3GMD dripping water on port side--engine shuts down

[2Sheets2TheWind]

We have a Yanmar 3GMD raw water cooled engine. Had only run it this season in the slip, and only for 5 or 10 minutes (weather has not been conducive for sailing). Twice I noticed the first few spurts of exhaust water just after the engine was running left a black cloud in the water behind the boat. Had the boat out of the slip and running. Was visually checking the engine while underway and my first mate at the helm. Noticed water dripping from the port side of the engine forward of the starter but behind the alternator, but could not tell where--the alternator blocks my view. Shortly after that, the engine shut down.


I have not done anything as of yet. My plan is to pull the waterpump and inspect to see if the impeller is intact. Next is to remove the alternator and view the area. I'll attempt to start the engine (without the seacock open). If it operates normally, I'll open the sea cock and let it run for a while to see if it leaks again.


Is there anyone who has encountered this, or nose the cooling system well on a Yanmar 3GMD that may have insight into the cause and fix?

[2Sheets2TheWind]

Update: I removed the waterpump and the impeller was intact. I went ahead and replaced it. I removed the alternator and took the pictures attached of the affected area. Several large chips flaked off. See pictures.

[TonyNA]

Appears to be a leaking freeze plug. Do you live where it gets cold enough to freeze? You'd need to drain all the cooling water, dig the plug out, clean up the opening and inspect so a new plug will no leak and press a new plug in. I have a raw water cooled 3QM30 but don't recall it having any freeze plugs but can take a look.

[2Sheets2TheWind]

Not really, Tony. It's Virginia Beach. I put the pink stuff in the engine every fall as well as one of those West Marine heaters set to come on when it gets below 38 in the engine room. I tell fellow boaters what I do and they say "why? It doesn't get that cold here." And it's definitely been colder in past winters than this last one. No ice formation in the marina. Is the attached the "freeze plug" you're talking about? Someone else called it a drain plug.

[SY Harmony]

Does the oil look like chocolate milk?

[TonyNA]

Hey Sheets, the part you have circled is valve you open to drain the water from the engine block. There is another one under the exhaust manifold as well. The freeze plug is the grey round shape in the middle of the rust section just to the left of the part you circled in the photo. They're called freeze plugs because they may save your engine block should the cooling water freeze and expand it will push the plug out and relieve the stress thus saving the block from cracking. Since yours didn't freeze it probably just started leaking due to GKW. They do occasionally start leaking for no apparent reason.

Here is some guidance on how to get the job done:

https://youtu.be/SrWozXoQnBI

Oh, I forgot to ask... did you shut the engine down or did it die on its own?

[2Sheets2TheWind]

Thanks, Tony. It died on it's own. What is GKW? And do you recommend I just replace the freeze plug even if the engine died on it's own? Thanks for the video.

[Wotname]

GKW = god knows what = who knows

[2Sheets2TheWind]

Thanks, Tony. Does the fact that it shut down on it's own mean anything?

[Wolfe10]

Remove more of the rust-- it is not holding anything together. Almost appears that there is a horizontal "rust source" above the freeze plug. ?Cracked block?

[TonyNA]

Originally Posted by 2Sheets2TheWind

Thanks, Tony. Does the fact that it shut down on it's own mean anything?

Difficult to say at this point but I don't think the water leak is related. It's bothersome that it quit running. Was it under load when it quit i.e. powering along at 1800+ rpm or idling along at 700 to 1000 rpm. If it dies under a decent load I'd check that fuel is getting to the injector pump by making sure the filters are clean.

The suggestion of clearing away the rust is a good one. I'd clean the area off and dry it and then try and pinpoint the source of the leak. You can run the engine with the alternator removed and view the suspect area.