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A FEW TIPS ABOUT MANIFOLDS AND ELBOWS

Signs of impending failure will be a gradual rise in operating temperature under a heavy load, or difficult starting and rough running when restarting shortly after a shutdown.
Manifolds and risers (elbows) give some warnings before they cause a serious failure. And they usually fail in one of three ways.

  • The most common is that the manifold, or elbow, will rust and flake until the water passages become clogged. This is a gradual occurrence and can be recognized by an above-normal rise in engine temperature when running under a heavy load. The port elbow is usually the first to fail, as this is the hottest spot in the engine. Some mechanics will “tank” the components at a radiator shop to remove the rust and scale. I generally don’t recommend this procedure, as the rust comes from inside cooling passages and it is difficult to tell just how much material is left.

  • In the second type of failure, an inside cooling water passage will break through to the exhaust side. Depending on the extent of the leak, water can enter the combustion chamber and ultimately the crankcase when the engine is shut down. If the engine is running, exhaust backpressure can force water out of the cooling system and again, overheating will result.

  • Finally, a leak can occur in the elbow. This may or may not cause an overheating problem but it will allow water to drain back into the combustion chamber when the engine is shut down. Because of the angle of the boat, it is often the rear cylinder on either side that is affected. A small leak will result in hard starting and rough running until the cylinders clear out and begin to fire. A large leak can cause a hydraulic lock that can bend rods and do other serious damage.


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