Service Manual

Sea Water System Diagnostics ISB, ISBe and QSB (Common Rail [...]
Page 8-118 Section 8 - Cooling System - Group 08
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If the pressure drop across the heat exchanger is within
specification, determine the pressure drop across the
exhaust elbow (diffuser). This is done by subtracting the
heat exchanger outlet pressure form the sea water pump
outlet pressure. If this pressure exceeds the maximum
specification, check for blockage in the exhaust elbow
(diffuser) and exhaust system of the vessel. Clean or
replace if necessary.
Refer to Procedure 018-018 for Marine engine
specifications.
Some vessels are equipped with a sea water bypass
valve to divert sea water flow from the exhaust elbow. If
the valve is adjusted to the lowest system pressure, be
sure the exhaust piping does not overheat under all
operating conditions.
Temperature Differential Test
Fabricate a sea water test tool by using a 38 mm [1-1/2 in]
pipe with a fitting in the center to connect a temperature
probe.
Install the sea water test tool with a temperature probe
between the outlet side of the heat exchanger and the
exhaust elbow (1). Operate the engine at rated rpm and
load and record the temperature.
Install the temperature probe in the outlet side of the
aftercooler (1). Operate the engine at the rated rpm and
load and record the temperature. If the temperature
difference between the aftercooler outlet and the engine
heat exchanger outlet is greater than 20°C [40°F], check
the sea water pump for water flow problems. Refer to
Procedure 008-057