Yanmar 6LY main heat exchanger color

[David Marchand]

Please look at the attached photo. I am helping a friend who is considering buying a 2006 Mainship Pilot 34 with a Yanmar 6LY 370 hp engine. A “Yanmar Certified Technician” who was present at the seatrial said that the main heat exchanger, which is very visible in this pic, is discolored and is a sign of severe overheating. Well the color is certainly not the Yanmar silver grey, but it is entirely uniform and doesn’t look like it was caused by overheating to me. And how does the outside which is on the coolant side get so hot unless there was a total loss of r/w flow, the coolant all boiled out, the exhaust manifold got real hot and caused the main heat exchanger to get very hot. That would probably be a catastrophic situation.

My guess is that it is just an anodizing coating from the original casting manufacturer and may not be a genuine Yanmar part, which brings up another whole set of questions.

Any ideas?

David

Topic

[Tony Athens]

I wish I had a much better picture so I could really “SEE”, but even a “fuzzy” view tells me that this engine, when it ran or did run, is being squeezed to the max, plus the signs of a loss of coolant in the combo exhaust manifold/coolant tank are more than obvious…………..Walk away unless someone gets a $25-30K concession on the $$..

The 6LYA is a very good engine, and IMO, is as good as a 370 Diamond in many ways, but it is not forgiving, nor can it be “fixed” cost effectively when it’s abused to where it needs a rebuild.

Tony

[Rob Schepis]

Good advise, only better advise might be to tell him to run, not walk!

Yup, the fact that it overheated on the sea trials tells a lot..

[David Marchand]

Rob:

I don’t know much of the story, but here is what I do know as related to me by my friend:

On the first sea trial the engine over heated immediately and they immediately returned to the dock. That engine has a three way valve on the sea side of the strainer (so you can use the r/w pump as an emergency bilge pump) and it apparently was partially closed. Later it was opened or so my friend believes as the handle is very loose and sloppy and just setting it at 90 or 180 degrees doesn’t tell you much and no one seems to know to look at the stem position.

But anyway another sea trial was done and it also over heated but not as badly. As far as my friend knows there was no significant work done as a result of prior over heating events, but who knows for sure.

Given the prior over heating event that caused the bronzing of the casting and the over heating at the sea trials it does seem like a comedy of errors and perhaps deceit. At this point I would counsel my friend to not believe anything other than what he can verify with his own eyes or with trusted pros. Based on your advice I now have more confidence in the Yanmar technician he hired to make the second sea trial who identified gross prior over heating due to the casting’s bronze color.

At this point I am suspicious of the whole deal and have advised my friend to walk away. There is more wrong with the boat than just the engine: all port lights leak, the prop cavitates badly, etc.

David

[Rob Schepis]

David,

Are we sure the engine was not damaged and subsequently repaired at some point in it’s history?

[David Marchand]

Reply to Tom

Tom:

I totally agree. I advised my fellow boaters with the same boat and engine as mine to replace the injection elbow every ten years. But did anyone listen?

David

[firehoser75]

David,
Don’t let the fact that the exhaust elbow is made of stainless steel give you a false sense of security. My Cummins (stainless steel elbow) rotted through last year (15 years old) and if not for my exhaust hose temperature alarm we could have suffered major damage. Luckily, we caught it in time.
I too have been trying to bring the issue to people’s attention on various forums, and have a few Cummins owners make changes as a result.
Regards,
Tom

[David Marchand]

Reply to Rob and Steve

Thanks Rob and Steve for your replies.

Rob: Sorry I misspoke, that is the coolant tank and I had forgotten that it is integral with the exhaust manifold. That and the uniform bronze color of the turbo housing that you showed does indicate that it was BBQd as you say at some point. If it were caused by r/w failure that boiled all of the coolant out suddenly wouldn’t that melt the exhaust hoses, lift muffler, toast the turbo, and lots of other catastrophic issues. If it were caused just by loss of coolant wouldn’t it blow the head gasket, warp the head,…..

Steve: I am quite familiar with that engine and its installation on the Pilot 34 and you are right, it is doomed to fail, not to mention the riser being only 8″ above the water line. I fixed both of these issues on my boat by increasing the riser height to 16″ and rotated the mixer downwards so it is self draining. For several years I was on a crusade to let other Pilot 34 owners know of this risk but I think only a few have done anything about it. Fortunately the Yanmar mixer is stainless steel so it has less risk of corroding out and the riser height apparently doesn’t often cause problems.

David

[Steve Lewis]

Yanmar Exhaust Config

David and Rob,

Is that a wet elbow coming out of the turbo that is oriented incorrectly and comes under the heading of Doomed to fail? or is the picture angle skewed so that the exhaust is properly configured?

Steve

[Rob Schepis]

Hello David. When you see the “bronze” color on a grey Yanmar that is the same as the “burnt brown” on a white Cummins – HEAT. See my pic – Here’s a “bronzed” turbo on a 6LY that I inspected. I explained”overloading” to the owner but it went on deaf ears and the engine ate a valve the following season.

By heat exchanger I guess you mean the fresh water (coolant) tank? The fresh water tank is integral to the exhaust manifold (one big casting) so that would explain the heat. I think the tech was on the right track and this engine was BBQ’d at some point in history

[Author]

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