Calling all Engine Heads...

[mgoodale]

Ok, looking for an engine differential diagnosis.

1985 Yanmar 2GM20F

Motoring out into channel, kick it up to 2400 RPMs at my usual spot, throttle goes all way forward, RPMs decreasing instead, oops, swing boat around with lots of traffic, yell at wife and sister-in-law to break out dock lines (sister-in-law can't tie a cleat hitch), barely make dead stick landing at end of closest finger pier before engine dies. Make visual inspection, no water or diesel leakage, try and start engine again, starts, then dies about 5 seconds, no smoke, but notice what looks like a carbon or exhaust sheen slowly coming from raw water exhaust. Call BoatUS, use unlimited towing back to slip.

Tow boat guy, old salt, says it's definitely a fuel problem.

Wait 2 weeks, then go and change both fuel filters, notice beautiful diesel and no sludge in either primary or secondary. Use bleed screw on secondary with hand pump, get good flow and pump until no bubbles. Do not bleed anywhere else, for example, at the fuel injectors or high pressure line. But I have only bled at secondary filter with hand pump and have never had any issues with air in lines. Try and crank engine, it cranks, then immediately dies, again, with a little of that carbon sheen coming out the exhaust at the transom. I put my finger in it, definitely not oil, like exhaust carbon in water.

Other things, maybe related or not.

Mixing elbow extremely rusted on outside. When I bought boat 5 years ago, mechanic who did work on engine said that elbow worried him, he would change it given how rusted it was on outside. Also, I have very poor access to the back of my engine, but leaned in and noticed that hoses leading to mixing elbow are also deteriorating.

Fuel: I usually keep tank at 3/4 to full and use biocide. This year I let tank get to 1/2 and have had some bumpy rides, but again, no sludge in filters.

Black spray: I have noticed back in my engine housing, under and around the mixing elbow, a small amount of black spray on the bilge paint.

Fresh water hose: while doing an examination, I noticed that the fresh water line was resting on top of the engine block and gradually making a hole in the rubber. I don't have any fresh water or coolant leakage yet and not overheating or loss of coolant, but I will have to re-route or secure regardless.

So what do you all think?

 

[Don S/V ILLusion]

Sounds like a lot of deferred maintenance issues, any number of which could cause the problem. It's almost impossible to tell via internet but it wouldn't hurt to start with the exhaust elbow which might be a likely suspect.

 

[Steve Dion]

Pull the fuel pick up tube. The "had" a screen on them when new. You will ptobably know right away if that is the problem.

I would r/r the elbow too.

 

[kloudie1]

I think Steve has this one right on .. if the outside of the elbow is bad, the inside is probably terrible, but it would not make it kill, it would instead act as if overloaded , but still run.. Pull the pickup tube and remove the wire gauze in the open tip .. make sure the tank vent is open and has not been plugged by spiders or mud daubers.

 

[s sauer]

28.5 and Yanmar 2GM20F

If you haven't cleaned or replaced the water injection elbow, you are way over due. If you intend to do it yourself, we've addressed this in detail in the past on www.huntertwentyeightfive.com.
I've opened up the polyethylene fuel tank on our 1986 28.5 and there is no screen on the bottom of the fuel pick-up tube. Adding a 6" clean-out / access opening to the tank will allow you to clean it out completely. First verify this is not a built-in fuel tank as some 28.5's seem to have... and they ultimately fail.

 

[Benny17441]

The fuel system on the 2GM is a little tricky to bleed the air out of. I find the little lever on the lift pump to be kind of inadequate to do a proper job. I do it by having someone crancking the engine while I crack the bleed screws open. I do start at the secondary filter and if the engine does not start by the time all the air is out I move on down the line to the high pressure pump and injectors. While crancking the engine you may want to close the raw water intake valve and make sure you open it as soon as the engine fires. I would also place a towel to collect the fuel coming out of the bleed screws. Once the engine fires and it should once you get all the air out then you can move on to diagnose why it may be quitting. Like Kloudie indicates verify that the fuel tank vent is not obstructed. It seems like suction may have been lost in the fuel line and the engine quit once the fuel already in the line was used up. That could happen because of a blockage or fuel leak allowing air into the system. Sometimes a pin hole in the fuel system allows for air to seep in when the boat seats unused for a week or two.

 

[Claude L.-Auger]

Benny's idea of cranking the engine works extremely well...and fast. If you're hesitant about having the engine fire up with your hands trying to shut off the bleed screw, decompress the engine before cranking. It will not start but will turn very rapidly when you hit the starter button, thus bring fuel up quickly. Crank until you get clean fuel, shut the bleed screw, clean up whatever spillage you created and fire up. Don't forget to re-open the water valve !

 

[Benny17441]

Claude is right the use of the decompression levers will prevent the engine from firing and make the job cleaner. After many times of bleeding fuels systems while the boat was underway I shortened the process by combining bleeding and testing for the engine to start in one motion. Most of the time after bleeding the secondary filter the engine will sputter and fire while running roughly until it expells any remaining air by itself. If it don't start then you need to go down the line cracking the other bleed screw. Keep your hands away from the belts.

 

[robertsapp]

Shortly after buying our boat, my engine (3GM30F) started slowing down on its own. Then it shut down. I could restart it, but it would pretty quickly stop running. Then it refused to start at all. The whole time, I was noticing a black sooty discharge that I originally thought was oil, but eventually determined was soot in the water. Moral of the story was - I had a completely plugged exhaust elbow. Coked up with a rock solid chunk of baked carbon. Couldn't budge it with a hammer and chisel. I bought a new one and haven't had a problem since.

I'm pretty sure the problem came from the fact the PO would only run the engine at 1500 rpm, way below where it needs to be run. If you haven't taken your elbow off and looked at it, I'd start there. Sounds like it's due anyway. They don't last forever.

 

[JST123]

I just recently had the same issue with my 2GM20F. Claude and Benny are correct that bleeding this can be a challange. Bleed the Secondary, then the primary, thenn supply line from the primary to the fuel injector pump, then the injectors.Use the decompression levers until fuel flows. And in all cases close what you are bleeding while still pumping other wise air can reenter the system. I bet it will start!

 

[robertsapp]

It's often said that if you give a diesel an adequate supply of clean fuel, fresh air, and proper lubrication, it will run forever. What is often completely overlooked is the fourth essential component - low exhaust back pressure. An engine with a plugged exhaust will not start.

We have an individual who admits he hasn't touched his exhaust elbow in the five years he's owned his boat. No idea when the previous owner might have serviced it. Fuel starvation doesn't generate soot in the exhaust. A plugged elbow does. I'd start there, because you need to look at it, regardless. It's long overdue.

 

[ChessieSailor]

First of all, many thanks for all the input. The likely problems were either (1) fuel, or (2) the exhaust system. The problem was that these went down quite different paths, different levels of troubleshooting, time, expense, etc. I did a level 1 fuel troubleshoot first, that is, replaced both fuel filters, added fuel and new biocide, bled the engine, but no avail. I could have done more with the fuel issue, but decided to go directly to the much more significant mixing elbow. The access to that side of my engine on my boat is almost ridicously bad, almost like Hunter didn't want owners or mechanics to work or replace anything aft of the cylinders.

Anyway, Bayshore Marine in Annapolis sold me the mixing elbow, lower elbow, reverse threaded joint, and gasket for 370. The idea of trying to remove only the mixing elbow and clean it was out of the question. My friend Warren agreed to assist and we went to it in hot and muggy conditions below. I spent many hours lying on top of the engine block in very difficult circumstances, but in the end we managed to remove the entire exhaust column (difficulty level 4), install the new column (difficulty level 9+), and then the 3 hoses I have on my system, which are the 2'' exhaust hose, and the 2 5/8'' hoses that enter my cockpit locker and are joined with a vented loop. Attaching the new 2'' hose from the muffler to the elbow involves a tight run with a very stiff hose (difficulty level 6).

So after getting everything put back together and losing about 3 pounds in sweat, I had the simple task of connecting the 5/8'' hoses to the vented loop. In the process, the OEM plastic vent snapped off. Ugh! No firing up engine, had to go back to Bayshore the next day and pick up a Scot Vented loop, another 50 bucks.

So yesterday, everything reassembled, hose clamps hopefully secured, I hit start and whoom, the engine fired up beautifully. It had a sound like a purring that I hadn't heard before. I ran it at different RPMs and noticed that the excessive vibration at idle had almost disappeared. I think I have been slowly killing my little 2GM20F with deadly back pressure.

So for those who say that an engine won't just stop because of a clogged mixing elbow, it will, if the elbow is clogged enough. And this symptom mimics the symptom of bad or clogged fuel, except as one of you rightly said, you don't get soot in the exhaust just because of bad fuel. I only hope that the back pressure didn't cause any other issues that I will find out later.

So what did the mixing elbow look like when we pulled it? See photos. It's hard to see, but the inside of the elbow looked to be about 100% clogged. We couldn't see any opening at all. There were also large chunks of coke in the hoses, falling out all over the place, and I mean quarter and larger size hard chunks, almost like rock.

So that's the story. Let's hope the engine rewards me with a good rest of summer and fall. Oh, and I got two new fuel filters out of the process, which can't hurt.

 

[s sauer]

Salvage Exhaust elbow

You can take the whole assembly to a muffler shop and they will likely be able to separate the three parts. The cast elbow fron the back of the engine can easily be cleaned and refurbished to like-new condition. The left and right threaded stainless steel riser may not survive, but if intact can easily be cleaned. Lastly. the bronze water injection nipple can be removed and slavaged. The "U" shaped casting is the most difficult to clean and least likely to be salvageable. I have been able to clean it with a Dremmel tool anda power drill with various wire wheel and grinding attachments.

 

[Rich M]

Having had similar access issues a few years ago on my 28.5 I decided to make a small change. Basically removed the back panel of the engine compartment and cut it to create a locking door on 2 hinges close to the centerline of the boat. This gives me great access without standing on my head or laying on top of the engine. With a mirror and a light I have found this modification to be very useful.