|BAD EXHAUT IS THE #1 REASON
for blown engines! Maintain your's
well. (see below)
Boat Exhaust manifolds last forever, don't they? Even if they do fail, it isn't a major problem, right? These are common reactions when
people are asked about their boat's manifold. Unfortunately, exhaust manifolds are important, and ignoring them can potentially lead to
expensive problems, perhaps an engine rebuild. There is an additional hassle-manifolds are normally damaged by corrosion, so they're
not covered by your insurance policy.
All of this makes the outlook seem rather bleak. It's not as bad as it seems, though. All that's needed is a change in attitude. Rather than
seeing it as a "sealed for life" component, view a manifold as a service item to be replaced at regular intervals, and always replace in
pairs. If you do this, major problems can be avoided.
How long will a boat manifold last? Obviously the way you use your boat will be a factor, as will the type of water it's on. Saltwater boats
are going to see a shorter manifold life when compared to their freshwater counterparts. Most experts suggest that a manifold will have
a life expectancy of five to seven years. However, heavy use in saltwater can see this drop to as low as three years, while lightly used
freshwater boats can get up to 20 years out of a manifold. One thing is for certain, the older your manifold gets, the more likely it is to
fail. This is clearly shown in the chart below.
Years in Service = Probability of Failure
3 years = 0.5%
4 years = 25%
5 years = 45% (recommended replacement time)
6 years = 65%
7 years = 85%
8 years = 90%
9+ years =100%
Why So Fragile?
The marine manifold is a complex metal casting, actually a pipe within a pipe. It feeds hot exhaust gases and water to the riser where the
gases and water combine to continue their trip overboard. Without the cooling effect of the water, the hot gas would burn through a
hose or thin wall pipe very quickly. Keeping the water and gases separate in the manifold is critical. If water finds its way into the
gas-only section, it can enter the engine cylinders and wreak havoc with the internal engine parts.
Manifolds and risers live in an incredibly harsh environment. They endure very hot corrosive gases slamming into the manifold at high
velocity. The water jacket portion of a manifold is intermittently exposed to hot saltwater and moist air, the perfect conditions for
corrosion. All the time they're vibrating madly during running time and left idle for long periods, allowing rust to eat away at the metal.
That they last as long as they do is impressive.
Before your manifold fails, you "may" get warning signals. Needless to say, you should take notice immediately. If your engine is difficult
to start, produces white smoke, or runs roughly, water in the cylinders may be the culprit. If you ignore the situation, hydrolock may
occur. This is when sufficient water has leaked into the cylinder that piston compression becomes impossible. Massive, and usually
terminal, damage will result as you try to start the motor.
Inspection is always a good idea, and we recommend that you try to do so at least every two to four years. It may seem a little pointless
since it's impossible to see into all the passages, but you will still get some clues about the extent of any corrosion. Your manifold may
be blocked with the products of corrosion, for example, leading to "hot spots" in the cooling system and low-level overheating. These
won't necessarily show up on your temperature gauge, but can result in a shortened engine life.
If your boat suffers more than average corrosion problems, then it may be more likely to suffer from premature manifold failure. Stray
current corrosion is evidenced by rapid zinc wastage, corroding lower units and corrosion build-up on through-hull fittings. This is
normally the result of poorly installed 12vDC/110ac wiring or faulty 12vDC/110ac equipment. Electrical problems should be corrected as
soon as possible; the damage caused by leaky 12vDC/110ac wiring is potentially far worse than a broken manifold.
Replacing a boat manifold is certainly a job that you can do yourself. It may take longer than you expect, though. Bolts may be rusted in
place and other fittings may be in your way. It can turn out to be a day-long job. If this does not appeal to you, boatyards will tackle the
job for you.
If you decide that your manifolds and risers are nearing the end of their service, and you don't want to interrupt the boating season with
a blown engine, replacements are available here or by calling the Boat store. You will need the make, model and serial number of the
engine, the exhaust pipe diameter, and will need to order the necessary gasket kit, installation kit, and end plates if required.