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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel > Exhaust Manifold Flooding with Cooling Water
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Topic Review (Newest First)
04-19-2013 09:07 PM
hellosailor
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?
04-19-2013 08:59 PM
Brent Swain
Re: Exhaust Manifold Flooding with Cooling Water

I saw a mechanic quoted on another site as saying Őf 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.
04-18-2013 04:43 PM
Rusty123
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).
04-17-2013 09:31 PM
casey1999
Re: Exhaust Manifold Flooding with Cooling Water

Quote:
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.
04-17-2013 09:22 PM
hellosailor
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?
04-17-2013 07:35 PM
casey1999
Re: Exhaust Manifold Flooding with Cooling Water

Quote:
Originally Posted by hellosailor View Post
" In would be imposible for an electric pump to do this "
You are forgetting, there is no need for the electrical pump to mimic a WEAKNESS of the mechanical pump. Regardless of the pump type there should be a thermostat, which is restricting the flow according to thermal needs.

So it doesn't matter how the flow rate from the pump varies, the thermostat has the only opinion that matters there.
Cooling the engine is not a problem, you are right, the thermostat will take care of that.

What I was addressing is overwelming the mixing pipe and flooding the exhaust manifold because the cylinders are not moving fast enough to expel the water injected by the electric cooling pump.
04-17-2013 07:28 PM
hellosailor
Re: Exhaust Manifold Flooding with Cooling Water

" In would be imposible for an electric pump to do this "
You are forgetting, there is no need for the electrical pump to mimic a WEAKNESS of the mechanical pump. Regardless of the pump type there should be a thermostat, which is restricting the flow according to thermal needs.

So it doesn't matter how the flow rate from the pump varies, the thermostat has the only opinion that matters there.
04-17-2013 07:13 PM
casey1999
Re: Exhaust Manifold Flooding with Cooling Water

I thought about the same thing. Have an electric pump as a back-up to the engines mechanical pump. Even thought about using a cheap bilge pump to pump the sea water through the engine. But then I thought about this: The engines mechanical pump flow rate is proportional to its speed. The faster the engine goes (rpm) the higher the mechanical pumps flow rate, and the more cooling water the engine needs (to disipate the higher heat at higher hp output). In would be imposible for an electric pump to do this (unless you want to install a Variable Speed Drive on it). With an electric pump you could flood the cylinders at low or no RPM.

So now I carry a new spare mechanical water pump- should take no more than 30 minutes to change out (and probably more like 15).
04-12-2013 04:18 PM
hellosailor
Re: Exhaust Manifold Flooding with Cooling Water

Rusty, the pro and con of electric-vs-mechanical pumps is an old story. Fuel pumps, oiul pumps, water pumps, air pumps, power steering mechanisms...

If you lose electricity for any reason, you lose the pump. So a direct mechanical pump is usually considered more reliable and cheaper. If you've got faith in your electricity, by all means, you can go electric. Just remember that if you lose electricity for any reason, you'll also have to shut down the engine or burn it out. And if the electric pump has a loose wire or blows a fuse...you have no warning and again, the engine is in danger.
04-12-2013 04:06 PM
Rusty123
Re: Exhaust Manifold Flooding with Cooling Water

So I called to order the SpeedSeal (the US number still connects you to the UK). Turns out that my 2QM15 had two different pumps over the years, one of which they sell a plate for, and the other they do not. So I've got to do some measuring.

But that made me remember a discussion I had with Sen-Dure (previous makers of a fresh water conversion kit for this engine -- see separate thread for details), in which it was recommended that a fresh water pump (if added) be electrical, and mounted to the bulkhead.

I don't think I'll be making the fresh water conversion, but I got to wondering -- why not convert my raw water pump to electrical? Along with making the impeller much more accessible, it would also give me the ability to turn the pump on and off from the engine panel. That way, the cranking/flooding issue is eliminated, because I wouldn't turn the pump on until after the engine starts. Might offer other advantages for engine flushing, etc.

Downside would be lower system reliability, since engine functionality would depend on battery or alternator.

Anyone ever heard of doing this? Any downsides I'm missing?
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