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Old 05-06-2011, 05:56   #1
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Water in muffler question?

This may be a stupid question, but I'm trying to understand how much water is normally retained inside a wet exhaust muffler once the engine is shut down. It makes sense to me that it should be pretty full of water, but I don't know. I ask because I hear sloshing on one side of the boat and not the other (twin engines, hence twin mufflers), and because I have about a 1" list to the side where I hear the water and I can't otherwise figure out where the imbalance is coming from.

Here are some specifics. The mufflers are horizontal Centeks, but they are custom to this boat and glassed into place. They have an oval cross section with the oval standing vertically. Exhaust enters one end in the upper portion of the oval, and exits the other end from the same upper portion.

I don't know what the internal construction looks like, but my presumption given the oval shape and exhaust entering and exiting the upper half, is that the lower half of the muffler fills with water and remains filled. When the engine is running, new water flushes through. There also is what appears to be a drain plug on the end of the muffler which further supports the notion of a water pool.

Is this right? Or is water NOT supposed to accumulate in the lower part of the muffler?
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Old 05-06-2011, 06:06   #2
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Re: Water in muffler question?

Water does sit in the muffler, not sure how much but whatever is full while running These things usually have a drain plug in the bottom if you care to drain then and see
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Old 05-06-2011, 06:44   #3
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Re: Water in muffler question?

I cannot imagine enough water in any muffler to account for a noticeable list.

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Old 05-06-2011, 07:39   #4
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Re: Water in muffler question?

If these are waterlift mufflers, then the answer is "not much water" when compared to the entire volume of the device.

The "output" tubes are dip tubes and extend inside to the bottom of the muffler. Usually, the inside end of the tube is sliced such that it is parallel to the bottom of the tank and sits about an inch (? +/-) above the bottom. This gap dictates the amount of water is "stored" in the muffler. As water is dumped into the muffler, rising above the dip tube, exhaust pressure builds up and forces the water down, up and out of the dip tube.
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Old 05-06-2011, 07:54   #5
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Re: Water in muffler question?

Here is a good image of the workings of a waterlift exhaust. These are not actually classified as a muffler. They are two different things. Chuck
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Old 05-06-2011, 08:28   #6
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Re: Water in muffler question?

Actually, I think that the amount of standing water while the engine is not running is related to the length and diameter of the hose run to the high point in the exhaust system. When the engine shuts down, all the water in this section of the hose drains back into the water lift and is added to the pool in the bottom.

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Old 05-06-2011, 08:49   #7
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Re: Water in muffler question?

The height is related to the height of the discharge tube and the resistance in your exhaust system downstream of the muffler.
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Old 05-06-2011, 09:14   #8
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Re: Water in muffler question?

The level of water static in the muffler, as mentioned above, is a function of the OUTLET level. The thing to remember about these, if mounted below exhaust thru-hull level (normal for a sailboat) is that they will become FILLED with water to the INLET level if the engine is not running and then backup into the engine, creating a "waterlocked" engine and possibility of bending rods if cranked over. This is a little aside from the original question but lots of folks seem to be not aware of the nasty things that happen from cranking a sailboat diesel too much without temporarily disconnecting the raw water.
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Old 05-06-2011, 09:57   #9
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Re: Water in muffler question?

Quote:
Originally Posted by smurphny View Post
The level of water static in the muffler, as mentioned above, is a function of the OUTLET level. The thing to remember about these, if mounted below exhaust thru-hull level (normal for a sailboat) is that they will become FILLED with water to the INLET level if the engine is not running and then backup into the engine, creating a "waterlocked" engine and possibility of bending rods if cranked over. This is a little aside from the original question but lots of folks seem to be not aware of the nasty things that happen from cranking a sailboat diesel too much without temporarily disconnecting the raw water.
A good point, yes. Although, having recently done maintenance on my Yanmar, the "crank over exhaust" (when engaging the starter for a long time) is enough to push out the raw water from the muffler. This may not be a case for an engine with poor compression.

Also, this is a good reason for large volume mufflers. It takes longer to fill them up reducing chance of backup into the engine. I always recommend a custom waterlift muffler sized to the installation space to maximize volume.
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Old 05-06-2011, 10:15   #10
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Re: Water in muffler question?

A little off topic, but still related to water lift mufflers:

A friend of mine with an old gas V8 powerboat found that by wrapping his water lift muffler with lead sound deadener, he quieted his engine by an amazing amount.
It turns out that most of the engine compartment noise had been coming from the muffler housing!
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