Salt water in the diesel engine

Engines, Drive trains, Propellers, Steering, Ground Tackle and other mechanical system
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rds
Posts: 50
Joined: Mon Jul 06, 2009 9:32 pm

Salt water in the diesel engine

Post by rds »

I had weekend full of adrenaline, more that I wanted. Went sailing Saturday morning, motored out of my mooring field as usual, turned off the engine as I normally do, set sails. 15-18 of fresh wind ,excellent weather… Time to go home , coming back to entrance to the waterway discovered that engine did not start. Went down to check and found out that engine did not turn at all…. Managed to get back to my mooring under the sails alone and once tethered to the ball went to engine room. Long story short removed injectors and discovered that engine water logged with sea water! I own this boat for 3 years now never had anything like that before … not even a smallest hint. When I turn the engine off I normally leave raw water seacock opened and if max-prop is spinning I reverse gearbox.. It was fresh breeze so I happily sailed between 7 and 8 knts. all day before coming back . On different tacks: downwind, broad reach , upwind, boat heeled and rolled , not excessively… nothing extra ordinary. As I recall now the last leg home was close reach and probably exhaust was intermittently submerged.
I was changing the oil all Sunday and by the forth change the oil got changed from the brown milky substance to clean, normal oil color. Engine start easily runs the same as before, holds pressure , not overheating, spits water out of exhaust. I ran the engine for a couple of hours to check if everything is normal.. but
It came at me as a complete unpleasant surprise …. I checked raw water cooling system. It seems that everything is originally installed by the factory , no alterations… checked the siphon breaking valve , it functions as it is supposed to. This might happened again… and how to prevent it from happening. Has anyone had the same situation before ? what is the remedy ? is factory installed raw water system has been originally installed incorrectly ?
My raw water system has 2 loops: one is small , about 10-12 inches between heat exchanger and mixing elbow and it has valve on top. The other one is in exhaust, this loop if very big probably 5 feet in total , goes all the way to under the mizzen traveler and thru hull near waterline…
Which way siphon works ?
1) From water intake , raw water pump( bad impeller, worn out pump housing ??), small loop , mixing elbow and into the engine ? or
2) could be from exhaust loop side, floods muffler , mixing elbow , into the engine ?
3) or both ways ?
Any advice is greatly appreciated.

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Rick Simonds
Posts: 144
Joined: Fri Dec 05, 2008 8:49 pm
Location: Tallahassee, FL

Re: Salt water in the diesel engine

Post by Rick Simonds »

I had this happen. I didn't find mine until it messed up the valves. It's good you found it right away and did the oil changes. I doubt you've done any meaningful harm to the engine at all.

It's way more difficult (but not completely impossible) for the water to siphon in from the big exhaust side of the mixing elbow, it almost has to be coming in from from the seawater intake side.

In your system, where is the siphon breaking valve that you mentioned? Also, for the water to get into the combustion part of your engine it would seem like your exhaust manifold must in your seawater cooling system somewhere, too. I really don't remember the exact plumbing for my raw water side step by step (Yanmar 3GMD), but, from memory, my exhaust manifold was originally in the system just before the mixing elbow. To prevent a repeat of my problem, my siphon breaker (which I installed, it did not come from Freedom) is the now in that section. it is the last thing the cooling water goes through just before it dumps into the mixing elbow (From memory: Seawater pump -> Heat exchanger - > Exhaust manifold -> New siphon breaker -> mixing elbow). It is up as high as I could make it. You say you have a "valve" there. Is this an actual valve (like an on/off kind of thing) or is it a "U"-shaped siphon breaker? Either way, I think that device is the key. If it is an on/off valve, I guess you're supposed to shut it off in anything but mild conditions. With it off, no matter what, a siphon can't begin. If it's a siphon breaker the big part of the exhaust system couldn't start a siphon, it could only suck air from the intake side, not water. Same if the big exhaust system after the elbow somehow got pretty full of water: it may suck a little water in but after a while the siphon would break and the engine could only suck air into itself.

A slow day at work today, so my guess from afar, with not much to go on: It's coming in from the intake side, the loop just before the mixing elbow is what to focus on, that's where to break the siphon, and I'm going to make a total WAG that "valve" just before the mixing elbow is actually a siphon breaker and the little air valve screwed into the top of it is stuck closed with sea salt and exhaust crud.
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Rick
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rds
Posts: 50
Joined: Mon Jul 06, 2009 9:32 pm

Re: Salt water in the diesel engine

Post by rds »

Rick, thanks for the input. Here is the diagram of my engine’s installation. I got fresh water cooling system. Sea water cools inner fresh water via heat exchanger. As you can see on the picture the raw water part with two loops :
The first loop with siphon breaker valve (My valve is just a small plastick cylinder at the top of "U", it passes the air in one direction and closes in opposite automatically ). First loop connects heat exchanger with mixing elbow on the exhaust. I also got the second loop in the exhaust itself( gooseneck on the picture). It does not have any valves on top. red lines depict raw water flow: raw water intake scoop -> sea cock -> strainer -> raw water pump -> goes into heat exchanger -> first vented loop -> mixing elbow in the exhaust.
I found a good article explaining faults of wet exhaust systems.
http://www.goodoldboat.com/reader_servi ... xhaust.php
Reading this and some other sources I am now inclined to think that all wet exhaust systems are inherently dangerous and can easily flood engine either via raw water intake( in my case regardless of existing working anti-siphon valve ) or via exhaust (in the article).
Probably that is what happened in my case was that sea water flooded the engine via first vented loop, in my boat this loop rises about 12-15 inches above the water line ( 300 mm on the picture) . I read in the article:
“The water enters by a through-hull and seacock and flows through a raw-water filter. The through-hull may include a scoop. If there is a scoop, it will develop some velocity pressure when the boat is moving. (Six knots produces about 19 inches of water column pressure.). An allowance may be needed when considering other aspects of the system design if there is a scoop facing forward.”
I’ve checked my GPS track and found that my boat hit about 9 kts speed several times on that day. The only thing that stops raw water h beween the non running engine and water intake is the raw water pump while seacock is opened and boat in motion. Ideally the pump is new and impeller seals this path completely , mine is not ... probably the velocity pressure built in the intake path could overcome the head of the first loop and flood the engine combining with the fact that transom sags at the speed and that rise become even smaller ... if someone has similar engine installation what is the height of that loop above waterline in your boat ?As far as I know almost everyone keeps seacock opened while sailing ... I feel that I have to change that habit of mine.
Also does anyone has some flapper valve or some sort of check valve at the exhaust ?
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rds
Posts: 50
Joined: Mon Jul 06, 2009 9:32 pm

Re: Salt water in the diesel engine

Post by rds »

I had my diesel flooded with salt water this summer, the issue described in my previous post. Now with my boat on the hard I want to come up with some sort of rectification . I checked again all the raw water loop and did not find any obvious flaws. Probably I have to replace the impeller and the worn cheek plate on the raw water pump.
One thing I noticed that the raw water intake scoop (see the picture ) facing forward creating some positive dynamic pressure in the intake line while the boat is underway. It looks like the scoop has been originally installed this way by the factory. One possibility is to turn it 180 degree backward, to face stern.
I wonder if it might have some undesirable effect, for instance creating of some negative pressure and therefore leading to less water coming in and possible engine overheating. (I got 4 cyl. 55 hp diesel)
It would be interesting to know if anyone else has the same type of raw water intake and what is its orientation relative to the hull ?
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bad
Posts: 184
Joined: Sat Jul 09, 2011 11:14 am

Re: Salt water in the diesel engine

Post by bad »

We have a huge gate valve at the thru hull for the exhaust. It can be manually shut if there is a large following sea and there is concern about flooding of the exhaust. Our raw water anti-siphon loop is about 2 ft above the water line, and on center line. The thru hull for it is flush mounted and we have an internal Graco strainer.

I don't think you create any problem by flipping the intake screen on your thru hull. I'd make sure the antisiphon valve works and I would try and get the loop as high as possible. Not sure I would close the valve though, unless it is easy to get to and you can open it up quickly if you need your engine. Impeller pumps don't like to run dry. We have a diaphragm pump, which cares less.

Erik

daletournier
Posts: 181
Joined: Wed Aug 18, 2010 6:25 pm

Re: Salt water in the diesel engine

Post by daletournier »

Hi , do you have a water fed dripless seal?
Cheers Dale
Freeform.

rds
Posts: 50
Joined: Mon Jul 06, 2009 9:32 pm

Re: Salt water in the diesel engine

Post by rds »

No, just an original stuffing box with the standard flax packing and it is not connected to raw water loop in any way

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