Yanmar 2GM20F strong exhaust odor

[matts997]

I’m getting a strong exhaust odor in both the cockpit and cabin while underway. And when motoring for > 2-3 hrs, a fine, black residue can be found on certain white surfaces in the cabin (e.g., on white plastic cups in an aft cupboard). I had a mechanic do an inspection of the exhaust system…he reported everything was “OK”, except for the exhaust hose from the muffler to the thru hull, which he replaced—but this has not helped. There seems to be more than the usual black residue on the swim platform above the exhaust outlet, but I’m not sure what’s normal.

Not sure what next step to take. The mixer elbow has not been replaced since I’ve owned the boat (3.5 yrs) and the muffler could be as old as the boat (1996)—but not sure if these would cause the symptoms I’ve described. Engine has ~ 800 hrs and otherwise starts and runs extremely well.

Any suggestions would be greatly appreciated.

 

[jcela]

I’m getting a strong exhaust odor in both the cockpit and cabin while underway. And when motoring for > 2-3 hrs, a fine, black residue can be found on certain white surfaces in the cabin (e.g., on white plastic cups in an aft cupboard). I had a mechanic do an inspection of the exhaust system…he reported everything was “OK”, except for the exhaust hose from the muffler to the thru hull, which he replaced—but this has not helped. There seems to be more than the usual black residue on the swim platform above the exhaust outlet, but I’m not sure what’s normal.

Not sure what next step to take. The mixer elbow has not been replaced since I’ve owned the boat (3.5 yrs) and the muffler could be as old as the boat (1996)—but not sure if these would cause the symptoms I’ve described. Engine has ~ 800 hrs and otherwise starts and runs extremely well.

Any suggestions would be greatly appreciated.

Matts997
I have the same engine on my 29.5 and never had any black residue anywhere. It could be that the fuel mixture need to be adjusted, your mixture is too rich and your engine is not burning the diesel fuel completely and the black exhaust could be the indication of that. The adjustment screw is covered by a small hex cap that protects the adjustment screw. This is on top of the fuel pump and in my engine the cap is attached to the pump body with a fine steel wire so when you unscrew it off to discover the adjusting screw the cap wont fall off. Hope this helps.

 

[Dave Pawloski]

I had a similar problem about 10 years ago on my 1985 H-31.
Have you checked the exhaust manifold ??

 

[pateco]

I had that issue on my 2GM one of the Exhaust manifold bolts was snapped.

 

[kjretlaw]

I'd revisit the exhaust manifold and mixing elbow. it just takes the smallest leak.

 

[Panera]

My 2GM20 was pushing black smoke when I upped the RPM found that the bleeder valves on the starboard side of the engine were not closed tight allowing air to enter. Check to be sure they are tightly closed.

 

[matts997]

Thanks everyone, these are all good possibilities. My engine repair skills are almost nonexistent, so I'll be giving this list to my mechanic.

 

[Ken Cross]

You will be better off to pick up those skills. You have no better advocate than yourself.

Ken

 

[markwbird]

You have an exhaust leak. Usually the first sign is noise. Is the engine louder than it used to be? Often an exhaust leak will be rhythmic. Maybe sound like a knocking.

 

[matts997]

Agree Ken, I'd be better off picking up the skills--and necessity has forced me to start. Given the scarcity of diesel mechanics in my area, I can't get one out for > a month, so I started going through the list of suggestions in this thread and I think I've narrowed it down to the mixing elbow (MA: engine isn't louder or making any unusual noises). There are a lot of soot-like particles below and on the side of the engine that houses the mixing elbow, which itself has a lot of the same material on the outside of the elbow, especially where it connects to the exhaust hose, though the hose is tightly attached. I suspect the mixing elbow hasn't been replaced or cleaned in the last 10 yrs, if ever.
Not sure whether I can pull off removal and possible replacement myself....was a bit discouraged by this article, written by someone with far more mechanical skill & experience than I: https://www.sailmagazine.com/diy/maintaining-your-diesel-exhaust

 

[mark porter]

I am not a mechanic. I replaced my mix elbow and exhaust manifold gasket myself. It is straightforward when you look at it. The hardest part for me was getting the hose loose as it was baked in. I loosened the hose top as much as I could with a screwdriver, then soaked it with wd40 overnight. Came right off next day. After that it's all bolts to deal with. Quite simple, yes?

 

[Ken Cross]

Just one helpful hint here. The threaded part between the elbow and the manifold (between the two cast iron pieces) has one right hand and one left hand thread. This allows the parts to separate without unbolting it from the engine.

Not knowing that, I broke a manifold trying to separate the pieces when ours was clogged.
Ken

 

[Claude L.-Auger]

There are 4 only 12mm bolts holding the L-shaped piece to the exhaust manifold. 2 short and 2 long ones. The easiest way to remove the ex-elbow is to disconnect the hose at the horizontal muffler, then remove the 4 bolts and pull everything off. The hose from the elbow to the muffler is shorter than 3' and since the muffler is plastic the hose will not be baked on there. When you have everything out, it will become easier to take the hose off from the elbow. Do not forget to remove water inlet hose and bring it up higher than water line level. Better yet, also turn off your engine water intake through-hull to avoid any incident. You will need to scrape the manifold to clean bits and pieces of gasket then replace the gasket when re-installing the attachment. I found it easier to re-assemble the attachment and the elbow before re-installing the new unit to the manifold. The nipple in between elbow and manifold attachment is left hand / right hand thread. Chances are you need to take it to a shop to have it taken apart unless you can heat it almost red hot. Best price for a stainless steel elbow and nipple is a company out your way. Forgot their name but you can check E-bay. I've ordered from them and they also were able to supply the gasket. The whole thing was way cheaper than OEM. I've had it for 3 years now and everything is perfect. Good luck.

 

[kloudie1]

These guys are in Vancouver, Wa..
https://www.ebay.com/itm/GM-Stainle...c:USPSPriorityFlatRateBox!70816!US!-1&vxp=mtr

 

[matts997]

This is really helpful, thanks. Appreciate the link to the part. Decided to take this on late next month, when it won't interfere with fall sailing--just in case something goes terribly wrong.

 

[ManicFarmer]

I am a few years late to this thread but I am having this exact same issue. Purchased my 1990 Hunter 28 a few weeks ago. I am not seeing any residue in my cabin but I do feel it is an exhaust leak somewhere. It makes the cabin smell unbearable. Going to get the motor cleaned up and examine the manifold as well as the mixing elbow to see if I can find any issues. I do hear a knocking noise when the motor is running as @markwbird described.

 

[Justin_NSA]

You might even be able to detect the leak by running your hands wherever there's a possibility of one. You should feel pulsating air when you find it

 

[ManicFarmer]

You might even be able to detect the leak by running your hands wherever there's a possibility of one. You should feel pulsating air when you find it

Given how much odor it is putting out that is a good idea. I'll give that a whirl too! I'll post my findings and/or solution.

 

[ManicFarmer]

Came down here to take a look at the boat and I think I was off. I initially thought the smell was raw diesel but when I ran her for the first time last weekend I smelled it so assumed it must be exhaust. While the engine compartment stinks of a mixture of dust, fuel and 30 years of never being cleaned, I did find the source of the diesel. I do have a question but not sure if I should post here as it wasn't the issue.

I cross referenced the area that has some fuel on the line with the manual and it appears the problem area is the Fuel Feed Pump. The line that feeds it has a gasket on either side and I see some fluid on the line by the gasket. It has dribbled down a bit as well but seems to be a minor amount. None the less, that is definitely the odor. Should I just order the gaskets, clean up and replace? I wasn't sure if this would require a bleed or something. Let me know if I should move this to a new thread?

 

[bobmorning]

Find a Yanmar Owner's Maintenance school and take it. I went to a 3 day course at Mack Boring in New Jersey when we bought our 84 H31 11 years ago. Best money spent. Each student has the exact model of the engine for your boat and you are expected to do all the regular plus some replacement/repair maintenance. You don't get your completion certificate until you put the beast back together and get it to start and run.

You do fuel pump replacement, fuel filter replacement, water pump replacement, valve adjustment, alternator remove/replace, starter remove/replace, sea water pump periodic maintenance, heat exchanger cleanout, etc.

The guy teaching our class was older gentlemen whose experience and wisdom was worth the class price on it's own.

Bob