Yanmar 3GM30F exhaust water plumbing

Engines, Drive trains, Propellers, Steering, Ground Tackle and other mechanical system

Yanmar 3GM30F exhaust water plumbing

Postby RadioZephyr » Tue Jul 11, 2017 9:07 am

I was running my engine at the dock yesterday, and a neighbor pointed out that water was exiting in two different places: the exhaust port, and what turned out to be the port side cockpit drain. I had never noticed this before. I soon discovered that the hose that runs from the seawater outlet on the heat exchanger to the mixing elbow has a T in it, with a hose that runs back through the cockpit locker to the top of the port side cockpit drain.

From what I can tell, Yanmar's design has the hose going straight from the heat exchanger to the exhaust elbow. I had always assumed that hose was a siphon break or something, but it doesn't make much sense if it's filled with engine water. Does anyone else have this on their engine?

Elbow.png
from Yanmar parts catalog
Elbow.png (182.61 KiB) Viewed 492 times


Hose in engine compartment.jpg
Hose in engine compartment.jpg (228.6 KiB) Viewed 492 times
Josh
F36/38, Hull #25
Boston, MA
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Re: Yanmar 3GM30F exhaust water plumbing

Postby rafontaine1 » Tue Jul 11, 2017 12:50 pm

Yes I have a similar arrangement on my 36 except the tee is much further up under the engine compartment and the hose and fitting going to the cockpit drain is much smaller. Always thought of it as a siphon break and never really got a lot of water out of it. If you think about it it is a good check on the exhaust elbow ability to pass water. The more restriction in the exhaust elbow the more water discharged out the tee. When was the last time the exhaust elbow was replaced? FYI - because you are pumping water out the exhaust is not necessarily an indication your exhaust elbow is good. I found that out this year when out of principle I replaced mine. The water passage was completely clear but the engine exhaust passage was so blocked I could just about see light passing though it. A quarter inch thick rod wouldn't even pass through. Mine was the original from 1986.
Rich Fontaine
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Re: Yanmar 3GM30F exhaust water plumbing

Postby RadioZephyr » Wed Jul 12, 2017 8:47 am

Hey Rich,

Glad to hear I'm not the only one with this setup! As you can see in the picture, the screw that's supposed to be supporting the T connector isn't actually screwed into anything, so it's just been hanging there for a while (at least since I bought the boat). Last night I mounted the T connector as high on the wall as it would go, but as you can see from the attached photo, water was still going through it. The mixing elbow looks pretty new, so I've always assumed it was recently replaced. I won't know for sure until I crack it open and take a look :(
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Josh
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Re: Yanmar 3GM30F exhaust water plumbing

Postby Salacia » Sat Jul 15, 2017 2:48 pm

Josh,
We met at the marine store earlier this week. I told a mechanic about your exhaust. He said direct drive engines stream exhaust water thru the prop below water and have a small 'tell tale' stream to let the captain know the exhaust is pumping. That seems to be w hat you have. Your engine was probably intended for a direct drive installation and somehow goto redirected.
If it is annoying, change the elbow. You will need to one of these years anyway.
best of luck,
Stephen Lee
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Re: Yanmar 3GM30F exhaust water plumbing

Postby RadioZephyr » Wed Jul 19, 2017 3:27 pm

Hey Stephen,

Good meeting you the other day! I'm a little skeptical, because I can't imagine how exhaust water could be streaming through my prop. It also doesn't seem like it would be a "telltale," as the outgoing water can't be seen from the cockpit. The main exhaust hose is routed to the port side by the waterline, just aft of the wheel, and it can be observed by looking over the side.

I'm planning to replace the exhaust elbow (eventually), and I guess I'll see what it looks like at that point.
Josh
F36/38, Hull #25
Boston, MA
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Re: Yanmar 3GM30F exhaust water plumbing

Postby Salacia » Thu Jul 20, 2017 8:46 am

What I was trying to say is direct drivie or sail drive systems exhaust thru the prop. We do not have sail drive systems. That is why there is confusion on your exhaust. Your engine was originally built for a sail drive boat and got redirected at TPI, where Freedoms were built.
If still confused, give me a call.
Stephen
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Re: Yanmar 3GM30F exhaust water plumbing

Postby Salacia » Thu Jul 20, 2017 8:46 am

What I was trying to say is direct drivie or sail drive systems exhaust thru the prop. We do not have sail drive systems. That is why there is confusion on your exhaust. Your engine was originally built for a sail drive boat and got redirected at TPI, where Freedoms were built.
If still confused, give me a call.
Stephen
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Re: Yanmar 3GM30F exhaust water plumbing

Postby RadioZephyr » Thu Jul 20, 2017 9:02 am

Ahh, ok. I'll have to look into that.
Josh
F36/38, Hull #25
Boston, MA
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