Raw water cooled issues? - SailNet Community
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post #1 of 6 Old 11-08-2009 Thread Starter
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Raw water cooled issues?

I have only had experience with fresh water cooled engines but am now looking at a 2QM20H.

How do you survey a raw water cooled engine?
What parts need to be replaced and or serviced on a regular basis?
How do you tell it if is shot or nearly shot?
What exactly kills this engine?

In other words whats the probability of happiness with an old raw water cooled engine.
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post #2 of 6 Old 11-08-2009
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I have owned my first water cooled Yanmar 2QM20H for just one year. People have told me that they are a great engine - "almost bullet proof" was one comment.

Because we were taking her 1000 nautical miles, I wanted to have it checked over and get a few things done first. The survey said to replace the stuffing box hose and suggested that we replace the engine mounts. (I was later told that that surveyor always says to replace the engine mounts).

We opted for replacing the stuffing box hose, BUT - the mechanic could not get the shaft off the shaft coupling. Long story short - had to pull the engine to replace that hose. While pulled, I had him replace the mounts. Also replaced the impeller and the zincs. (Doing the impeller and zincs were so easy it will be an annual thing for me now). I did both fuel filters and found a problem with the external fuel pump and replace that as well.

All in all, about $!200 in parts and labour.

But, we started her up and she ran like a top for 1002 miles home. No problems (other than changing the external fuel filter, for the rest of the summer either. She burns less than a 1/2 gal per hour at 2500 RPMs at hull speed and we are really pleased.

I am considering putting on a heat exchanger (to make her fresh water cooled and to increase the temperature of the liquid going through the domestic water heater). But the jury is still out on that job.

Access is good and she is a pretty simple engine.

That's my limited experience two cents worth.


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post #3 of 6 Old 11-10-2009
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- - In another thread the subject was discussed, but the main problem/consideration with raw water cooled engines these days is pollution and mud in the sea water. Since the engine on small sailboats is normally run to exit and enter harbors, all the dissolved stuff like mud and chemicals is circulating and being deposited inside the galleries of the engine. Calcium build ups from microscopic sea life getting cooked is also a potential problem.
- - Fresh water cooled closed circuit systems do not have to worry about these considerations. Converting to a closed circuit fresh water cooled can be simple or complex depending upon the engine and the available room around the engine. If getting a new engine - fresh water cooled is preferable - if - it will fit into the area you have available.
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post #4 of 6 Old 11-10-2009
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On the boat i sail on with a 1981 diesel it just slowly rusted enough to start putting water in the oil so they did a LOT of oil changes and repowered over the winter

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post #5 of 6 Old 11-10-2009 Thread Starter
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Is it possible to flush the engine somehow to clear out the deposits.
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post #6 of 6 Old 11-10-2009
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A vinegar flush of the raw water cooling system or even stronger acid like muriatiatic acid flush should do the trick. A nice weak acid like vinegar (acetic acid) should be done annually. Not really a big deal for the environment or you.
Note to self: flush raw water cooling system with WHITE vinegar before the snowflakes start coming down.
It is also possible to install a heat exchanger (HX) on a raw water cooled engine IF it is not too old or long lived in salt water. Don Moyer has a heat exchanger kit that works for the A4 but like everything else in boating it is not cheap.
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Last edited by CalebD; 11-10-2009 at 09:22 PM. Reason: more
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