Outboard Engine Manifolds, Risers, Elbows & Exhaust Components

Boat Motor Manifolds, Risers, Elbows, and Exhaust Components Resources and Information 

Manifolds, risers, elbows & exhaust components are necessary for performing periodic service and repairs on your outboard engine. PartsVu offers a complete selection of these essential components from top boating product suppliers, including Sierra, Barr Marine, Shields Hose, Trident Hose, Centek, Sea-Dog, and others. Need help servicing your outboard engine? PartsVu also occasionally publishes helpful resources like the following: 

• Outboard Service Schedule
• Outboard Specs & Capacities Chart
• Mercury Outboard Service Schedule
• Mercury Outboard Specs & Capacities Chart
• MerCruiser Inboard Maintenance

Looking for more marine products for your boat and outboard engine? Browse PartsVu’s products and accessories or aftermarket engine parts.

Outboard Engine Manifolds, Risers, Elbows, and Exhaust Components FAQs

What is an outboard engine manifold? 

During combustion, all engines produce fumes. Without anywhere to go, these toxic fumes would build up in your engine, possibly poisoning passengers and contributing to environmental destruction. The marine exhaust manifold collects these fumes and channels them into the exhaust system. From there, the fumes are treated to remove any noxious elements before being expelled through the exhaust pipe.

What do outboard engine manifold risers do? 

In addition to channeling the exhaust fumes out of the combustion chambers, the manifold is largely responsible for cooling the engine. The risers help the manifold achieve this by extending the manifold and connecting it to the exhaust hose. Risers also prevent water from entering the exhaust manifold. 

Sometimes called “elbows,” risers are typically L-shaped with one opening at each end. One end connects to the aft of the outboard engine manifold, while the other end connects to the exhaust hose. To withstand the heat of the exhaust and to assist in cooling the engine, risers feature a two-layered construction. Cooling water passes through the outer layer, forming a water jacket around the inner layer, through which exhaust fumes pass. In turn, the hot exhaust fumes are cooled by the water, so that by the time the fumes reach the exhaust hose, they are cool enough to avoid damaging the hose material. 

How do I take care of my outboard engine manifold risers?

Manifold risers are commonly made from cast iron– a highly durable material that is also prone to corrosion. Corrosion can occur even quicker if you run your outboard engine frequently in salt water. If corrosion is allowed to accumulate for too long, it can compromise the riser’s material, leading to failure and overheating. For this reason, we recommend replacing your risers every four to five years. If the inner layer of the risers becomes corroded, cooling water can penetrate the exhaust system. If the water finds its way into the cylinders, it can result in complete engine failure. An entire outboard engine will cost much more to replace than a couple of risers. To avoid engine failure, keep track of the intervals between manifold replacements and don’t wait too long to replace them. 

How do I know if my riser is leaking? 

If your engine is having trouble starting, it could signify riser leakage. Another common symptom of a leaking riser is white smoke. If the riser is failing, hot exhaust fumes will end up in the exhaust hose. Using an infrared pyrometer, you can check to see if your exhaust hose is too hot, it indicates that riser failures is occuring.

What are the signs of a damaged exhaust manifold? 

While manifolds are designed to withstand high temperatures and harsh marine conditions, damage can still occur from time to time. If you notice any of the following signs, it may be time to replace your outboard engine’s exhaust manifolds. 

• The smell of burning plastic or rubber - If you smell burning rubber or burning plastic when operating your outboard engine, it’s possible that you’re smelling the rubber or plastic coating on your manifold gaskets burning as a result of the manifold overheating. 
• Poor performance - If your engine suddenly starts running slowly or loses power, a loose exhaust manifold could be the culprit. 
• Loud exhaust - If you notice that your exhaust sounds louder than usual, it could be a result of a hole in your manifold. Holes could be caused by corrosion or damage. 

How do I service my 4-stroke outboard engine?

Use an appropriately sized screwdriver assisted by a wrench if necessary to loosen these screws which should be pretty tight. An impact driver and hammer might be needed. If the drain screw has a magnetic tip, inspect the plug after removal to see if heavy deposits exist. Some fine shavings are normal, but chunks or a large quantity of metal is cause for further inspection. Have a drain pan ready, and extra rags handy as gear lube will begin running down the skeg as soon as you remove the upper vent plug. Be sure to collect the used gaskets from both plugs after removal as these are not reusable and should be discarded.

Allow several minutes with the engine tilted all the way down to drain all the old gear oil fully. Like your engine oil, inspect the spent oil for evidence of water intrusion, other contamination, or metal. If you have purchased one of PartsVu’s handy lower unit oil change kits, you will already have new gaskets, oil, and a pump. Screw the pump into the lower drain hole, then connect it to the container of gear oil.

Begin pumping oil into the Mercury lower unit until oil begins to flow from the vent plug at the top. Stop pumping and wait a few minutes for all the air bubbles to work themselves out of the gearcase. After this brief pause, pump a few more times until clean gear oil without bubbles is flowing from the vent plug. With a fresh gasket in place, install and torque the top vent plug. Unscrew your fill hose from the lower drain plug and quickly swap in the lower drain plug with a new gasket — torque to spec.

Before you do get started on any maintenance projects, make sure to get the right parts (even for Mercruiser engines) so you don’t have to stop right in the middle.

What is an outboard leak down test?

An outboard leakdown test is a simple diagnostic checkup for your outboard – and it can even be incorporated into your regular maintenance intervals for peace of mind. 

During the test, you’ll be able to determine if there’s any loss in air pressure around your engine’s internal seals and passages. Even a pinhole leak can drastically alter your outboard’s performance, so performing a leak down test is important to determine whether the piston seals and other components are in good shape. 

Fortunately, a leak down test only requires a few common tools and some basic knowledge about your outboard. Even boaters with minimal experience can diagnose developing issues that affect the overall performance and lifespan of your boat’s engine(s). Best of all, performing this test will save you money and headaches down the road.

A outboard leak down test indicates the condition of each of the engine’s cylinders and the overall condition of the motor. Similar to a compression test, it involves spraying compressed air into each cylinder and using a pressure gauge to measure a percentage of pressure that’s lost after a short period.

Also, part of doing a leakdown test on a motor is to listen for any signs of leakage. By listening closely to each cylinder and the areas around them, you’ll better understand where leaks may be present.

The goal of a pressure test is to confirm whether the motor has any air leaks. The presence or absence of air in engines often leads to leaking of fuel-air mixtures and leakage of fuel during operation. 

Additionally, these leaks may become infiltration points for water and moisture from the aquatic environment, resulting in internal corrosion, sub-optimal performance (i.e., at idle, low RPMs, and high RPMs), and other issues.