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Old 08-09-2014, 09:44   #1
njb
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Yanmar 3GM30 losing power and dying after motoring continuously

Hello All,

A few weeks ago, I was out in the boat and ended up motoring continuously for a few hours (more than usual, my standard practice is to just use the motor getting in and out of the mooring field and anchoring occasionally). Shortly before getting back home, the engine started to lose power, and then died. It would restart, and then sputter and die again.

As I was overdue for a filter change, and hadn't put any fuel in the tank for over a year, I replaced both fuel filters, changed the oil, and then had the tank polished and the fuel cleaned.

Fast forward to this past week, I was out cruising and using the engine more consistently, probably put about 20-25 hrs on it over the course of the week (since the previous maintenance). After motoring continuously for a few hours yesterday, the engine again lost power, died, and then would restart but die again.

My mechanical knowledge is limited, but I found it suspect that the fuel level in the tank seemed to have been drawn down to roughly the same level during both episodes (approx 3/4-2/3 full). Given that filters and the fuel are all supposedly in working order, I am wondering if this is an air leak/vacuum issue associated with the tank??? Or the pickup in the tank?

Any thoughts or advice would be appreciated.

Thanks,
Nick

Allied Seawind 30
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Old 08-09-2014, 10:19   #2
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

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Originally Posted by njb View Post
Hello All,

A few weeks ago, I was out in the boat and ended up motoring continuously for a few hours (more than usual, my standard practice is to just use the motor getting in and out of the mooring field and anchoring occasionally). Shortly before getting back home, the engine started to lose power, and then died. It would restart, and then sputter and die again.

As I was overdue for a filter change, and hadn't put any fuel in the tank for over a year, I replaced both fuel filters, changed the oil, and then had the tank polished and the fuel cleaned.

Fast forward to this past week, I was out cruising and using the engine more consistently, probably put about 20-25 hrs on it over the course of the week (since the previous maintenance). After motoring continuously for a few hours yesterday, the engine again lost power, died, and then would restart but die again.

My mechanical knowledge is limited, but I found it suspect that the fuel level in the tank seemed to have been drawn down to roughly the same level during both episodes (approx 3/4-2/3 full). Given that filters and the fuel are all supposedly in working order, I am wondering if this is an air leak/vacuum issue associated with the tank??? Or the pickup in the tank?

Any thoughts or advice would be appreciated.

Thanks,
Nick

Allied Seawind 30
It's possible if you have an exhaust goosneck riser it has filled with soot. Yanmar recommends changing the riser based upon numbers of hours/years in service. Some sailors have accumulated over 1,000 hours before having to replace the riser, others suprisingly few. It's a major, nearly impossible task removing the soot sufficiently to reuse a riser, so replacement at a DIY cost of around $150 is probably the way to go. Carrying a spare is recommended since we'll never really know how long a riser will remain in service before requiring replacement.

I suspect longevity may be related to whether or not an engine is low emission and how it's used.
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Old 08-09-2014, 10:28   #3
njb
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

Hmmm, pretty sure I had the exhaust riser replaced in 2012 (it was clogged and rusty, exhuast was belching white smoke over 2000 rpm. Also had the injectors sent out and cleaned at that point). Engine has almost 1100 hours on it now and I can't imagine it's seen more than 100 hours since that work was done. I'd have to check my records.

If the exhaust riser were at fault, what would explain the normal operation between the episode I had a few weeks back and the one this past weekend?

Thanks!
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Old 08-09-2014, 13:07   #4
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

Before you spend any money, try running with the fuel cap loose, you may have a clogged vent, or of course pull the vent line loose from the tank and blow through it.
I discovered during my delivery that all three of my vents were clogged with dirt dobber nests, fuel, balck water and drinking water
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Old 08-09-2014, 18:15   #5
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

Could be a weak lift pump. Between the filter and the injection pump there should be a low pressure pump to supply that injection pump. If this happened when the fuel level went down lower than the inj pump, maybe the lift pump is not working.
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Old 08-09-2014, 18:36   #6
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

if the fuel tank vent is ok .. can you bleed the injectors using the lift pump? if not it is easy and cheap to replace. .. especially if it is the original 3GM part.
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Old 08-09-2014, 18:41   #7
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Hey you fast forwarded through an important part. Did changing the filters solve your problem momentarily and now the engine's doing the same thing? If that's the case you probably have a dirty fuel tank you can polish the fuel but when you get out bouncing around stuff will break off and stir up clogging the filter. Anyway it's easy enough to find out. Change the first filter and don't throw it away because it possibly not the problem but that would be my guess. And the best starting point
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Old 09-09-2014, 09:39   #8
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

I'm going to vote lift pump needs replacing. If the OP's boat is like mine about 1/2 the fuel tank is above the injector pump, so fuel will gravity feed to the IP, up to a point.
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Old 09-09-2014, 15:00   #9
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So when you changed your filters the first time and had the fuel polished I take it you topped it up? So this time do one or the other if just topping it up solves your problem you "know" its the lift pump. If just changing your filter solves the problem...
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Old 09-09-2014, 15:12   #10
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

if the 3gm lift pump is original equipment (which it probably is) then it may be 25 or 30 years old. it doesn't have to be leaking to be defective. yanmar says the fuel should come out of the lift pump in strong bursts if you are wanting to test it.
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Old 09-09-2014, 15:41   #11
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

Thanks all for the thoughts and sugestions. I need to get over to the boat to test out some of these theories....

The lift pump is original (as far as I know) but the engine was new in 2000-2001 and has about 1100 hours, seems premature for a failure? When you say the fuel should come out in strong bursts, is that from operating the manual lever, or with the engine running?

Is the lift pump replacement something I could easily do myself? I guess the interim fix (assuming that's the problem) is to just keep the fuel topped up!

Sparrowhawk: You're right I may have too many variables at play here. I will try to isolate. When the engine first died a few weeks back, It would restart but die immediately (within 30 secs). After replacing filters I was able to run the engine fine at idle for a 20-30 minutes, then ran over to the marina to have the fuel polished/tank cleaned (10 minutes of motoring). Then ran over to the fuel dock to top off the tank (another 10 minutes). This would seem to indicate that the fuel level (and thus the lift pump) are not the main culprit? Hard to say. As I mentioned, the engine ran strong for about 20-25 hours since that work was done. Then the loss of power and slow death recurred.
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Old 09-09-2014, 16:25   #12
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I have a friend that installed 2 filters with a valve so he can switch filters instantly because his tanks are so dirty. With this system he can even change filters without turning the engine off
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Old 09-09-2014, 16:36   #13
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

I like the vent idea or the lift pump. The symptom seemed to be after extended running.. so I'm liking the vent issue for this problem. Another test is when it stops running... open the tank fill and see if there is a vacuum.
Another possibility is gunk in the tank migrating to the pickup screen after extended running... but I think you said you had the tank polished..?
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Old 09-09-2014, 17:15   #14
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Re: Yanmar 3GM30 losing power and dying after motoring continuously

Check your exhaust system, specifically the lift system. This is a common problem with installation. I myself had to purchase a new engine because of this.


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Old 10-09-2014, 08:10   #15
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Just thought I'd point out that if you're turning the engine over for a while with it not starting you need to turn off the raw water supply seacock otherwise the exhaust may fill and flood your engine with seawater.
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