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Old 27-12-2014, 18:06   #1
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Yanmar diesel motor randomly started on its own

Hi, just had a spooky thing happen this morning. After having a swim I was drying off and my port motor started randomly on its own, no one was near the helm, no keys in the igridiron, ran down and checked the isolator switches were turned off. I don't believe there to be any other source of power but how the hell did it start. We had just come in from a rough journey, but it's very straneg. Never done that before.
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Old 27-12-2014, 18:52   #2
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Re: Yanmar diesel motor randomly started on its own

Yes, it seems to be quite a common problem. There have been a few other threads about the same thing. I will see if I can find them.

I didn't come across anything specific to Yanmar but there are a number of threads for Perkins that might be worth reading through. It is a short somewhere in your wiring that is causing the start solenoid to energize.
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Old 27-12-2014, 18:58   #3
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Re: Yanmar diesel motor randomly started on its own

It does happen sometimes. Older universal engines had a wiring plug which could degrade over time and cause intermittent shorts. A short could develop in your starter solenoid relay switch. That could cause this problem.
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Old 27-12-2014, 20:09   #4
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Re: Yanmar diesel motor randomly started on its own

Most likely caused by a short in your wiring somewhere. Consequential damage could likely be a fried starter motor if the short made it stay engaged whilst the engine was running. Check for that as well as finding the initial fault.
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Old 27-12-2014, 20:50   #5
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Re: Yanmar diesel motor randomly started on its own

This is the very reason there should be a switch between the start battery and the starter.
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Old 27-12-2014, 21:15   #6
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Yanmar diesel motor randomly started on its own

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Originally Posted by Terra Nova View Post
This is the very reason there should be a switch between the start battery and the starter.

There is, it's the start relay that scotty spoke of, I know you meant a mechanical disconnect, real easy to add one if you feel the need, I would add it to the small wire powering the realy, if you want to disconnect the big wire to the starter, that of course would be a big battery disconnect.

I guess maybe if you don't at least make sure it's always in neutral?

Biggest concern is a fire when you weren't even on board?
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Old 27-12-2014, 21:50   #7
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Re: Yanmar diesel motor randomly started on its own

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...I would add it to the small wire powering the realy...
This is insufficient. There must be a battery disconnect between the starter and the battery.
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Old 27-12-2014, 21:52   #8
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Re: Yanmar diesel motor randomly started on its own

The OP stated the isolator switch(s) were off and presumably the boat was not moving as he had just been swimming so how did the engine start???

Presumably the isolator switch does not isolate...
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Old 27-12-2014, 22:09   #9
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Re: Yanmar diesel motor randomly started on its own

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The OP stated the isolator switch(s) were off and presumably the boat was not moving as he had just been swimming so how did the engine start???

Presumably the isolator switch does not isolate...

I wondered about that too, if I turn my isolator off, just my bilge pumps and one or two other things are powered, why would you turn them off if your in the boat?
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Old 27-12-2014, 22:32   #10
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Re: Yanmar diesel motor randomly started on its own

So when you go swimming, you turn the battery isolator off, removing power from the refirdgerator, clock on the stereo, etc?
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Old 27-12-2014, 22:42   #11
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Re: Yanmar diesel motor randomly started on its own

If your stereo, clock and refrigerator are on your engine start battery switch, your boat is wired wrong.
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Old 28-12-2014, 02:03   #12
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Re: Yanmar diesel motor randomly started on its own

Most older boats are normally fitted with a 1,2 or both battery switch which means the engine is live no matter which setting your switch is on. (Except of course the OFF position )



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Old 28-12-2014, 09:27   #13
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Re: Yanmar diesel motor randomly started on its own

For those older boats it is a simple matter to install an ON-OFF battery switch in the starter cable.
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Old 28-12-2014, 09:39   #14
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Re: Yanmar diesel motor randomly started on its own

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Originally Posted by NoTies View Post
Most likely caused by a short in your wiring somewhere. Consequential damage could likely be a fried starter motor if the short made it stay engaged whilst the engine was running. Check for that as well as finding the initial fault.
I don't know in which year the 'safety switch' was added to yanmar diesels, but this switch breaks the connection to the starter motor when the engine starts. So, the starter motor should not be damaged.
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Old 28-12-2014, 11:37   #15
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Re: Yanmar diesel motor randomly started on its own

Had a 6-71 powered dive-boat with a huge bilge pump wired with #8. When it kicked in the induced current in the common harness would close the relay to the slave solenoid and start the engine.
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