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post #11 of 15 Old 04-17-2013
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Re: Exhaust Manifold Flooding with Cooling Water

Overwhelming...I don't think so. A marine thermostat is usually set up as a "t" diversion valve, in which case the flow might be a problem. But if it was set up automotive style, slow engine = cold engine = flow shut down, so no flooding problem?

Seems like it would need some attention but the actual engineering of it, whichever way, shouldn't be impassible. Waterlift exhausts can be a mixed blessing, huh?
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post #12 of 15 Old 04-17-2013
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Re: Exhaust Manifold Flooding with Cooling Water

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Originally Posted by hellosailor View Post
Overwhelming...I don't think so. A marine thermostat is usually set up as a "t" diversion valve, in which case the flow might be a problem. But if it was set up automotive style, slow engine = cold engine = flow shut down, so no flooding problem?

Seems like it would need some attention but the actual engineering of it, whichever way, shouldn't be impassible. Waterlift exhausts can be a mixed blessing, huh?
I do not follow.

With most diesels, all the water that gets pumped by the raw water pump exists through the exhaust mixing pipe. So say you want to use an electric raw water pump. The pump needs to be sized to pump at a flow rate your mechanical pump would pump with engine at WOT. Now say your engine is at idle and your electric pump is pumping at the WOT rate. I would think you could risk back flowing into the exhaust manifold and engine cylinder.

Now say you want to shut the engine down. You would need to stop the electric raw water pump at the exact time (or maybe slightly before) the engine stopped or otherwise the cylinder would be flooded with water.

There is no practical way an electric water pump could work on a raw water cooled engine. The mechanical water pump running off the engine however self regulates in a beautiful manner. We are lucky for that.
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post #13 of 15 Old 04-18-2013 Thread Starter
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Re: Exhaust Manifold Flooding with Cooling Water

I did some reading about electric raw water pumps. The most practical setup I found was one in which the pump was controlled by an oil pressure actuator -- oil pressure comes up, pump goes on, oil pressure drops, pump goes off.

But I've pretty much abandoned the idea, at least as a way to reduce the likelihood of exhaust flooding. For one thing, it introduces lots of extra complexity (which is inversely proportional to reliability). For another, as has been recently pointed out in this thread, a mechanical pump is somewhat self-regulated -- at cranking speeds, it doesn't pump very much, and by the time it's running at normal pumping speed, the exhaust gases are clearing the exhaust. And lastly, a good pump is quite a bit more expensive than I had anticipated (not to mention the cost of controls, wiring, hoses, etc.).

At this point, my plan is to install the Speedseal Life (assuming it's made for my engine), which will allow the pump to better tolerate a few seconds with shutoff suction (so I can open the seacock after the engine starts, rather than before).
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post #14 of 15 Old 04-19-2013
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Re: Exhaust Manifold Flooding with Cooling Water

I saw a mechanic quoted on another site as saying f everyone went dry exhaust and keel cooling , us mechanics would all be out of work`. Wet exhuasts are a major source of engine problems.`
Several friends, with water in the engine problems, went dry exhuast, and eliminated all such problems. I would never consider having a wet exhuast.

Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"
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post #15 of 15 Old 04-19-2013
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Re: Exhaust Manifold Flooding with Cooling Water

"I would never consider having a wet exhuast. "
So just what would you fit on a conventional sailboat with an auxiliary engine? Or wouldn't you have one at all?
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