6B - 4 - CLOSED COOLING MODELS
90-816462 2-695
a. Start engine. Re-pressurize system to pre-
viously specified amount and observe pres-
sure gauge on tester. If needle in gauge vi-
brates, compression or combustion is leaking
into closed cooling section from a leak in the
combustion chamber. Exact cylinders, where
leakage is taking place, sometimes can be
found by removing spark plug wires (one at a
time) while observing pressure gauge. Vibra-
tion will decrease or stop when plug wire is re-
moved from leaking cylinder. Stop engine.
b. Remove spark plugs (one at a time) from cyl-
inders and examine for presence of coolant.
A spark plug that is perfectly clean or milky ap-
pearing is a sure indication of a leak.
c. Drain oil from engine and examine for pres-
ence of coolant. Oil usually will be milky if
coolant is present. If coolant is present, re-
move engine from boat and drop the oil pan.
With engine in the upright position, re-pres-
surize closed cooling section to previously
specified amount and examine internal sur-
faces of engine to locate leak.
d. If no leakage can be found in above steps, en-
tire engine must be disassembled and in-
spected for leakage.
Testing for Cylinder Head Gasket
Leak
A leaking head gasket will cause combustion gas to
be forced into the cooling system. The mixture of
coolant and tiny air bubbles is a poor heat conductor
and will overheat an engine quickly. Compression
tests or cooling system pressure check normally will
not detect the leak because the test pressure is far
below the combustion pressures which cause the
leak. An effective test is as follows:
IMPORTANT: Run boat in lake for this test. It is
best to run the engine at or above cruising speed
during this test. Usually a failed head gasket will
not cause the engine to overheat below cruising
speed.
1. Install a clear plastic hose between the reservoir
and coolant recovery bottle. Use a 2-3 ft. (61-91
cm) long hose for this test.
2. Route this hose so a “U” is formed.
3. Put enough coolant into hose to fill the center 4 or
5 inches (10-13 cm) of the “U.”
4. Observe the “U” while the engine is running.
a. During Idle and Warm-Up: Some coolant
and/or air will leave the reservoir.
b. During Cruising Speed (2500-3500 RPM):
Coolant and/or air leaving the reservoir
should stop after approximately five minutes
running at a given RPM. A leaking head gas-
ket will produce air bubbling through the “U,”
going to the coolant recovery bottle. The fre-
quency and size of the bubbles will depend on
the size of the leak.
c. At Higher Speeds (4000+ RPM): Normal op-
eration is the same as described in “b” above.
A failed head gasket will cause the bubbles to
come faster and may be accompanied by vio-
lent, intermittent bursts of coolant.
It is important not to confuse normal warm-up expan-
sion with a failed head gasket. Normal warm-up pro-
duces an intermittent flow of coolant which will stop
within approximately five minutes at a given RPM. A
head gasket leak will not stop because the one thing
that marks a failed head gasket is the continued pas-
sage of air. This may be accompanied by violent, in-
termittent bursts of coolant leaving the reservoir. If
coolant continues to flow (not in violent, intermittent
bursts) from the reservoir at cruising speed, some-
thing else besides the head gasket is causing the en-
gine to overheat.
Testing Heat Exchanger
FOR INTERNAL LEAK: An internal leak will cause
coolant to go into the seawater circuit when pressure
is put on the closed cooling circuit.
1. Remove a seawater hose from the exchanger. Do
not drain the exchanger.
2. Pressurize the closed cooling circuit to 14-20 PSI
(97-138 kPa) with a radiator tester.
3. If seawater begins to flow from the nipple there is
a leak.
FOR BLOCKAGE:
IMPORTANT: Seawater flows THROUGH the
tubes in the exchanger. Closed cooling coolant
flows AROUND the tubes.
1. Remove end caps and inspect for any blockage
in the seawater circuit (broken impeller blades,
weeds, etc.).
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Страница 7: ...1 A IMPORTANT INFORMATION GENERAL INFORMATION 72000 ...
Страница 15: ...1 B 50617 IMPORTANT INFORMATION MAINTENANCE ...
Страница 36: ...1 C IMPORTANT INFORMATION TROUBLESHOOTING ...
Страница 74: ...2 A 50633 REMOVAL AND INSTALLATION 4 CYL ALPHA ONE DRIVE ...
Страница 88: ...3 A 26790 ENGINE 181 CID 3 0L 4 CYLINDER GM ENGINE ...
Страница 137: ...4 A 72079 ELECTRICAL SYSTEMS STARTING SYSTEM ...
Страница 170: ...4 B 71855 ELECTRICAL SYSTEMS IGNITION SYSTEM ...
Страница 197: ...ELECTRICAL SYSTEMS CHARGING SYSTEM 4 C 72078 ...
Страница 237: ...4 D 72747 ELECTRICAL SYSTEMS INSTRUMENTATION ...
Страница 250: ...4 E 72938 ELECTRICAL SYSTEMS WIRING DIAGRAMS ...
Страница 264: ...5 A FUEL SYSTEM FUEL PUMP ...
Страница 271: ...5 B 72681 FUEL SYSTEM MERCARB 2 BARREL CARBURETOR ...
Страница 300: ...6 A 50628 COOLING SYSTEM SEAWATER COOLED MODELS ...
Страница 309: ...6 B 73665 COOLING SYSTEM CLOSED COOLING MODELS ...
Страница 325: ...C 6 EXHAUST SYSTEM MANIFOLD ...
Страница 331: ...7 A 71317 POWER STEERING PUMP ...