Drowning Yanmar 3YM20

[Catalina Big Hook]

My second thread. Yee Haw.

Looking for someone with same engine as mine and the low rise exhaust/salt water mixing elbow.

Have to shut off the seacock to keep my diesel from drowning.
I have found out that the plumbing (among other things) was modified by someone who was using the boat with intent to buy, and did a whole bunch of work to it, then backed out.

It's my boat now, and the very first time I took her out, she filled one piston with salt water. I got her bled out and running within an hour.

It's a crime, because the top reason I bought this boat is the engine only has just over 100 hours on it and from all my research, salt water in the engine for 2 hours destroys the engine. Hopefully 1 hour didn't do (much) damage.

I figured out what is wrong, and I know how to fix it. However in all my research, I have come to the conclusion that even after correcting the plumbing so it doesn't siphon anymore, the Yanmar exhaust mixing elbow is a flawed design. (Quite common, as it turns out. Engine makers should stick to making engines is the consensus I've gotten).

The mixing elbow is an upside down U and the salt water should be injected into the U on the far side from the engine so that not just exhaust pressure, but also gravity ensures NO salt water can run back into the engine.

As it is, the salt water injection nipple is on the engine side of the elbow, so that the salt water has to go up and over, then down into the wet muffler.

This means that the instant the engine is shut off, any salt water that didn't make it over the hump and some in the line as the anti-siphon does it's thing, will run back into whatever exhaust valve(s) that are open. Every time.

The only thing I can see preventing that is if the mixing elbow is actually a pipe within a pipe, with the salt water pipe terminating AFTER going up and over the hump.

Can anyone tell me if this is so? Apparently the elbow needs to be replaced every 5 years or so as it is cast iron. So I'm thinking someone out there has seen the innards.

 

[Ed Schenck]

Wonder when they started using that elbow? I installed the 3YM30 myself and just kept the original exhaust. The elbow is like the 2QM, down at about 45 degrees. There is a big loop in the exhaust hose from the bottom of the pan to the underside of the cockpit sole. And just a straight through muffler. Never had problems with the original 2QM20 nor the new 3YM30.

 

[Old Skool Neil]

Big Hook,
I'm guessing Catalina 30? If so, there's another special little problem to consider. More later if that's the case.

And yes, those mixing elbows are typically water jacketed but once the water enters the exhaust pipe it has to naturally flow away from the engine or there's trouble for sure. Sounds like yours was modified by someone who didn't fully understand the concept.

 

[RichH]

If the injection elbow is LOWER than the waterline of the boat ... you ALWAYS will have the risk of 'back flooding'. This includes the dynamic water waterline when the boat is heeled. The engine manufacturers have no control over how much lower beneath the waterline or dynamic waterline an engine is installed.

If you have backflooding (not caused by a pin hole in the exhaust manifold - always a possibility), the ONLY way to solve this is to MODIFY the height that injection elbow is in relation to the waterline. The typical and easiest is a 'dry stack' arrangement made from common 'black iron piping' and which the cooling water from the exhaust header is bypassed around the 'dry stack riser' and connects (with vacuum breaker) to the now 'elevated' injection nozzle.
The problem with dry-stacks is they can only be insulated with 'lagging', etc. and the heat transfer into the engine spaces is high, usually requiring a blower, etc. to get the heat from the 'dry stack' out of the engine compartment.
Every Yanmar dealer on the planet has the 'adapter flanges' to make a 'dry-stack' ... and usually will supply the common Westerbeake Aluminum injection nozzle that simply 'screws onto' the terminal section of the 'dry stack', you have to supply a bronze, etc. 'vacuum breaker' for the extended manifold to water injection hose, plus you will invariably need to 'lengthen' the rubber exhaust hose to the water lift muffler.

If the exhaust injection nozzle is BELOW the maximum dynamic waterline you WILL ruin an engine.

 

[Don12364]

Big Hook,
I feel you must be mistaken. On other Yanmar engines, whilst the water injection nipple is on the manifold side of the 'U' bend, the actual point where the water enters the exhaust is on the muffler side. i.e. beyond the high point.
This way Yanmar are able to water cool most of the U bend and particularly the crest of the bend so that it is non lethal as far as burns go.
Suggest you look inside your bend.
Is it original? Can you get a proper exhust riser into the space - and a siphon breaker?

As RichH said, if the elbow is below waterline you will always be vulnerable to flooding via any leakage through the raw water pump.
This is not siphoning but rather a direct feed and the only solution would be to close the Kingston cock every time the engine is shut down. Perhaps even fit a motorised valve off the ignition circuit.

 

[Old Skool Neil]

Rich,
Not trying to be contrary or rude, honestly, but the Catalina 30 riser height is limited by cabinetry and seating to a maximum height approximately equal to the static waterline. Further, the waterlift is mounted to port of the engine so port tack elevates it. Add the lengthy exhaust hose run to the transom with expected backwash into the waterlift upon shutdown and the rather smallish waterlifts in the early boats and you have the perfect storm of conditions for a potential engine flood.

And this isn't unique to a particular engine. It's the case for A-4's and a variety of diesels found in that model. Yet, with somewhere around 6500- - 7000 boats built, reports of flooding are rare. Not unheard of but rare. Unfortunately, it's the hand we are dealt. Big Hook's issue is compounded by the P.O.'s exhaust modifications but even when it's straightened out he hasn't reached Nirvana. BTW, I noticed he posted on the Catalina 30 category so I figured that's what he has.

I haven't flooded mine but I'm not waiting until I do. I'm working on an automatic system that evacuates the water from the muffler each time the engine is shut down. It's in the concept phase right now but I may have a working prototype installed over the winter. For us C-30 guys, it's one more layer of protection.

 

[s sauer]

Yanmar Mixing elbows

I have a Yanmar 2GM20F with that 'upside down U' and I've taken it apart and cleaned it so I do know that there are two separate chambers in the casting; HOWEVER, the Seloc yanmar engine manual specifically shows an injection elbow of this type that had corroded thru the parallel chambers and would do exactly what you are describing. On our Hunter 28.5 this injection elbow is above the static and dynamic waterline.

 

[AtlanticAl]

I had the same problem on an irwin citation 35, with a yanmar, and an exhaust like you describe. The way to solve it, is by adding a breather to the top of the upside down U, I cant remeber the full details of what you have to do, the book i had explained it quite well. The previous owner never needed to do it, as he didnt take the boat into heavy weather, i took it to Bermuda in December, and the engine filled with water. I havent heard anything about salt water destroying the engine after a few hours, and i just cant imagine it would, their is no oxygen inside and engine, so it wont rust quickly, and even though it is salt water, its not in any way abrasive, I just changed the oil a couple of times, and it was good as new, apart from the bent push rods, due to the idiot that was with me, not being able to follow instructions, i told him, never start the engine without opening the decomprssion leavers, i would open three, then turn the engine, and drop each leaver one by one, he was too lazy, so he bent the push rods, you cant compress water.

 

[kloudie1]

Drowning Yanmar

Catalina.. here is a shot of the elbow on the Yanmar 3GMF.. the water injection point is on the "uphill" side but as others have noted, there is a water jacket thet contains the water around the top and the internal opening is on the "downhill" side.. The other picture shows the anti-syphon loop in the cooling line after the engine and before the exhaust ell. It is the little stainless loop on the aft of the engine box, higher than the exhaust ell. There is also a high loop in the exhaust hose itself after the muffler . In the Cat 30, could the anti syphon loop be up under the sink?

 

[Catalina Big Hook]

Re: Drowning Yanmar

Thanks everybody.