How to maintain an exhaust system

The exhaust system on your typical marinised or purpose-built petrol inboard engine consists of manifolds, risers, exhaust flappers and bellows all exiting the vessel on or under the waterline.

The manifold has two sections: the inner allowing the hot exhaust gases to escape the engine as in your typical motor vehicle; and an outer jacket allowing raw seawater to cool the area.

The riser is often bolted to the end of the manifold and allows the gases and water to mix. This is often known as an elbow and, in this configuration, should always have the water flowing down and away from the engine block.

The exhaust flappers are basically a one-way valve that come into play, especially when you are reversing or even when the vessel is on the mooring, to stop any water flowing back to the motor.

All of these parts are subject to highly corrosive gases and high water movement, making them high on the list of parts that will deteriorate rapidly.

Once again our good friends running in fresh water systems may get a longer life than the salty sea dogs.

I would say 99 per cent will respond with: "Why is this so important?"

It’s simple...

These parts are essential to the well-being of the motor. They are serviceable, and replaceable, and are often the cause of total mechanical failure or hydraulic lock to pistons from water entering the block from failure.

More often than not the boat owner will ignore the advice given to him by his mechanic because they look good to the eye.

So what do I do to maintain my manifolds?

MAINTAINING MANIFOLDS
- Manifolds are serviceable. But they are replaced and are not a "repairable."
For servicing your exhaust system, follow the simple steps I have outlined below.

I get exhausted (I see what you did there Gav: Ed) telling boat owners and potential boat owners that manifolds are a must-replace item and need to be factored into your budgets.

There are testing methods available to determine if the manifolds are on their way out. I prefer to use thermography and the use of a thermal camera allows for very accurate testing showing hot spots with high temperature variances.

But for most boat owners, stick to the following basic rules and timelines and you will be keeping your engine running and avoiding a major rebuild.

If you are buying a boat and no records can be shown to give you a reference point, I always recommend the manifolds are replaced at the time of purchase.

FIVE EXHAUST SERVICING TIPS
>> Have your mechanic inspect your exhaust system at each service
>> Remove your manifolds, risers and exhaust flappers every two to three years for inspection
>> Replace your risers, manifolds and exhaust flappers every five years
>> Maintain your water pump and impeller and always have good water flow from the raw water inlet

Following this program will allow for longevity of items like bellows and any hoses and clamps in the system.

It's quite simple and routine, but it still amazes me the number of owners that won’t listen to their mechanic’s advice. He is not into job creation, he is saving you money in the long run.

*Gavin Clark is a contributor at boatsales.com.au and BoatPoint.com.au who writes under the pseudonym 'The Surveyor'. He is a shipwright and marine surveyor with a business called Slipstream Marine based in Sydney. Gavin has 28 years experience in the boating industry, is an avid boater and owner of a 33ft Sharpie (trawler). Gavin can be contacted at boatsurveying.com.au.