Service manual

CLOSED COOLED MODELS SERVICE MANUAL NUMBER 26
Page 6B-6 90-861329--1 MARCH 1999
5. Attach an automotive-type cooling system pressure tester to filler neck and pressurize
closed cooling section to amount specified in following chart, based on pressure cap rat-
ing for your engine.
Pressure Cap Rating
Amount of Pressure
Applied to Closed
Cooling System
14 psi (97 kPa) 17 psi (117 kPa)
6. Observe gauge reading for approximately two minutes; pressure should not drop during
this time. If pressure drops, proceed with the following steps until leakage is found.
7. While maintaining specified pressure on closed cooling section, visually inspect exter-
nal portion of cooling system (hoses, gaskets, drain plugs, petcocks, core plugs, circu-
lating pump seal, etc.) for leakage. Also listen closely for bubbling or hissing, as they
usually are a sure indication of a leak.
8. Refer to “Testing Heat Exchanger” in this section and test as outlined.
9. If no leakage could be found in above steps, engine is leaking internally, and it probably
is due to one or more of the following: (1) loose cylinder head bolts or damaged gasket,
(2) loose intake manifold bolts or damaged gasket, (3) loose exhaust elbow or distribu-
tion block retaining nuts or damaged gasket, (4) cracked or porous cylinder head or
block, or (5) cracked or porous exhaust manifold. Proceed as follows until location of
internal leak is found.
a. Start engine. Re-pressurize system to previously specified amount and observe
pressure gauge on tester. If needle in gauge vibrates, 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. Vibration will
decrease or stop when plug wire is removed from leaking cylinder. Stop engine.
b. Remove spark plugs (one at a time) from cylinders and examine for presence of
coolant. A spark plug that is perfectly clean or milky appearing is a sure indication
of a leak.
c. Drain oil from engine and examine for presence of coolant. Oil usually will be milky
if coolant is present. If coolant is present, remove engine from boat and drop the oil
pan. With engine in the upright position, re-pressurize closed cooling section to pre-
viously specified amount and examine internal surfaces of engine to locate leak.
d. If no leakage can be found in above steps, entire engine must be disassembled and
inspected 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.
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