Indmar 5.7L Vortec Operator's Manual page 61

Even with diligent flushing, certain exhaust system com-
ponents called exhaust risers or exhaust elbows will be
significantly affected by salt water. These risers must be
inspected by your dealer annually and replaced as
required. It is not unusual to have to replace these risers
every two years on boats used exclusively in salt water.
Fresh Water Cooling – Half Systems
A fresh water cooling system that uses anti-freeze in the
engine but raw water in the exhaust manifolds is referred
to as a half-system. This is the most common type of
system installed on water-ski boats. Although the engine
is protected, it is still important to flush the engine with
fresh water to remove as much salt water as possible
from the raw water side of the cooling system as well as
from the exhaust manifolds and risers. For more conven-
ient flushing, ask your dealer about permanently
installing a flushing device that allows easy connection of
a water hose.
Even with diligent flushing, certain cast iron exhaust sys-
tem components called exhaust risers or exhaust elbows
will be significantly affected by salt water. These risers
must be inspected annually and replaced as required. It
is not unusual to have to replace these risers every two
or three years on boats used exclusively in salt water.
Indmar Marine Engines
Some half system installations use the one piece alu-
minum Tri-Y or ETX manifolds and do not have separate
risers or riser gaskets. These manifolds have shown to
be extremely resistant to salt water damage and should
provide extended service over the two piece cast iron
systems, but still need to be flushed regularly with fresh
water to maintain their integrity.
Fresh Water Cooling – Full System – Salt Water
Series Engines
Some fresh water cooling systems are referred to as full
systems. A full fresh water system includes the exhaust
manifolds as part of the system that is cooled with anti-
freeze. Most commonly, a block-off plate is installed
between the exhaust manifolds and exhaust risers and
the risers are cooled with raw water.
Because the risers are exposed to salt water they are
subject to corrosion. These risers must be inspected by
your dealer annually and replaced as required. It is not
unusual to have to replace these risers every two years
on boats used exclusively in salt water.
Some Full Fresh Water Cooled engines equipped with
ETX or Tri-Y one piece exhaust manifolds do not have
separate exhaust risers. Full FWC systems utilizing
those manifolds use anti-freeze in the complete mani-
fold/riser assembly and will not have the riser corrosion
issues associated with the two piece manifold/riser
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