Marine Manifolds

Marine manifolds, by the nature of their function, suffer great strain. Hot exhaust gases and cooling waters flow through them. Marine engine manufacturers use a variety of different designs to reduce the damage caused by this corrosive mixture.

Today almost all manifolds are tempered cast iron to resist the damage caused by the expansion and contraction. Some even have proprietary, patented coatings to help them withstand the stress. While metal quality for the original exhaust manifolds differs only slightly, there may be substantial differences in quality among the various aftermarket manufacturers and even within individual aftermarket product lines. That being said, the price of aftermarket manifolds is generally lower.

A marine engine's cooling system has a direct impact on the life of both exhaust and intake manifolds. Marine engines have one of two different cooling systems: fresh-water (closed) cooling or raw-water (open) cooling. Both systems use some form of raw-water pump that pumps water from outside the boat. For example, in a Volvo engine the pump is inside the boat and driven by the engine. However, in a Mercruiser engine the raw-water pump resides in the outdrive.

In a raw-water cooling system the raw-water pump pushes the water into the engine's circulating pump which in turn circulates the water throughout the block and intake manifolds, then out through the exhaust manifolds and risers. While all water will cause rust, salt water is particularly corrosive and this corrosion increases when an engine has long periods of inactivity. Some people make sure that they run fresh water through their engine after they have been in salt water to help reduce corrosion to the manifolds.

In a fresh-water cooling system, the raw-water pump pushes the water through a heat exchanger and then out through the risers (not the manifolds). The engine's circulating pump circulates the anti-freeze/water mixture throughout the engine and the intake and exhaust manifolds and is cooled by, but does not come in contact with, the cool raw water. The heat exchanger is similar to a car radiator, and the raw water cools the circulating anti-freeze instead of air moving though the radiator. This system lengthens the life of manifolds because they do not come in contact with raw water and the anti-freeze mixture contains anti-corrosive chemicals.

Finally, you may be interested to know that you can buy additive products to protect marine manifolds (not to mention marine engines) from the corrosion and decay caused by salt water. Volvo Penta's Neutra-Salt system delays the onset of corrosion. The Neutra-Salt solution mixes with raw water when it enters the engine, and (as its name would suggest) neutralizes the damaging effects of salt in the water. Neutra-Salt systems are easy to set up and maintain, making them an excellent option for boats that operate frequently in salt-water environments. Neutra-Salt, originally designed for boats that with raw-water cooling, is cost-effective enough that many people now use it with freshwater-cooling as well to help protect the risers.

Protecting Marine Manifolds
If you are interested in learning more about how to protect marine manifolds from salt and rust, contact the experts at Marine Parts Express. We carry manifolds, fresh-water cooling systems, and additives like Neutra-Salt. Steps taken to preserve manifolds will save boaters money in the long run and also prevent engine damage caused by cracked or improperly functioning manifolds. For information about marine engine procedures and precautions, contact us at (877) 621-2628 or e-mail us at info@marinepartsexpress.com.