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morgantheship 11-16-2008 10:41 PM

Raw Water Cooling System Questions
I am in the process of repowering my Hunter 27. It currently has a Renault engine which I will be replacing with a Yanmar 2GM engine. Yesterday I disconnected everything from the Renault engine in preparation of pulling it out of the boat. Let me prefice that there are two seacocks. One for inlet water and one (I thought) for outlet water. I noticed that only the inlet water cooling water line was connected to the engine. And the outlet water line ran somewhere else but was not connected to the engine. So I began to wonder what the outlet water line is connected to and what is the purpose of the outlet water line and its seacock?

The Yanmar 2GM engine that I will be installing is also a raw water cooled engine and I am wondering if it also will be connected the same way?

Could someone enlighten me with some understanding as to how this cooling system works and what I might need to pay attention to when installing the Yanmar engine? Thanks.

ckgreenman 11-16-2008 10:56 PM

I can't speak for sure on diesels but I know most raw water cooled gas engines expel the water through the exhaust manifolds. My gues on the other seacock is that it is an inlet for some other system.

sailingdog 11-16-2008 10:56 PM

The cooling water probably goes from the engine to the waterlift muffler and then exits with the exhaust out the transom of the boat.

The other seacock may be for a salt water washdown system, a salt water galley faucet, the reverse cycle A/C system, transom salt water shower, or a watermaker if you have one.

camaraderie 11-16-2008 11:19 PM

...or the head!

scottyt 11-16-2008 11:27 PM

my 83 hunter 27 has the water intake right under the engine (yanmar 1gm) the only other thru hull in the area is the sink and its under the cockpit. i would think someone added one for something else, or maybe added a new one for a strainer instead of messing with the old thru hull

Faster 11-16-2008 11:44 PM

On these engines the cooling water goes into a mixing elbow at the back of the exhaust manifold, then the exhaust and water go to the muffler after which it's expelled with the exhaust.

btw if this is a used engine you're installing it's worth checking the condition of that mixing elbow now. This is an area that is prone to corrosion and failure (esp if it's been in salt water)

If there's a line coming from your "extra" seacock, now's the time to figure out where it goes and what its for!

sailingdog 11-16-2008 11:58 PM

It would also be worth re-bedding the through-hulls and making sure they're properly potted if you have a cored hull. :)

Rockter 11-17-2008 05:27 AM

What about a picture or two?

ckgreenman 11-17-2008 11:10 AM


Originally Posted by camaraderie (Post 403088)
...or the head!

This was my thought. If the boat is equipped with a true marine head it's probably pulling raw water as well.

morgantheship 11-17-2008 01:30 PM

I will be at the boat on Wednesday when the yard helps me pull the engine. I will take some pictures and post them.

At this point I realize that I didn't know much about the seacocks. When I purchased the boat, I was instructed to open these two seacocks prior to starting the engine and then to close them when finished. Never looked at routing or what they went to. Guess its about time I find out more about what lurks in the dark corners.

I do know now that only the first seacock is the raw water inlet and I now understand that the water circulates in the engine and exits via the exhaust.

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