Mercury MerCruiser D2.8L D-Tronic Service Manual page 741

SERVICE MANUAL NUMBER 22
5. Attach an automotive-type cooling system pressure tester to filler neck and pressurize
closed cooling system to amount specified in following chart, based on pressure cap
rating for your engine.
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 system, visually inspect
external portion of cooling system (hoses, gaskets, drain plugs, core plugs, circulating
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:
•
Loose cylinder head bolts or damaged gasket
•
Loose turbocharger bolts or damaged gasket
•
Loose exhaust elbow or damaged gasket
•
Cracked or porous cylinder head or block
•
Cracked or porous exhaust manifold
10. Proceed as follows until location of internal leak is found:
a. Start engine. Pressurize system to previously specified amount and observe
b. Remove glow plugs (one at a time) from cylinders and examine for presence of
c. Drain oil from engine and examine for presence of coolant. Oil usually will be milky
d. If coolant is present, remove engine from boat and remove the oil pan. With engine
e. If no leaks can be found in above steps, entire engine must be disassembled and
90-860074-1 FEBRUARY 2002
Pressure Cap Rating
97 kPa (14 psi)
pressure gauge on tester. If needle in gauge vibrates, compression or combustion
is leaking into closed cooled section from a leak in the combustion chamber. Stop
engine.
coolant. A glow plug that is perfectly clean or milky appearing is a sure indication of
a leak.
if coolant is present.
in the upright position, pressurize closed cooled section to previously specified
amount and examine internal surfaces of engine to locate leak.
inspected for leaks.
CLOSED COOLING SYSTEM
Amount of Pressure
Applied to Closed
Cooling System
137 kPa (20 psi)
Page 6B-13