Mie (Inboard) Engines; Exhaust Hose Connection - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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SERVICE MANUAL NUMBER 23

MIE (Inboard) Engines

When designing and installing exhaust system, it is very important that the following addi-

tional points be taken into consideration:

1. System layout and construction must prevent cooling system discharge water from flow-

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 mini-

4. Exhaust outlet must be slightly above the waterline with boat at rest in the water and full

5. System must not cause excessive back pressure. Back pressure MUST NOT exceed

454 Mag 8.2L

1. Exhaust hoses must be connected to exhaust elbows so that they do not restrict the flow

2. Exhaust hoses must be secured at each connection with two hose clamps.

90-861326--1 MARCH 1999

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ing back into engine and also must prevent seawater from entering engine via exhaust

at any point.

mum 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 minimum drop of 4 in.

(102 mm) overall. (This is an American Boat & Yacht Council recommendation.) The

drop must be constant so that a low spot does not exist at any point in the exhaust hose

load aboard. Exhaust outlet should be equipped with an internal shutter to prevent sea-

water from running back into exhaust system. The use of an exhaust flapper on each

outlet also is recommended.

4 in. (102 mm) of mercury when measured with a mercury manometer at exhaust elbow

outlets. Minimum exhaust hose sizes are given in chart.

Minimum Hose Size Inside Diameter (I.D.)

of discharge water from the elbow. If hoses are connected incorrectly, a hot spot in the

hose can occur, and can eventually burn through.

Single Outlet

5 in. (127 mm)

4 in. (102 mm)

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