Exhaust Mixing Elbow Inspections

[Dreaming Yachtsman]

Today I replaced the exhaust mixing elbow on one of my Yanmar 3GM30-FC engines. The old elbow was only five years old but had developed a crack in the external weld between the outer sleeve and the flange that bolts to the exhaust manifold. A local mechanic at Bahia del Sol, El Salvador, ruined the piece when he welded a bead all the way around the outer pipe to stop the leak - the heat from the weld warped the flange and opened up the seam between the inner and outer sleeves. After a stutter step trying to get a new elbow through an El Salvador company, I gave up and ordered one from the U.S. The part arrived four days later on DHL but took another four days to get through customs. Close examination of the old elbow revealed pits on the inside of the inner sleeve that look like they are nearly half way through the wall thickness. The exhaust line was pretty heavily caked with carbon build up as well.

My questions:
1. Does anyone know the recommended frequency for inspecting the elbows for internal pitting? The owner's manual does not specifically address the issue but one could argue that such an inspection would be included in the cleaning specified every 300 hours. I just don't like breaking open perfectly good joints for no good reason.

2. Will the carbon deposits now in the exhaust manifold eventually burn out if I run the engine more heavily loaded than I have been? We have in the past cruised on both engines at about 2000 RPM for fuel economy but have recently started running only one engine at 2600 RPM, the cruising speed listed in the boat owner's manual, not the engine manual. Max RPM listed in the boat owner's manual is 3600.

[maxingout]

In an eleven year circumnavigation, I replaced my exhaust elbows two times on my Yanmar 3GM30F. The first time was in New Zealand, and the second time was in Cyprus. They both rotted out from the inside.

I tried patching them up, but was never successful. Plus there's the problem of flooding the engine room with exhaust cooling water or toxic carbon monoxide if one of the exhaust elbows fail after patches are made.

I regard exhaust elbows as disposable items that are not to be patched. They are easy to replace and trouble free until they fail.

[Ex-Calif]

My experience on welding exhaust system components is that you need some pretty good cleaning tanks to remove the chemicals imbeded in the metals pits. Otherwise the weld becomes contaminated and the joint fails. I'm talking professional type hot acid tanks.

To your other question about how hard to run the engines, 2,000 seems awfully low for a 3600 RPM redline. 2600 seems much better. Have you run the boat with both engines at WOT? What RPM tdo you get?

[delmarrey]

In response to post 1 & 2, I think it would be wise for Yanmar 3GM30F owners to carry an extra elbow, or two.

And DY, I think I'd be looking over the other one real good before anymore future long voyages.

It's common knowledge here, at least where I've always churned the waters, that one should not attempt to weld exhaust castings, even on cars. Every dealership will highly recommend a replacement.

[Dreaming Yachtsman]

Maxingout,
I have come to the same conclusion you have: exhaust mixing elbows are consumable items. I only wish the owner's manual or some other document had made that clear to me before I left on a long cruise. I will have to stock up at the next opportunity.

Ex-Calif,
I have not pushed the throttles to the limit of their movement so I don't know exactly what full speed is. I always watch the tachometer to be sure I don't exceed max rated RPM. However, my wife may have exceeded the limit once while trying to regain control of the boat after having dragged anchor, bounced off another nearby boat, and rapidly approached rocks on the shore. I'm sure she didn't care what the tachometer read, though, even if she had taken the time to look.

delmarrey,
I didn't really expect the weld repair to work but figured it was worth a try while waiting for two new factory replacements to arrive. I now have a spare for the port engine.

[Roy M]

Next question: Where is the cheapest place to get exhaust elbows for the Yanmar 3GM30F? Dealer prices are nasty.

[CS27]

Being penny wise and pound foolish, I tried to clean a 4 year old mixing elbow and an 8 year old exhaust elbow (I've been told that Yanmar says the mixing elbows have an 8 year life span with the exhaust elbows being longer). Long story short, a local transmission shop soaked them in solvent overnight and ran them several times through their steam cleaner/soak tank. They came out quite clean and the shop even refused to accept any payment, but being too stupid to leave well enough alone and knowing that "the enemy of good is better" I tried to make them 'better' by soaking them in 5% muriatic acid which cleaned them well, but also removed all the outside paint and started an internal and external rusting process that is challening to reverse. I treated them with an anti rust compound that quickly burnt off (stinking up the cabin in the process) after they were reinstalled... evidently Ospho phos. acid would both treat the rust and tolerate the high temps so now I get to re & re everything again. After all this messing around including removing seized bolts and fighting an exhaust hose that melted onto the mixing elbow (tapping a long thin flathead screwdriver between the hose and the elbow was the only way to get them apart), I would strongly advise people to replace the mixing elbow every 8+/- years and forget about trying for a cheap fix when they do fail.

Best prices I could find were at:

http://www.bluewatershipsstore.com/E...nmarparts.aspx

and

http://shop.torresen.com/ships_store/

[FloridaWriter]

Originally Posted by maxingout

In an eleven year circumnavigation, I replaced my exhaust elbows two times on my Yanmar 3GM30F. The first time was in New Zealand, and the second time was in Cyprus. They both rotted out from the inside.

I tried patching them up, but was never successful. Plus there's the problem of flooding the engine room with exhaust cooling water or toxic carbon monoxide if one of the exhaust elbows fail after patches are made.

I regard exhaust elbows as disposable items that are not to be patched. They are easy to replace and trouble free until they fail.

Mastry Marine in St Pete recommends replacing the elbow on the 3GM30F every 5 years, so that would be about right.

[john540]

On my Westerbeke W70, I was getting a significant amount of smoke in the cabin. I discovered that it was coming from the exhaust elbow. I don't have any idea how old the elbow was. I replaced it with a new Westerbeke elbow, and the new paint burnt off almost immediately. I also broke a stud trying to get the rusted nuts off, and another stud unscrewed instead of the nut unscrewing. After reading this thread, I think I'll purchase an elbow or two to have in my spares kit.

[s/v Jedi]

I've read somewhere in an owners- or service-manual to remove, inspect and clean them every 600 hours. We do this for the genset (in 7 years we didn't even put 600 hours on the main engine...). We just replace the elbow with the spare, replace the gasket if it's damaged and use Permatex gasket dressing on it to prevent gasket damage the next time (works!). When genset is up and running again, we clean the removed elbow and if it's still okay, it becomes the spare.

We do this maintenance at the same time we clean the heat exchanger, have injectors tested etc.

About the hose: we finally gave in and replaced the small piece of hose between injection elbow and waterlift with that expensive corrugated silicone exhaust hose. We've been promised this doesn't harden like the regular hose so it should be easy to remove for maintenance without ruining it.

cheers,
Nick.

[Chief Engineer]

What's considered nasty?