Yanmar 2GM20F Failure - reality check needed

Fredct

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Sep 21, 2020
86
Oday 28 Westbrook
1994 vintage Yanmar 2GM20F. Well maintained by previous owner. Yard has been doing annual oil change and winterizing. Worked fine for 4 years without a single problem.

In last 10 days, we did a NE cruise with about 20 hours of motoring over several days at 2000 rpm.

Here is full description in case timeline is important. Fuel tank is metal and 17 gal.

End of season 2020 - filled with diesel with stabilizer, oil change, winterizing
Start of season - no problem with starting
April-May - multiple day sails with about 20 hours of motoring total, no problem.

Trip
Day 0 = bled the fuel/water separator, refilled with new fuel, could not start the engine until I hit the solenoid with a hammer! Replacement starter on order. Started multiple times, no issue.
Day 1 = 8 hours of motoring, 2k rpm - no issue.
Day 2 = 2 hours of motoring - no issue
Day 5 = 6 hours of motoring - no issue
Day 6 = added 3 gallons of diesel, vintage June 2021
Day 8 = 2 hours of motoring, no issue
Day 10 = 6 hours of motoring, 2k rpm. After 6 hours, engine started to oscillate slightly in speed, as if the throttle was being pulled back and forth. Like a sine wave almost. Pattern would come and go. Wind picked up so we put up the sails, keeping the engine at idle. Out of nowhere, the pattern intensified and the engine stopped, with no response when moving the throttle, as if the fuel stopped flowing. We let the engine cool till we got close to our yard. With insurance card in hand, we cranked engine which started first time but RPM very erratic, we babied the throttle back and forth, seemingly with no effect at first until the engine revved UP as we throttled down. Brief puff of white smoke and then all was well, we motored into our berth and the rpm seemed very stable, albeit with a cooler engine. It was as if the engine burped...

So I am starting to do prepare a plan of attack. I am not sure about the root cause. My thoughts so far:

0- Replace the starter but unrelated to issue at hand
1- Water in fuel - I have Raccor separator so unlikely
2- Dirty fuel - I will change both primary and secondary filters
3- Air in fuel line - no obvious leaks but I will bleed when I change the 2 filters.

Are there any other possible root causes that would cause this intermittent failure? Injectors were taken apart and cleaned 6 years ago. I checked the throttle cable - no issue, same with shutoff cable, no issue.

As always, help appreciated.
 

Fredct

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Sep 21, 2020
86
Oday 28 Westbrook
Don, like a large piece of dirt obstructing the flow from the tank?

I thought about fuel pump and injectors but it seems that i would have bigger (more frequent) issues if those were faulty.
 
Jan 4, 2006
3,912
Hunter 310 West Vancouver, B.C.
The only problem I see in this description is running the engine at 2,000 RPM.
The recommended RPM should be 75% of maximum speed = 75% of 3,600 = 2,700RPM.

Having said that, Yanmar recommends much higher operating speeds as shown:
RPM info from GM operations manual.jpg

Good for the engine but not so good for fuel economy.

Running the engine for long periods at reduced load can result in a clogged mixing elbow:
Dirty Sectioned Mixing Elbow.jpg


This may be one place to look if your engine has a mixing elbow.
 
  • Helpful
Likes: ggrizzard

Fredct

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Sep 21, 2020
86
Oday 28 Westbrook
@ggrizzard I should have said that the tach broke on day 3 so speed is estimate. I cannot imagine running rpm higher, the noise level is already deafening. That said, will fix/replace tach and advise. Could be that our actual rpm was much higher than reported by faulty tach.

I have a mixing elbow that was replaced 4-5 years ago. Why would clogging be intermittent? I have not seen a gradual degradation of performance (measured in knots) in past 4-5 years. I say that but how one would know for sure. The difference between 5 knots and 4.8 knots is minimal and gauges cannot be trusted to be that accurate. I will check mixing elbow.

Thanks.
 

19thol

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May 2, 2014
111
Hunter 30 St.Petersburg, Fl
From my experience it sounds like a fuel delivery problem. One problem I had similar to your experience, had a pin hole in fuel line, sucking some air, not large enough for fuel to leak out. Replaced fuel line, all was well. Might also check filter housings to ensure no air being sucked in past an o ring or threads.
 

Fredct

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Sep 21, 2020
86
Oday 28 Westbrook
@19thol The leak was between tank and 1st filter or between filters? My access is cramped. Not sure that I can check everywhere. Will verify filter housing. Seemed OK but I was not the one putting it back on.
 
Apr 22, 2011
735
Hunter 27 Pecan Grove, Oriental, NC
As Don suggested, check the fuel pickup tube. Take it out of the tank and if there is a tiny screen inside the tube, remove it. A temporary fix is to disconnect the fuel intake hose at the racor filter while you are having the problem and blow into it. This should force the obstruction out of the tube.
 
Nov 6, 2006
9,226
Hunter 34 Mandeville Louisiana
Air leak or pickup tube clog, I agree. For the air leak, everything on the suction side of the fuel pump, including the banjo fitting at the pump. Shutoff valve stem packing at the tank, fuel lines
, all fittings.
 
Jan 30, 2012
1,093
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Consider a vacuum gauge - maybe $12.00 US which will work as long as you can see it during operation. You can pay more of course - for a tattle tail needle, oil filled unit that tells you the highest vacuum during any run which is handy if you can t see the gauge. Either way a gauge will eliminate nearly all guesswork in fuel supply cases.

Charles
 
Oct 29, 2005
2,187
Hunter Marine 326 303 Singapore
Sounds like foul take-up tube, foul in water-separator head assembly.
Had similar issue before.

Ken Y
 

Fredct

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Sep 21, 2020
86
Oday 28 Westbrook
Thanks to all. Making it much better. It's all in the category of serious but fixable. Will inspect, replaces filters, look for cracks - perhaps blow out the fuel line (with compressor?) if I can get to it.
 
Oct 29, 2005
2,187
Hunter Marine 326 303 Singapore
I
Thanks to all. Making it much better. It's all in the category of serious but fixable. Will inspect, replaces filters, look for cracks - perhaps blow out the fuel line (with compressor?) if I can get to it.
I clean out the racor head assembly and use dinghy foot pump to blow back chokage to tank. Yes dirt stays in tank which i then polish the fuel.

Ken Y
 

Attachments

Last edited:
Feb 26, 2004
21,959
Catalina 34 224 Maple Bay, BC, Canada
@Fredct , Ken's is a good candidate.

Here's a longer description, depends on what filter housing you have:

 
Mar 20, 2011
594
Hunter 31_83-87 New Orleans
The only obvious possibility is a clogged pick-up tube in the tank but it could be lots of things like bad injector, fuel pump, etc...
Fred. I had the same problem with the 2GM on my H31. Was offshore bobbing around in confused seas and mixing up the bottom of the tank even after recently having fuel polished. Had crud in the bottom and pickup tube was getting clogged causing the rpms to rev up and down. I was able to disconnect fuel line between tank and Racor and blow back thru it. That did the trick. Bled down the system and went back to running normal. Please keep us posted on how yours goes. good luck.
 
Oct 22, 2014
16,142
CAL 35 Cruiser moored EVERETT WA
Fred, sound like your on the right track. Fuel issues from debris on the bottom of your tank can cause the type of symptoms “rpm racing”. Also the removal of injectors or the associated piping can lead to an improper reinstall allowing air to leak in do to improper seal/old copper washer reused.

I had the dirt in the filter issue. Here is what a clogged filter looks like.
8578F89A-FFDC-4601-A7A6-B16092092455.jpeg

The vacuum gauge is a great tool to let you know when the problem is happening. If the filter is clogged the vacuum gauge rises showing fuel starvation. It there is a leak then you the gauge shows low vacuum. Air is leaking into the system and fuel cannot get to the engine.
 

Fredct

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Sep 21, 2020
86
Oday 28 Westbrook
Update for completeness.

Changed air filter (old one was oily, filthy).

Changed Raccor 10 micron filter. Engine started (took 2 attempts). Ran 5 minutes. RPM unknown as tach is broken.

Changed Yanmar 2 micron filter. I noticed that the filter housing was mostly empty of fuel when i took it off. I expected it to be full of diesel. Filled housing with new fuel, screwed it back on, bled for about 2 minutes, engine started first time. Sounded good.

As I was checking for fuel leaks at the filter housing, noticed that the alternator belt was oscillating. Alternator was at the end of its range. Brought it all the way in, changed belt with new Yanmar belt. Width of the new belt was double old one. Started engine. Sounded real good, with a good water flow in exhaust. My captain was not at yard to give second opinion on engine sound/flow/performance.

I still need to replace starter with Masco version. Next weekend.

Conclusion: Likely a combination of restricted air intake, air in fuel line and sluggish fuel flow (intake line or filters). Belt slippage may well have been a factor, especially at elevated temperature. Will do a full multi-hour test under load this week.
 

DougM

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Jul 24, 2005
2,183
Beneteau 323 Manistee, MI
You confused me with the belt slippage comment. What has that got to do with the fuel issue?
The two belts on the 2GM20F are the small one that drives the external water pump and the larger one that drives the alternator and engine water pump. As far as I know those really shouldn’t have anything to do with the fuel delivery.
At the age of your engine, I would seriously consider replacing the fuel lines completely. Microscopic pinholes could be allowing air into the fuel line, and/or the interior of the fuel lines could be disintegrating allowing particles to clog the filters or worse be small enough to get into the fuel injectors.