Oily deposit in exhaust manifold and mixing elbow- cause?

[Copacabana]

Background: Over the last two years or so, I've noticed my Yanmar 3GM30F engine does not get up to cruising revs as it had in the past. At around 2,300 RPM, I start getting brownish smoke and can't get the engine to go above 2,500 RPM. No smoke at 2,100 RPM. This problem has been gradually getting worse. My first thought was the mixing elbow. I have already changed all the filters, painted the bottom and the prop is clean. The engine starts cold on the first crank in idle RPM and has normal water flow and clean fuel and air.

I took off the exhaust manifold to change the mixing elbow. The engine has 2,600 hours on it and had the original mixing elbow (yes, long overdue). I found an oily black sludge deposit in the exhaust manifold and elbow (photo). Not completely blocked, but restricted. I was expecting a hard, dry carbon buildup, not an oily tar. I sent the manifold to the local Yanmar shop to be cleaned and will reinstall it with the new elbow next week.

I asked the Yanmar guy if this buildup was enough to restrict the exhaust exit and reduce revs. He said it could be, but suggested that perhaps I had an injector that wasn’t spraying properly.

Is this oily black deposit normal over time? Could the oily aspect be from the unburnt fuel accumulating from the gradually restricting elbow? Should I look for another cause? Could it be a faulty injector?

Thanks in advance!

[Copacabana]

Manifold after cleaning and painted with primer

[a64pilot]

Yes, it could be from an injector.
Especially if your oil consumption is insignificant as in less than a quart every 100 hours, but if your burning oil as in say a quart every 25 hours or so, it’s likely oil.

[Copacabana]

Originally Posted by a64pilot

Yes, it could be from an injector.
Especially if your oil consumption is insignificant as in less than a quart every 100 hours, but if your burning oil as in say a quart every 25 hours or so, it’s likely oil.

I don't think I'm burning oil. I probably add less than a quart every 100 hours.

I was was wondering if a faulty injector would manifest itself as well at lower RPM and when cold strting the engine - both of which seem normal.

[Delfin]

Could be wet stacking from under loading of the engine.

[Copacabana]

Originally Posted by Delfin

Could be wet stacking from under loading of the engine.

Thanks Delfin. I had to look up "wet stacking" and I think it could be the case. As the problem developed, I just used the engine at lower RPMs to avoid smoke. I suspect I've been running the engine far too much below the optimal load.

Hopefully the new elbow and cleaning the manifold will allow me to go back to motoring at 2,400 - 2,600 RPM, thus preventing future deposits in the exhaust system.

[Delfin]

Originally Posted by Copacabana

Thanks Delfin. I had to look up "wet stacking" and I think it could be the case. As the problem developed, I just used the engine at lower RPMs to avoid smoke. I suspect I've been running the engine far too much below the optimal load.

Hopefully the new elbow and cleaning the manifold will allow me to go back to motoring at 2,400 - 2,600 RPM, thus preventing future deposits in the exhaust system.

If you crank it up to 80% power for 15-30 minutes a day, that should suffice.

[Copacabana]

I'll do that Delfin.

The big test will be if the engine gets up to high RPM under load after I put it back together and test it next week.

[stormalong]

Check your injectors. With the engine running at a fast idle briefly loosen each injector's high pressure pipe. You should have a noticeable drop off in speed and increase in vibration. If that does not happen the injector is bad.

How many hours on the injectors? Are you due for a change anyway?

[Copacabana]

Good question. When I bought the boat the engine had 2,200 hours. I don't know if the injectors have ever been serviced.

After how many hours should I service the injectors?

[stormalong]

Just my opinion - you are past due. On my engine I think the recommendation is every 1000 hours. I changed mine at 2000 hours and need to do them again now at 4000 hours. That is a Beta 50.

Check with the Yanmar.

[Copacabana]

Originally Posted by stormalong

Just my opinion - you are past due. On my engine I think the recommendation is every 1000 hours. I changed mine at 2000 hours and need to do them again now at 4000 hours. That is a Beta 50.

Check with the Yanmar.

Thanks Stormalong, I'll probably pull the injectors to have them serviced. I'm not sure if they've been serviced before and, unfortunately, the previous owner died last year, so I can't get this information.

[Compass790]

Could be compression issue as well as injectors. I would do a compression test as well when you have injectors out. Might be time for a valve grind. Have you ever done the tappet clearances? I would check those even before pulling the injectors.
If your compression is a bit too low you get incomplete fuel burn & less power. Yr model engine did have some piston issues. See sailorchicks thread

[gonesail]

2600 hours on the same mixing elbow would screw up any 3GM.

[Cheechako]

If it still doesn't come up to proper rpm after you start it with the clean manifold/elbow, you may have the 3GM30 broken piston curse...