Yanmar 4JH3-TE brown exhaust after 9 months

[SaltyMetals]

I have the Yanmar 4JH3-TE (2,000hrs). Before stopping the engine i always let it tick over on idle so it can cool off. I recently started it after having left it for 9 months. When i started it (at first attempt) for the first two minutes the exhaust was dark brown with the usual amount of water in the exhaust. After that it cleared and ran perfectly smoothly as usual.

Would i be right in thinking that the brown colour must have been the result of some corrosion in the cylinders? If so what is the recommendation for long term shut-down in the future? I read somewhere that something like WD40 is not recommended to spray into the air intake since this will wash the engine oil off the cylinder walls.

I suppose i should have kept a finger on the STOP button for a while to get the oil circulating before allowing the engine to start but it is too late for that this time. My boat is in the Med and an area where it will not suffer from freezing in the winter.

So what do you guys think caused the initial brown exhaust? I did a search in previous posts but could not find reports of this.
Your comments/advice would be greatly appreciated.

Andrew

[Wotname]

Likely to be corrosion in the exhaust mixing elbow getting cleared out.

Unlikely to be corrosion in the cylinders, that would be minimal and whatever might have there would have been scraped off by the rings in the first few revolutions i.e. in the first second or so.

[gonesail]

check the yanmar mixing elbow. my mechanic said this thing should be replaced at 600 hours

[SaltyMetals]

The mixing elbow looks v clean from the outside but as i understand it the problem that might occur is where the inner tubing is welded at the top and if that corrodes it will be inside the housing and unlikely to show outside. But no problem showing from outside. Will try and attach pic.

If yr mechanic is right that this should be replaced at 600 hrs then mine is long overdue (2,000 hrs). I see on the internet that it is poss to get a SS version. Would this not be better than an original Yanmar part?
Andrew

[SaltyMetals]

Sorry,for some reason the pic got rotated by 90 deg.

Maybe this will work
Andrew

[Bellinghamster]

Brown smoke or brown water? If brown water, then yes, a steel or iron component somewhere in the cooling water loop is corroding.

One really good thing to do before shutting down an engine to store it for any period of time is to flush the raw water cooling circuit with fresh water. Some people put a T in the sea water intake line, some run a hose into the top of the raw water strainer: connect a (fresh water) garden hose and shut off the intake seacock so your engine is sucking fresh water, run like that for 5 minutes or so to flush out all the salt water, then shut down and drain the water out (on a 4JH, remove the raw water pump cover). You should really also remove the impeller so it doesn't take a "set". Yanmar recommends plugging the air intake and exhaust outlets to prevent moisture ingress. Unfortunately, wrestling 3" exhaust hose on/off is never much fun. Might be easier to unbolt your riser elbow and cap the turbo outlet, which also give you a chance to inspect the elbow.

[Compass790]

Originally Posted by SaltyMetals

The mixing elbow looks v clean from the outside but as i understand it the problem that might occur is where the inner tubing is welded at the top and if that corrodes it will be inside the housing and unlikely to show outside. But no problem showing from outside. Will try and attach pic.

If yr mechanic is right that this should be replaced at 600 hrs then mine is long overdue (2,000 hrs). I see on the internet that it is poss to get a SS version. Would this not be better than an original Yanmar part?
Andrew

Whilst I'm not familiar with your engine I will say that ss is much better than cast-iron. Cheaper than the Yammer mafia too.Your exhaust elbow looks remarkably good for a 2000hr one. Doesnt look like cast-iron either.

Are you sure it hasnt been replaced before?

[Squanderbucks]

Typically most OEM and regular stock replacement elbows are cast iron. They are rather thick but continue to rust from the first time they come in contact with water (X10 for salt water).

If the boat were run every day the issue would not be so great. The culprit is Oxygen/Salt getting at the iron. Stainless steel custom exhausts are definitely better but they still have a useful life because the welds rust out.

Rule of thumb for most cast iron risers of good (not China cast iron) is about 4-5 years. SS probably 2 to 3 times that.

Fresh water flushing definitely helps with the risers and other components also.
The 600 hour number was probably chosen because the average recreational boater puts on around 100 hours per year. Not sure about you sailor guys.

I have the above mentioned "T" in my raw water hoses and flush when I return from a days boating if the boat is going to set more than a week before the next outing. Even with mine being SS.

Properly designed exhaust from engine to stern should not be causing any rust in the cylinders. If you can get exhaust water mist in your final segment of the exhaust where it connects to the engine then there is a design problem. These are very common and lead to early failures. A lot of the failures are when the first segment after the engine has the entire elbow covered with a water cooled jacket. The inner core rust out and water seeps back into the cylinders. Water should be introduced into the exhaust after the elbow and tubing are on the downhill portion of the system. Not at the top.

If I were going to have the boat on the hard for an extended period it might be worth it to fresh water flush, then"fog" with some oil spray the inside of the elbows and cap off the exhaust outlet. Belts and Suspenders approach.

[skipperpete]

Originally Posted by SaltyMetals

Sorry,for some reason the pic got rotated by 90 deg.



Maybe this will work

Andrew

Your mixer elbow is stainless steel and they do have about the life that Yanmar suggests but it is possible to re weld the inner sleeve where it attaches to the turbo face flange if you do it early enough. The danger with this design is that once it is corroded through it can in some instances dump a bit of water into the turbo on shutdown because the inner tube joint is right at the turbocharger gasket face.
To address your original question, if you have a metal aqualock, that is a good source for the rusty water and on occasion the reinforcing winding wire on the 75 mm exhaust can corrode to a remarkable extent but any ferrous metal anywhere inside in the raw water cooling circuit can do it.
If you can see a line of corrosion on the mixer elbow gasket where it contacts the turbo scroll (or worse.... where the turbo bolts onto the exhaust manifold) you have a problem ....and from you photo there is already a leak judging by the corrosion on the engine mount adjusting bolt.
Having missed his earlier post, I totally agree with Bellinghamsters suggestions.
Pete

[Compass790]

Originally Posted by skipperpete

Your mixer elbow is stainless steel and they do have about the life that Yanmar suggests but it is possible to re weld the inner sleeve where it attaches to the turbo face flange if you do it early enough. The danger with this design is that once it is corroded through it can in some instances dump a bit of water into the turbo on shutdown because the inner tube joint is right at the turbocharger gasket face.
To address your original question, if you have a metal aqualock, that is a good source for the rusty water and on occasion the reinforcing winding wire on the 75 mm exhaust can corrode to a remarkable extent but any ferrous metal anywhere inside in the raw water cooling circuit can do it.
If you can see a line of corrosion on the mixer elbow gasket where it contacts the turbo scroll (or worse.... where the turbo bolts onto the exhaust manifold) you have a problem ....and from you photo there is already a leak judging by the corrosion on the engine mount adjusting bolt.
Having missed his earlier post, I totally agree with Bellinghamsters suggestions.
Pete

Skipperpete, a question for you, is the inner sleeve pipe or tube on the yanmar elbow? Just curious as if I was fabbing one I'd definitely make out of sched 10.

[skipperpete]

Hi Compass790, the inner sleeve is only thin wall tube and the stubby little injection pipe goes into the void between the inner and outer tubes. It’s a really bad engineering design because a failure of that weld on the flange has serious consequences especially on the non turbo engines. Here’s a pic of 2 Yanmar turbo’s that were victims of the bad design from a pair of gensets mounted high above water level in a powerboat engine room so this water definitely came from the mixer failures.

[Compass790]

Originally Posted by skipperpete

Hi Compass790, the inner sleeve is only thin wall tube and the stubby little injection pipe goes into the void between the inner and outer tubes. It’s a really bad engineering design because a failure of that weld on the flange has serious consequences especially on the non turbo engines. Here’s a pic of 2 Yanmar turbo’s that were victims of the bad design from a pair of gensets mounted high above water level in a powerboat engine room so this water definitely came from the mixer failures. Attachment 242298Attachment 242299

Thanks for reply Skipperpete,Yea thats what i suspected it would be, tube. I always think dumb, dumb,dumb when I look at some of the Yanmar exhaust elbow designs but maybe its a cunning plan. Hey Yanmar get to sell more engine parts & turbos.
as well as exhaust elbows.

[SaltyMetals]

Skipperpete (#9), yes i thought my elbow is either Al or SS. Does not look like cast iron. The boat is 2004 and i bought it in 2016. Have no idea if previous owner had the elbow changed but when i bought the boat the engine had only done 700 hrs.

I am also puzzled by the rust on the engine mounting bracket ( good of you to spot it) but it looks like it might have come from the joint where the water inputs to the elbow. For some reason that joint only has one jubilee clip and you can see historical dribble marks from the joint.

Thanks to all the rest of you for the suggestions. It was not my intention to leave the boat for so long but Covid regs made travelling difficult. Good idea to make a fresh-water flush before leaving the boat. Will do that next time.
Andrew

[skipperpete]

Saltymetals, that’s another design deficiency from Yanmar on the mixer elbow...... there is barely enough length on the injection point pipe to get one jubilee clip on, let alone 2. AND it’s a perfectly smooth pipe, no barb or sealing flare.
Pete.

[SaltyMetals]

Pete,
I found a magnet. The elbow on my Yanmar is not magnetic which suggests you are right that the previous owner had it changed.. So, while it looks like cast Al to me it might be SS.

Either way , i am going to see if i can get anothrr jubilee clip on to that hose which appears to have been leeking. I am aware of the problem of putting a jubilee clip where it might be near the edge of the pipe so might just end up tightening the existing.

Many tks for all suggestions.
Andrew