8.1s Water Ingestion?

B

btyman11

Member
Mar 23, 2014
94
Long Island,NY
Boat Info
340 Sundancer 2002
Engines
Twin Mercruiser 8.1S Horizon
Hello everyone. Just purchased on 2002 Sea Ray 340 with twin 8.1s inboards with 550 hours. Boat mechanically surveyed well. All compression good on all cylinders. Only issue was slight "residue" on sparkplug #5. I pulled the elbow off on that side and found some very slight rust in the mnaifold as some water was definitely coming back. The elbow looked fine with no corrosion. The exhaust is the "octopus" style and I know at some point on some models there were plastic resonators put into the exhaust tubes and held with clamps about 13-16" from the elbow. The problem on my setup is I dont have 13" to work with. Probably about 9". Dont know what the fix would be here. Does anybody have any feedback or advice
 
Do you have a dry joint elbow "riser" or the standard water jacket "riser"?
 
8.1s are dry joint.

Any idea how old the manifolds are? Possibly a perforation? Did you find a turbulator when you took off the elbow? That is supposed to catch condensate so it doesn't drip back into the exhaust passages of the manifold.

By octopus I guess you mean water lift muffler. That should protect you from ingestion via the under-water exhausts. That was a big problem in earlier 340s with Gen VI 7.4s.

TURBULATOR #19 here...
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My setup is the exactly like the diagram above minus the water rail and spacer. Manifolds were done in 2011. Yes there is a turbulator plate and it's the water lift mufflers.
 
The rail was the old aluminum manifolds. Sorry. Should have not used that pic.
 
The very slight corrosion/rust is definitely from water coming back into manifold as it right near the top of where #5 would be.
 
Not sure what could cause that. Hopefully someone smarter than me will chime in. Short of that I guess I'd monitor it carefully. 2011 manifolds aren't old enough to get corroded, even in Long Island.
 
Yeah I kind of figured the manifolds are good. That piece in the diagram (#32) would be a fix but unfortunately I dont have enough length in the exhaust tube. By putting it too close might change the back pressure I would think.
 
Could it be that during winter lay-up, moist air blows into the exhaust and causes that bit of rust? I've always stuffed rags in all exhausts to minimize this. Some people take the exhaust hoses off completely.
 
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