Page 194 - REPOWER REFERENCE GUIDE (2020)

Exhaust System Installation Requirements—Sterndrive Applications
Exhaust System Design

Important Information

NOTICE
Improperly designing, installing, or modifying the engine’s exhaust system can introduce seawater or water from
condensation into the combustion chambers, damaging the engine. The installing dealer or boatbuilder is responsible for
proper installation of the exhaust system as explained in the installation instructions for the product. Engine damage resulting
from water ingestion is not covered by the product warranty, unless the damage is the result of a defective part supplied by
the engine manufacturer.

The exhaust system must be installed in accordance with the information contained in this section to prevent water intrusion
problems. Special care is required on the transom or hull exhaust applications, as these custom‑designed exhaust systems can
create a tuning effect that can cause water to be forced back into the engine. Checking for water intrusion must be performed to
ensure that water intrusion is not occurring. It is the boat manufacturer's responsibility for ensuring that water intrusion does not
exist with their unique exhaust system.
Engines with through‑the‑propeller exhaust have been carefully designed and tested to avoid water intrusion problems and no
additional testing is required. These applications require that only that exhaust elbow height be checked as outlined under
Measuring Exhaust Elbow Height section.

! WARNING
Installing the exhaust system incorrectly can lead to serious injury or death. When installing or designing exhaust systems,
follow all federal, state, and local boating and safety standards for the market in which the boat will be sold.
Exhaust system design and installation can affect:
• Noise level.
• Performance.
• Water Intrusion.
• Carbon monoxide levels.
• Component longevity.
Preferred Exhaust System

Most Mercury MerCruiser sterndrive engines were developed and tested for Y‑pipe or through the propeller exhaust systems.
By using the Y‑pipe system, you limit the potential for water intrusion due to the exhaust system design. The only exception to
this is the 496 MAG engine. 496 MAG models are set up from the factory for through‑the‑transom hull exhaust to provide the
optimum performance output.
Exhaust Connections
NOTICE

Hot spots in exhaust hoses can damage hoses and cause leaks. Ensure that discharge water from the exhaust elbow flows
without restriction through all hoses and fittings.

Exhaust hoses must be properly installed on exhaust elbow outlets. Discharge water from the exhaust elbow must flow around
the entire inside diameter of hose to avoid causing hot spots that could burn through the hose.

18576 18577
Correct Incorrect

Page 7C-2 © 2019 Mercury Marine 90-8M0149179 eng NOVEMBER 2018