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Old 05-02-2013, 15:35   #31
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Re: Need some help from the diesel gurus

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If the motor is turning over but not firing you'd better shut the raw water intake. If you do not you can fill the cylinders with water and if it fires it will ruin the engine. Bend piston rods, shear crankshaft bolts and more. This is a condition called hydrolock.
Mate..........I don't know how your motor works but in mine the raw water and the cylinders are totally separate. No amount of cranking will fill the cylinders with any water!
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Old 05-02-2013, 15:39   #32
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Re: Need some help from the diesel gurus

Another thought.............

Is there a valve on the exhaust pipe anywhere. Maybe to stop back flooding via the exhaust pipe. It may be closed. Too much back pressure will prevent a diesel from starting, particularly a small one.
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Old 05-02-2013, 15:48   #33
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Re: Need some help from the diesel gurus

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Mate..........I don't know how your motor works but in mine the raw water and the cylinders are totally separate. No amount of cranking will fill the cylinders with any water!
This is a valid concern and is very possible.

Raw cooling water is injected into the elbow fitting at the end of the exhaust manifold. This is to cool the exhaust gases going out hose and to the stern of the boat.

Crank too long and you get a lot of raw water injected into the exhaust pipe but no exhaust gas from the engine to push it down the hose and out of the boat. So more water collects in the exhaust hose, manifold fills up and water comes back into the exhaust valves and into the cylinder.

Unless you have a hot, dry exhaust yours will be set up the same way and raw water can indeed get into your cylinders.
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Old 05-02-2013, 15:52   #34
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Re: Need some help from the diesel gurus

My 6" wet exhaust is all downhill from the mixer. No amount of cranking will fill anything with water!
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Old 05-02-2013, 16:15   #35
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Re: Need some help from the diesel gurus

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This happened to me last year. I had a Volvo MD IIc. Got up at O dark thirty so that we could make a passage in daylight hours. Went to start the engine. Couldn't get it to start. Sounded like the battery was weak. Finally after messing with it for three or four hours I got it to start. I held a board over the air intake covering up most of it. According to Nigel Caulder this get the engine to spin faster. Engine started. Let it run for an hour. Turned the engine off to see if it would start again. It wouldn't. Took it in to a mechanic. He thought the battery was dead. We charged the battery. Wouldn't start. Changed the battery to another that he had. Wouldn't start. Took the starter out and bench tested it. Bearing on the starter was bad so that the case was out of center. Engine would turn fast for 3/4 of a rotation of the starter then slow down. The magnet in the windings would catch on the case of the starter and then the starter would have to break that connection so the starter never got up enough speed. The mechanic changed the bearing and it worked. If it isn't too hard I would have the starter bench tested.

This idea of Charlie's is where I place my bet... Bad starter and now all the connections in the path are compromised due to the high amp load of a bad starter... Get a multimeter with a DC clamp ammeter (cheap @ harbor freight) ...

I have used the restricted airway method MANY times to get a diesel spinning faster... when a crowd is watching, you look like Einstein when she fires...


Good luck!
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Old 05-02-2013, 16:58   #36
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Re: Need some help from the diesel gurus

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Another thought.............

Is there a valve on the exhaust pipe anywhere. Maybe to stop back flooding via the exhaust pipe. It may be closed. Too much back pressure will prevent a diesel from starting, particularly a small one.
+ 1 I had the same problem before with an volvo MD2... It had a drain plug on the exhaust.
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Old 05-02-2013, 17:03   #37
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Re: Need some help from the diesel gurus

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Mate..........I don't know how your motor works but in mine the raw water and the cylinders are totally separate. No amount of cranking will fill the cylinders with any water!

You obviously don't understand hydrolock in diesel powered sailboats.. Do a search and save us explaining. Hydrolock is a very real possibility with the OP's boat.
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Old 05-02-2013, 17:06   #38
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Re: Need some help from the diesel gurus

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My 6" wet exhaust is all downhill from the mixer. No amount of cranking will fill anything with water!
In that case you have probably have no concern with backflow but there is a potential link between the raw water and the cylinders.

However, lots of boats the engine is mounted very low in the boat and it's pretty easy for raw water to backflow into the cylinders.
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Old 05-02-2013, 17:32   #39
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Re: Need some help from the diesel gurus

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You obviously don't understand hydrolock in diesel powered sailboats.. Do a search and save us explaining. Hydrolock is a very real possibility with the OP's boat.
Wrong! I totally understand hydraulic locking of the cylinders! It is just an issue of which fluid and how it gets in!

FYI..... I am a diesel engineer., amongst other things.


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In that case you have probably have no concern with backflow but there is a potential link between the raw water and the cylinders.
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Old 05-02-2013, 17:53   #40
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Re: Need some help from the diesel gurus

Even if the batteries are showing more than 12volts, they still may be part of the problem. Have you load tested them ? Weak batteries also help premature failure in starters.
So if the batteries test out good , all the connections are clean and tight and you still have dimming lights and slow cranking pull the starter and get it looked at and rebuilt if needed. I know less than zero about sail boats but have been a diesel mechanic for almost 30 years. Hope this helped.
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Old 05-02-2013, 18:03   #41
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Re: Need some help from the diesel gurus

40 south, As a diesel engineer you should do some research on diesel installations on SMALL vessels. With engines that are at or below the waterline there is a very real danger of filling your exhaust system to the point of back filling into the cylinders. This is an old and recognized problem in small boats(as opposed to large stationary diesels). It is one of those tidbits of info that isnt always known unless there has been some training in small boat diesels. Even if the exhaust doesnt fill to the point that it flows back into the cylinders, it can cause enough back pressure to make the engine harder to start. It is real! It can, and does happen._____Grant.
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Old 05-02-2013, 18:20   #42
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Re: Need some help from the diesel gurus

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Wrong! I totally understand hydraulic locking of the cylinders! It is just an issue of which fluid and how it gets in!

FYI..... I am a diesel engineer., amongst other things.



This thread is intended to help the OP. We have no concern regarding how your engine works. You may be a diesel engineer but obviously are not aware of hydrolock in sailboats It's a very real possibility and my post was to try and make the OP aware of the problem.

Your reply to my original post in this thread:

"Mate..........I don't know how your motor works but in mine the raw water and the cylinders are totally separate. No amount of cranking will fill the cylinders with any water!"

As said earlier I am not concerned with your motor and your reply seems to indicate that hydrolock cannot occur in the OP's motor. You are clearly wrong. I posted in an effort to help the OP. I don't know what the intent of your post was but it clearly will not help the OP.

Have a nice day. If you have a suggestion for the OP's problem we all would be glad to hear it.
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Old 05-02-2013, 18:27   #43
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Re: Need some help from the diesel gurus

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40 south, As a diesel engineer you should do some research on diesel installations on SMALL vessels. With engines that are at or below the waterline there is a very real danger of filling your exhaust system to the point of back filling into the cylinders. This is an old and recognized problem in small boats(as opposed to large stationary diesels). It is one of those tidbits of info that isnt always known unless there has been some training in small boat diesels. Even if the exhaust doesnt fill to the point that it flows back into the cylinders, it can cause enough back pressure to make the engine harder to start. It is real! It can, and does happen._____Grant.
Accepted, not disputing.
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Old 05-02-2013, 18:28   #44
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Re: Need some help from the diesel gurus

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Mate..........I don't know how your motor works but in mine the raw water and the cylinders are totally separate. No amount of cranking will fill the cylinders with any water!
Each time the motor spins while cranking, the raw water impeller pulls in water and spits it into the exhaust elbow. Most sailboats have the exhaust pipe and water lift muffler below the elbow. Too much cranking without starting and the muffler fills up and starts oozing raw water into the exhaust and cylinders. It's basic boat knowledge and I've seen more than one damaged by it.
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Old 05-02-2013, 18:32   #45
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Re: Need some help from the diesel gurus

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Have a nice day. If you have a suggestion for the OP's problem we all would be glad to hear it.
Read post #32. I am offering suggestions!

Read post #43. End of discussion re hydraulic lockup. Getting off topic. I expect OP gets the idea!
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