Oily deposit in exhaust manifold and mixing elbow- cause?

[Copacabana]

Originally Posted by 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...

I hope not!

But would the engine start easily and run fine at lower RPMs (up to 2,200) with a broken piston ring? It seems that the engine is fine, except under higher loads (when it smokes).

I'm hoping the new elbow and clean manifold will solve this problem, but if it doesn't, I'll pull the injectors and probably the head too for a refurbishing.

The problem is that it's the height of summer and I want to go cruising...

[Cheechako]

Originally Posted by Copacabana

I hope not!

But would the engine start easily and run fine at lower RPMs (up to 2,200) with a broken piston ring? It seems that the engine is fine, except under higher loads (when it smokes).

I'm hoping the new elbow and clean manifold will solve this problem, but if it doesn't, I'll pull the injectors and probably the head too for a refurbishing.

The problem is that it's the height of summer and I want to go cruising...

I had two that went bad. (catamaran) One at about 500 hours and one at about 2200 hours or so IIRC. Both started, one readily , the other became a bit tempermental to start. Neither would reach the previous higher rpm though. But sounded smooth at 2000 rpm or so. It's the lowest piston ring groove that breaks, I think there are 4, so the engine still has some compression when broken.
But you may not have that issue at all....

[Sardean]

Originally Posted by gonesail

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

Thanks for this information, is a 3JH3E mixing elbow likely to screw up the motor, and what exactly breaks and what do we look for, i have 1900hrs and my elbow is S/S.

[S/V Alchemy]

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.

You also want to check your prop pitch to ensure it's not partially to blame for not getting up to full revs. This, in other words, may be a two-part solution in that the gunk accumulated because the engine was lugging a bit. Much depends on your usage profile. If I motor, I motor at 75% WOT for over one hour as SOP in order to keep the diesel happy and avoid deposits of this type. That said, I have to flatten my pitch a bit to get my RPMs into the ideal zone for the fuel map.

[Copacabana]

Originally Posted by S/V Alchemy

You also want to check your prop pitch to ensure it's not partially to blame for not getting up to full revs. This, in other words, may be a two-part solution in that the gunk accumulated because the engine was lugging a bit. Much depends on your usage profile. If I motor, I motor at 75% WOT for over one hour as SOP in order to keep the diesel happy and avoid deposits of this type. That said, I have to flatten my pitch a bit to get my RPMs into the ideal zone for the fuel map.

Thanks for the reply. Nothing has changed with the prop for 17 years, so I'm not sure it's the immediate problem. The PO used to motor at 2,600 RPM and the engine performed perfectly. I suppose the big test is next week when I test the new clean elbow and manifold.

[01kiwijohn]

If your oil consumption is still normal, at the engine hours you've got, assuming you've checked all they other items mentioned, I'd certainly get the injectors serviced. The cracking pressure should be about 2500 PSI and the spray pattern should be regular, with a clean shut off.
At 2000 hours, mine were down to 1960 to 2100 PSI. Once re-set, it ran noticeably better, started quicker at cold temps., spooled up quicker too. Cost about US $110, and I did the R&I. At close to 4,000 hours, I plan to do them again and have the pump performance checked as well. My annual oil sample showed a little fuel dilution, so it's time.
I have come across a couple of engines where they'd burned up a piston because of neglecting this service.

[mowerandy]

Mate recently had a protracted problem with his 2GM20 that sounds very similar to this. He had a broken exhaust elbow that we found early in the piece (where the water guide flange had rusted right off the inside of the elbow). Was starting just fine, then dying within a few seconds, with brown smoke. Plenty suggested that perhaps she couldn't breathe on the exhaust side, but the exhaust system was quite clear.
Eventually the problem was found to be that the exhaust channel in the cylinder head above the exhaust valves was virtually plugged solid with hard black deposits. This was around a corner and out of sight inside the head, so not easy to find. Poked clear and the problem was resolved.

I reckon the brown smoke might be quite diagnostic, though I could find no mention of that anywhere. I also wonder if the broken exhaust elbow was somehow responsible - the entry point of the water into the exhaust is right alongside the head in that model. With the internal guide flange gone, seawater could potentially splatter back into the exhaust ports of the head, especially at lower revs, so perhaps helped to cause the problem...