Mie (Inboard) Engines; Exhaust Hose Connection - Mercury 305 CID Service Manual

MIE (Inboard) Engines

When designing and installing exhaust system, it is
very important that the following additional points be
taken into consideration:
1. System layout and construction must prevent
cooling system discharge water from flowing
back into engine and also must prevent seawater
from entering engine via exhaust at any point.
2. The exhaust hoses and pipes must not be higher
than exhaust elbows at any point.
3. The exhaust outlet (for routing exhaust to outside
of boat) must be located so that a minimum of 1/2
in. (13 mm) per foot (305 mm) downward pitch
(drop) exists in the exhaust hose or pipe from the
engine exhaust elbow to the outlet, with a mini-
mum drop of 4 in. (102 mm) overall. (This is an
American Boat & Yacht Council recommenda-
tion.) The drop must be constant so that a low
spot does not exist at any point in the exhaust
hose or pipe.
4. Exhaust outlet must be slightly above the water-
line with boat at rest in the water and full load
aboard. Exhaust outlet should be equipped with
an internal shutter to prevent seawater from run-
ning back into exhaust system. The use of an ex-
haust flapper on each outlet also is recom-
mended.
5. System must not cause excessive back pres-
sure. Back pressure MUST NOT exceed 4 in.
(102 mm) of mercury when measured with a mer-
cury manometer at exhaust elbow outlets. Mini-
mum exhaust hose sizes are given in chart.
Minimum Hose Size
Model Single Outlet
All (Except
5 in. (127 mm)
Magnums)
Index
7A-2 - GENERAL

Exhaust Hose Connection

1. Exhaust hoses must be connected to exhaust el-
a - Correct Connection
b - Incorrect Connection
2. Exhaust hoses must be secured at each connec-
Dual Outlet
4 in. (102 mm)
bows so that they do not restrict the flow of dis-
charge water from the elbow. If hoses are con-
nected incorrectly, a hot spot in the hose can
occur, and can eventually burn through.
a
b
tion with two hose clamps.
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