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Old 19-01-2015, 09:13   #16
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Re: How is the water getting into my engine?

One more thing. Japarker11 mentioned a loop in the raw water side. The engine is fresh water cooled (sealed system) so seawater only goes to the heat exchanger and then out through the exhaust. The coolant level on the engine has never dropped so I don't think the water is getting from there. If it was, it would be happening all the time and this has happened twice in ten or eleven years, both last season.

Sorry for being so wordy, kind of thinking while I type.

Grant
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Old 19-01-2015, 10:20   #17
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Re: How is the water getting into my engine?

Grant,

The advise from Japarker11 is worth looking into. In a fresh water cooled engine the raw sea water should go out of the heat exchanger then up to a very high loop (above the heeled waterline) with an anti-siphon break. Then the hose comes back down to the exhaust elbow. It should not go directly from the heat exchanger to the exhaust elbow with a short hose. If there is no siphon break in that path then there is the possibility for sea water to flow continuously even when the engine is off. That could possibly fill the muffler with water then back up into the exhaust manifold and fill a cylinder with water.

At the top of the loop between the heat exchanger and the exhaust elbow there should be a siphon break device. If the siphon break is plugged up with salt or other crud then it won't work and can cause the problem you have.
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Old 19-01-2015, 10:47   #18
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Re: How is the water getting into my engine?

loop vacumm break and flapper valve on the outsdie transo. if the eahaust is big enough we usedto shove a tennis ball through the exhaut on the outt transo when running down wind. we had a string going through it becasue when you froget its there the tennis ball blows out
skin valve on insdie at transo is best but usually a pain to get too every time you want to start the engine
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Old 19-01-2015, 11:01   #19
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Re: How is the water getting into my engine?

Grant, a side note, change your oil. Any time water gets into a cylinder, some will get past the rings into the sump. You dont want salt anywhere near your cam,lifters etc. ________Grant.
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Old 19-01-2015, 12:26   #20
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Re: How is the water getting into my engine?

Do you have an anti-syphon loop on your exhaust hose exiting the stern of your boat? If not, you may be inadvertently siphoning seas down into your engine when you are going downwind with bigger following seas. The exhaust hose must go up high enough up into an antisiphon loop so seawater cannot go up through your exhaust exiting hose.
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Old 19-01-2015, 13:18   #21
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Re: How is the water getting into my engine?

WATER in the ENGINE
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Old 19-01-2015, 13:51   #22
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Re: How is the water getting into my engine?

The exhaust loop is not high enough if under the cockpit sole. Change it to loop in the lazarrette above the exit. (inside the stern of the boat) Then do as noted above regarding a siphon break on the raw water hose prior to the exhaust elbow... although I lean toward the exhaust being the issue.
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Old 19-01-2015, 14:48   #23
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Re: How is the water getting into my engine?

following seas with water splashing in the exhaust while engine off: put a gate valve on the exhaust (be sure its open to start)

vented loop not installed or plugged up so water is siphoning after shutoff. remember it has to vent above the waterline on either tack.

Bad mixing elbow.

bad heat exchanger or cracked head or block. (this will lead antifreeze in if you are fresh water cooled).
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Old 19-01-2015, 15:21   #24
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Re: How is the water getting into my engine?

In heavy weather your exhaust may experience times where the ocean is considerably above the top of your system and the force of the water may be such that it forces it's way into your engine. A common fix is to instal a valve aft of the muffler and below and aft the high point in your exhaust pipe.
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Old 20-01-2015, 12:39   #25
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Re: How is the water getting into my engine?

Quote:
Originally Posted by Grant Gordon View Post
Thanks for all the replies so far. A couple of people have mentioned anti-syphon valves and I am curious. In my original post I mentioned mixing elbow but what I really have attached to the exhaust manifold is a Westerbeke "exhaust elbow riser" (their name, not mine) similar to this:

Westerbeke 37403 Sailboat Supplies, Engine Parts and Boat Parts

Would something like this have a back flow preventer or anti syphon in it by default? If it does and that has failed, it is most likely where my problem is.

Cheers,

Grant
It may accomplish some protection from positive pressure in the raw water feed with the engine off.
I had incorrectly assumed that the vanes in the raw water pump would effectively thwart surge pressure from a swell. This is more correctly addressed by a vented loop which is located upstream of the Johnson pump and opens under positive pressure and closes under the vacuum of the suction of rotating pump.




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Old 20-01-2015, 13:21   #26
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Re: How is the water getting into my engine?

Quote:
This is more correctly addressed by a vented loop which is located upstream of the Johnson pump and opens under positive pressure and closes under the vacuum of the suction of rotating pump.
That is not how a vented loop works. A vented loop is upstream of the pump and closes from the pressure that the raw water pump produces and opens when that pressure drops thereby preventing water from siphoning into the exhaust system.
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Old 20-01-2015, 14:05   #27
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Re: How is the water getting into my engine?

The below discussion is related to engines that are mounted below the water line or can be below the water line when the boat is heeled. Thus many power boats don't have an anti-siphon. But most sail boats do have it or at least they should have it.

I think we might be confusing one another by "upstream" and "downstream". There is no vented loop in the hose that carries sea water between the through hull and the raw water pump. The outlet of the raw water pump generally feeds water through one or more heat exchangers. It might cool the oil of the engine and/or transmission. Then the sea water usually goes to the main engine heat exchanger last. In this entire path from the through hull to the engine heat exchanger there is almost never any vented loop or backflow preventer.

Once the hot sea water leaves the main engine heat exchanger the water hose usually rises up to the highest possible point in the boat. There it will pass through an anti-siphon device. This device will be open if air is present but as soon as water hits it then it closes. Some boats (like mine) don't have a valve but they have a small hose that goes to the hull and lets a little water dribble out. Then from this high point in the system the hose goes down to the exhaust elbow. This anti-siphon must always be above the water line at all angles of heel else the anti-siphon feature will not work. That is why it is always as high as possible above the engine.

As soon as the raw water pump stops running some water will still flow down from the high point into the exhaust manifold. This will create a small vacuum at the high point and air will enter the hose there through the anti-siphon. This air stops any chance of siphoning action. If this high point does not allow air to enter because the anti-siphon device is plugged up with gunk then water can continue to siphon from the ocean into the muffler. Eventually the muffler will fill up and then the siphon will continue to fill whatever cylinders of the engine happen to have their valves open.

Some boats have a high loop in the exhaust hose. This is not what I am talking about in the above discussion. The high loop in the exhaust hose is just there to prevent water from being pushed into the muffler from a following sea. It does not usually have any anti-siphon device. There is too much risk that exhaust gases might leak out into the interior of the vessel.
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Old 20-01-2015, 15:00   #28
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Re: How is the water getting into my engine?

Quote:
Originally Posted by Grant Gordon View Post
Thanks for all the replies so far. A couple of people have mentioned anti-syphon valves and I am curious. In my original post I mentioned mixing elbow but what I really have attached to the exhaust manifold is a Westerbeke "exhaust elbow riser" (their name, not mine) similar to this:

Westerbeke 37403 Sailboat Supplies, Engine Parts and Boat Parts

Would something like this have a back flow preventer or anti syphon in it by default? If it does and that has failed, it is most likely where my problem is.

Cheers,

Grant
An extended riser like this is used when needed (engine located too low relative to the muffler) to create sufficient vertical distance between the exhaust gas discharge and the muffler so that the gas/seawater mixture has ample opportunity to cool before it reaches the muffler. It also provides some additional protection (only several vertical inches) from reverse flow from the exhaust system entering the exhaust manifold and cylinders, but that is not really its purpose.

Since the water entry has apparently occurred only during heavy seas, the two most likely ways in which sea water could enter the engine with the engine off are: 1) following seas could enter the exhaust hose and flow back to the engine if, as you have described, the exhaust hose does not run to a high point between the muffler and the stern that is well above the maximum sea level. Or, 2) a siphon is established in the sea water intake/raw water pump/ heat exchanger/mixing elbow circuit. This can occur if there is no elevated loop with anti-siphon valve installed between the heat exchanger and the mixing elbow, or if there is an anti-siphon valve and it is not working properly (not admitting air in sufficient quantities). Your responses suggest that there is no anti-siphon loop in your set up.

To be confident that water will not enter the engine, you need an elevated loop with a working anti-siphon between the heat exchanger and the mixing elbow and you need to route the exhaust hose between the muffler and the stern up to a high point as close to the rail as possible and the high point should be located as close to the muffler as possible. If this is impractical, valves are an option as discussed in several of the posts, but obviously complicate every day operations.
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Old 20-01-2015, 15:22   #29
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Re: How is the water getting into my engine?

There is on more possibility, if you have a "dripless stern gland" installed.
This unit relies on a positive pressure raw water connection.
In our situation the hapless installation engineer put a loop in the line but did not install a syphon break.
The result was when at anchor in a bay where the boat rocks fore and aft the stern gland created a pump action that eventually back filled and flooded the engine with water.
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Old 28-06-2015, 17:33   #30
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Re: How is the water getting into my engine?

Just to close the loop on this thread, in the end it was the Westerbeke mixing elbow. Corroded and leading at the top where the water enters. Replaced and all is well now.
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