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- 2.
How do I go about replacing my exhaust system?
The piping between
the back of the manifold and the inlet to the water-lift muffler
is normally called the "hot section", or "dry section", due to the
fact that this section of the exhaust system is not cooled by engine
cooling water. The only engine part of this system is the flange
which bolts to the back of the manifold. The center of this flange
is threaded to accommodate inch and a quarter pipe threads.
The most common approach is to construct the hot section of the
exhaust out of regular inch and a quarter pipe (black iron, stainless,
brass, etc.). This pipe is available at most local plumbing supply
shops. The hot section should basically extend as high as possible
(no doubt the reason that it is sometimes called a "riser", and
then down to the inlet of the water-lift muffler which should be
mounted as low as possible. This vertical dimension affords protection
against water backing up into the exhaust manifold.
If you're replacing an existing system, it is very convenient to
take the entire hot section to the local plumbing shop and simply
have them match up the same nipples and elbows that were used in
the original system.
Engine cooling water should be introduced just before the water-lift
muffler. You can drill and tap a 1/4" pipe-threaded hole directly
into the piping of the hot section, or install a "T" fitting, with
the stem of the "T" bushed down to receive a 1/4'' male pipe thread
x 1/2" brass hose barb.
NOTE: We now list two different types of water entry fittings to
facilitate the introduction of cooling water into the hot section
(product numbers CSOT_01.1_324 and CSOT_01.2_334). Search on "324"
and "334" (without the quotes) to find them.
Manufacturers of water-lift mufflers like to see 8 inches (or so)
between the water entry point and the muffler, but many boats do
not have the luxury of that kind of vertical space. The Catalina
30 fleet, for example, has barely a foot to work with, due to their
center cabin-mounted engines.
West Marine stocks 4 or 5 different brands of plastic or fiberglass
water-lift mufflers. I'm sure any of these units will work fine.
In case you might want a recommendation, we believe we hear a slight
consensus from among our customers that the Vetus brand may have
an edge in terms of reliability.
In operation, while the engine is at idle, it's common for cooling
water to "batch" out from the back of the boat, as water in the
water-lift muffler sequentially builds up a bit of head while the
exhaust builds up enough pressure to blow it out through the exhaust.
At RPM above idle, there is enough exhaust pressure and volume to
keep the water moving through the system, so no head of solid water
ever builds up.
If you have a copy of our service and overhaul manual, you will
find more details of exhaust system replacement in Chapter 7. -
Updated: March 24, 2004
