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2004 Mercruiser 3.0L Exhaust Riser corrosion

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pbhughes

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Hi all, looking for some wisdom and advice. Had my 2004 Bayliner on the IC last weekend, and after bringing it home and flushing the engine, noticed several significant sized pieces of rusted metal flushed out of the water side of the exhaust. The largest about 3/4" square and 1/4" thick. The motor is 21 years old and the riser has never been changed, so I imagine, based on the rust, it needs to be. My question is, should I also change the exhaust manifold at the same time? Motor is still running right at 175F as it has always done during normal operations. Starts and runs with no problems, and I don't see reduced flow from the water side of the exhaust.
 
The manifolds usually last much longer...I would say just change the elbow as long as the mating surface of the manifold is still intact...
 
pbhughes said:
Hi all, looking for some wisdom and advice. Had my 2004 Bayliner on the IC last weekend, and after bringing it home and flushing the engine, noticed several significant sized pieces of rusted metal flushed out of the water side of the exhaust. The largest about 3/4" square and 1/4" thick. The motor is 21 years old and the riser has never been changed, so I imagine, based on the rust, it needs to be. My question is, should I also change the exhaust manifold at the same time? Motor is still running right at 175F as it has always done during normal operations. Starts and runs with no problems, and I don't see reduced flow from the water side of the exhaust.
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you are running a 21 yr old exhaust manifold and riser in brackish or salt water? Normal rule of thumb in salt is 5-7 years. I would take it apart and look inside the manifold and riser but safe bet is to replace them vs have water leak back into the engine. You also can acetone test the manifold to see if it is leaking water into the exhaust.
 
If you're in salt water for sure the elbow should be replaced if you see any leaking at the outside of the joint, or every 5-7 years. The manifolds can last longer but at 21 years old, I'd change both, or else risk ruining the engine. I have usually changed both by 7 seasons in salt water. You can test the manifold with acetone but there's no guarantee it won't start leaking halfway through the next season. Why risk an engine to save a few hundred bucks if you're doing the elbow anyway. Do both!
 
OK Acetone has less surface tension than water so if you fill an exhaust manifold with acetone (careful, it is very flammable) it will find leaks that might not show if you fill with water. Prop up manifold level securely and carefully fill with acetone, watch the level of it in the ports for the sealing surface of the manifold. After doing this I recycle the acetone and use it to clean paint brushes lol.
 
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