This is crazy. My exhaust is filling with water and it's flooding the engine

Feb 10, 2004
3,917
Hunter 40.5 Warwick, RI
I had an A4 in my previous boat. The exhaust manifold was connected to a high loop and the water from the HX was injected well below the top of that loop. I never had a siphon break and never had any flooding issues. But the water flow issues are dependent upon the level of the engine relative to the waterline. But a high exhaust loop (mine was insulated) should stop any water from entering the engine EXCEPT if you are cranking and it doesn't start.
 
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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
These sudden symptoms do not suggest a siphon issue. Otherwise the motor would have always had this problem. You say there is a "heat exchanger." Does this motor use antifreeze?

Either way pretty sure what you call a heat exchanger is actually a seawater cooled exhaust manifold. These are cast such that there are two internal passages - one for seawater and a separate one for exhaust gases. Seawater runs through its own passages and around the exhaust passages and so cools things off.

The problem is that the section in the casting which keeps the seawater separate from the exhaust passages has rusted away so that now seawater will go from the pump right into the exhaust passages and so also right into your motor via the exhaust valves.

Charles
 
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Feb 6, 2019
72
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This is a completely new installation. The original A4 had to be replaced. The old engine was raw water cooled. The new install is FWC.

I'll try the vented loop first. I know that's a crucial component and it's currently missing.
 
Feb 6, 2019
72
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Does this motor use antifreeze?
Yes.

Either way pretty sure what you call a heat exchanger is actually a seawater cooled exhaust manifold.
No, they're completely different. Antifreeze flows through the exhaust manifold.

The heat exchanger cools antifreeze with raw water and passes antifreeze back to the antifreeze pump, engine block, and exhaust manifold... then circulated back in to the heat exchanger. In a FWC system raw water never enters the engine.

Heat exchanger photo is attached.
 

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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Understood. Your #4 above was not clear. By the way the anti siphon goes in the hose section - heat exchanger outlet to mixing elbow - and that hose section needs to rise as high as possible as Kloudie said. The mixing elbow should be shaped so as to come off the exhaust manifold, rise and loop (180 degrees) also as high as possible then descend toward the waterlock. Seawater to elbow discharge fitting goes on the downhill (ie waterlock side) of the 180 loop. Make the pipe rise riser loop as high as possible because when that loop is above the waterline a siphon is not possible.

Charles
 
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Oct 2, 2008
3,807
Pearson/ 530 Strafford, NH
At the top of this page there’s a tab with boater info, click there then pick Catalina. There’s a lot of information there for all boats.
 
Feb 6, 2019
72
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I think that was it. I started it up, got it to temp, shut it off and looked for signs of water intrusion.

Did that 3 times. No sign of water in the manifold, by the flange, or in cylinders.

I hope I'm not celebrating too early... but it's looking promising!
 
Feb 14, 2014
7,399
Hunter 430 Waveland, MS
My last point about a high point siphon "breaker".
That breaker must be maintained functional.

But zero flow stops a siphon too.
_____
Boy what a stupid comment by me. Right?

Well...
My sea water pump is a "flex vane positive displacement" type pump.
If that pump vane is new, I get ZERO flow when the engine stops.

Good flex vane impeller = Zero flow = no siphon.;)
____
Moral to the story...
1) Keep your exhaust system clean.
2) Maintain your water pump impeller.
3) Add a High point siphon breaker, as back up.

Jim...
 

Ward H

.
Nov 7, 2011
3,645
Catalina 30 Mk II Barnegat, NJ
Still new to diesels but I thought I read that as an engine cools down after running, the air in the cylinders and exhaust system cools down and contracts. That creates the vacuum that can pull water into the engine.
 
Feb 14, 2014
7,399
Hunter 430 Waveland, MS
That creates the vacuum
Never a vacuum.
I would suspect not very much low pressure either.
If you have a 20 cubic inch piston displacement engine and say 4 cylinders, your actual empty volume on as stopped engine is about half of 20.
Cooling is very slow so not much chance to suck up water by lower pressure.
Also remember at least 2 of those cylinders are partially open to intake air.
Jim...