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Old 04-23-2011
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Diesel Engine damage

HI,

I am a new boat owner and new here on the forum and I have generated an interesting concern right out of the box.

I tried and succeeded starting up my 1983 35 HP Universal Atomic Diesel Engine, with the engine exhaust thru-hull valve closed.

I got it to run, but noticed no water coming out the back end, so shut her down. checked out everything, started her again, still no water out the back end. Rebuilt the water pump, started her up, still no water.

I ran her for 2-3 minutes 5 or 6 times. I heard some loud knocking the last time i did it. THEN I FOUND THE ENGINE EXHAUST THROUGH HULL VALVE WAS CLOSED. Damn! I did not even know I had one.

I opened it, and -no problems, - I HOPE.

We motored and sailed her over to a new berth. She ran fine for at least 30 minutes, beginning and end of trip. Tied her up and headed home. Then got to thinking- could there be seawater in the oil? I mean, where did the exhaust and cooling water go while it was running??
I have not been back yet to check. But will do so as soon as possible.

Any advice for the new boat owner? Thank YOU
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Old 04-23-2011
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Bob,

Forgive me if I am telling you something you already know, but it sounds like you could benefit from a little tutorial on Engine Cooling 101.

I am not personally familiar with your engine. But I assume it is what we call "fresh water cooled".* This means that the engine has a closed cooling system, like your automobile, which circulates coolant (usually antifreeze) around the engine block to take away the residual heat from combustion. This is the "fresh water" part of your cooling system (again, usually using antifreeze instead of water).

The coolant is then itself cooled by passing it through tubes in the heat exchanger. The heat exchanger uses "raw" water taken from outside the boat, which is also pumped through the heat exchanger, but in parallel conduits to those through which the "fresh" side of the system passes. In other words, the "fresh" and "raw" water passing through the heat exchanger do not mix in any way.

As they both pass through the heat exchanger, the "raw" water sucks the heat away from the "fresh" coolant system. The cooled "fresh" fluid then gets pumped back to the engine block to grab more heat from it. The now hot "raw" water gets pumped out of the boat and discharged out the tail pipe with the exhaust gases from combustion.

Quote:
Then got to thinking- could there be seawater in the oil? I mean, where did the exhaust and cooling water go while it was running??
In your case, when you neglected to open the raw water thru-hull, the heat exchanging process never occurred. So there was never any "cooling water" that went anywhere. Your "fresh" cooling system (antifreeze) simply continuously recirculated in the closed system as it normally does. The exhaust gases from combustion would have discharged out the tailpipe, again as they normally do (albeit more loudly, for sure, since the waterlift muffler system uses the raw water to mix with the exhaust and thereby both cool and muffle it.)

While it's not good to run the engine with the intake thru-hull closed, my hunch is that your operation times were very brief and you probably did not overheat the engine. The run over to your new slip suggests things are okay. But do take a good look at your engine oil. If it looks like you have any milky water in it, you'll need to inspect further and maybe get some expert help.



*There is another, less common, form of cooling called "raw water cooled". In this system, there is no heat exchanger and no anti-freeze is used. Instead, raw water is taken in from outside the boat, pumped through the veins in the engine block, then mixed with the exhaust gases and discharged overboard.
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Old 04-23-2011
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Deadheaded my diesel

John,

Thanks for the info. I think you misunderstood. It was the outgoing valve, not the seawater intake that was closed.
What I do not yet understand was, did I only block the sea water from exiting, or did I block the seawater and exhaust from exiting? If I only blocked the former, I doubt I have caused serious trouble. I hope this is what happenedas I do not see how the engine could operate with the exhaust plugged. If I plugged up the latter, Which might be the case, I am afraid sea water could possibly back into the engine via the exhaust valves.

I will certainly look for any emulsion in the engine oil. Any other possibilities or problems I could have caused?

Any ideas? And I do appreciate the help.
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Old 04-23-2011
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Okay, Bob, I think I see what you're saying now. You have a thru-hull/seacock, where the engine exhaust hose exits the hull? And this was closed while you were operating the engine?

If I understand correctly, then what you have is very unusual, in my experience. I have only seen it once before, on a Crealock 31.

I don't think having that seacock closed would prevent raw water from being pumped into the heat exchanger. It would only prevent it from being discharged out the exhaust. I think what would happen is the water lift muffler would gradually fill up, until either the engine stalled from suffocation/backpressure (unexpelled exhaust gas), or the raw water backed up into the cylinder head. It's hard to say what happened in your case, but it definitely bears further examination.

By the way, the reason for the seacock is to prevent large following seas from back-flooding the exhaust system, where there is a concern that the loop will be insufficient. I view these with a suspicious eye, because the risk of operating the engine with it closed seems every bit as problematic as back-flooding from large seas. I would only close such a valve for long-term storage or severe conditions at sea. However, any time this seacock gets closed, the keys to start the engine should be hung from the seacock handle to prevent engine operation without opening the seacock.
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Last edited by JohnRPollard; 04-23-2011 at 03:00 PM. Reason: removed hyphen from "seacock"
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Old 04-23-2011
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HI John,

Yes thanks. YOU can see why I am concerned. I still do not see how the engine could have operated without exhausting? I did not see or smell any fumes below?



I have a PS 37. Thank you for the help.
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Old 04-23-2011
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Bob,
Depending upon how long you ran the engine and how hot the exhaust was you may have damaged your water lift muffler. You may even have melted it in which case your exhaust water would have gone into the bilge.The other possibility is a melted hose at the mixing elbow with the same result in the bilge and a lot of soot in the engine compartment.
I think one or the other would occur before any engine damage resulted.

Good luck,
Dianne and Chuck Burke S/V NiftyNickers C37 #139
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Quote:
Originally Posted by boblivingston View Post
..I still do not see how the engine could have operated without exhausting? I did not see or smell any fumes below?

Yeah, that is a bit mysterious. But there is a fair bit of volume in the exhaust system, between the hoses, exhaust elbow, and water lift muffler. Still, the exhaust needs to displace the volume that's there. Could it be the thru-hull was not closed absolutely all the way, allowing pressurized gas to escape but not water?

Let's hear what others think. I tend to agree with Chuck, but the absence of any exhaust smell is what I find odd. Were you maybe congested?
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Old 04-23-2011
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choking a diesel

confused yes, congested , no

Mr. Nickers, I do not believe my bilge has pumped. Nor were there any fumes or soot indoors? I had the engine compartment open and was looking at all this time. I am not sure if I was venting any or partial or full exhaust. I believe I was not as we could not rev the engine.

If the engine oil is not emulsified, I believe I am not in trouble.

Mysterious craft these vessels.
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Old 04-23-2011
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Just to be clear, Bob was being "helped" by the idiot previous owner (me) at the time. I never used to close that thruhull on the exhaust, but becasue it was cited as being seized during the survey,I freed it up - and obviously left the silly thing closed.

Anyway, there were exhaust gases escaping - but clearly not enough and the engine was not able to run fast.

Unfortunately, the last attempt to get it going before we realized the real issue, ended with some pretty loud knocking from the engine and I think that's what Bob is concerned about. The knocking disappeared as soon as we opened the seacock.

Question: The possibility of back-flooding the exhaust as indicated by John, what's the danger? If it only fills the exhaust, what's the problem? Why have a seacock there? - or does the water from the following sea get further into the engine? If it filled the exhaust, wouldn't the gases from combustion push all water out?



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Old 04-23-2011
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bob, I think you need to investigate and check the exhaust system very carefully. Yes, an exhaust thru-hull is unusual. And no, if it is closed, your engine CANNOT RUN. No engine can run when the exhaust is blocked. Kids used to stuff a potato up the tailpipe of a car to block the exhaust and make the car stall out.

If your exhaust really was closed off, and the engine ran anyway, the only way that is possible is if the exhaust was forced out another way. If the valve is grossly defective, so the gas could force past it. Or if it burst some other fitting, and the exhaust was being pumped into the engine spaces--which you'd probably have noticed.

Either way, you really need to find out what was wrong, because it still is wrong, potentially a deadly exhaust leak. If the engine is running OK and there's no contamination in the oil, the engine is probably OK, but there's still a problem.

By the way--some folks make a habit of putting the engine key on a strong, literally ON the water intake valve, so they have to go to the valve to get the key, ensuring the valve is opened before they start up the engine. In your case...it might be worth putting the key on the exhaust valve, when and if that is ever shut down on purpose.
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