiator in the direction opposite
that of normal circulation. This will push loose
sediment out. Continue fl ushing until the water
runs clear. Flushing should be done with the
engine stopped and cool. To remove additional
rust clinging to inner surfaces, use a commercial
cooling system rust remover. Follow the manufac-
turer’s instructions.
When adding coolant, mix water and anti-
freeze as specifi ed by the manufacturer. In most
cases, a mixture that contains 50% water and 50%
antifreeze is recommended. Never use just water.
The 50/50 mixture will prevent the coolant from
freezing in cold weather. It will also increase the
boiling point of the coolant.
Always check the strength of the coolant before
the cold season begins. Weak coolant can freeze,
causing damage to the engine block and radiator.
Coolant strength can be checked with a device
known as a coolant hydrometer. See Figure 13-23.
To use the hydrometer, simply place the pickup
tube in the engine coolant and squeeze the bulb to
draw coolant into the hydrometer. Most hydrome-
ters contain small balls that fl oat in the coolant. The
number of balls that fl oat indicates the strength of
the coolant. Some hydrometers have a pointer that
indicates coolant strength on a scale printed on the
body of the tester.
Maintaining Outboard Cooling
Systems
Outboard engine cooling systems can be
clogged with dirt, sand, or other debris. Flush-
ing the internal cooling system of an outboard
engine is extremely important. Flushing is done
by attaching a freshwater hose to the water scoop
or by operating the engine in a barrel of freshwater
for several minutes.
Figure 13-22.
After cleaning, rinse the battery, terminals, and cable
connectors with clear water.