Our generator turned itself on last night—with no help from us!

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.


Senior Member
Mar 12, 2016
Vessel Name
Suu Kyi
Vessel Make
Custom 40' catamaran
Our genset is a Kubota–Onan 6.5Kva set. Last night, while we were asleep, it started up by itself. The seacock was closed...

We had run the set for an hour the day before, while on anchor. The front rocker switch was set to Auto, so we can start it from the helm position. We were back on the dock, on shore power at the time.

We woke up, and ran to the hatch where the genset lives, and turned on the seacock; water rushed out the exhaust. So, we will be inspecting the impeller, as a matter of course, and we have a spare on board.

I do not know how the helm switch to Start/Stop is wired, but with the set on Auto (meaning remote start; the other positions of the switch are Run and Off)—is it possible that our shore power failed momentarily, and that started the generator? This has never happened in the three years we have owned the vessel. And if auto-starting is a feature of this setup, we will be sure to leave the rocker switch on Off in future.
Last edited:
Very interesting. My auto start for the generator is hooked up to my xantrex inverter and it is programed to start when the battery drops to the preset voltage. Might you have a generator setting on your inverter?
We don't have an inverter (yet) but I imagine the 240V distribution board is wired in a similar way to your inverter, in that if a load is experienced on the board, the generator starts. I am assuming that, because of the recent floods here, shore power is shutting off from time to time, and that's what made the generator start.
Lucky you were onboard! Off position is the only option while plugged into the dock. I've never heard of that happening, but that's what makes electricity so scary-there's always an incident you hear like this.
In 10 years of our last boat equipped with the same generator, it never started without human input. Early on some batteries were in urgent need of replacement,so if it could, it should have. I`d investigate if the auto setting means auto start. We started it at the helm, not the genset. Have you got a manual for the generator? I`m sure I found one online once. I`d look for a fault.
Last edited:
I may need more info to answer this. Genset in auto will run if conditions meet. I’m guessing a 2 wire start system. Something got corroded and made genset start. Check wiring to upper helm or that switch at the upper helm.

Edit. Sometimes all a wire needs to start a genset in auto setting is a ground to close the loop
Thanks BruceK; yes, we do have a manual for the genset, but WRT that very point (what are the possible meanings of "Auto"?) the manual is not clear (meaning the manual does not talk about how the genset might be wired into the boat's 240V circuits). I'll report back. We do have the genset turned to the "Off" position and that's how it will be from now on, if on shore power. It was quite a shock.
Last edited:
Easy enough to try. Set it back to Auto, then turn off the shore power breaker and see what happens.

That said, it won't (or shouldn't) auto start unless someone has wired it up to do so.
@TowLou: nothing corroded at the lower helm position, where the genset Start/Stop switch lives.
@twistedtree: I will try that, but my guess is that turning of shore power on the board will simply disconnect that source, and the genset will not start.

This is just an idea at the moment, but I think that the wiring is set up to start the genset if shore power is switched as the source, shore power fails, and there are loads on the board (like hot water). The 240V panel has one of those switches (don't know the technical name) that has a bar that allows only ship power or shore power to be selected at the one time.
That sounds like the test to do, @SteveK. I will do this tomorrow (pissing down outside at the moment) and report back.
The plot thickens. Genset set to Auto, seacock on. 240V board set to shore power, with a number of loads (heater, hot water, lights). Disconnected lead from shore, nothing happened.

To be on the safe side, will keep genset seacock OFF; and genset to OFF on rocker switch when on shore power. Now, I have no idea why it switched itself on last night, but I will ask an electrician friend to have a look. Thanks to everyone who has commented.
A correction to the first post: the genset is a Kohler, not an Onan (that's on a neighbour's boat I was working on recently). Kohler; sorry about that.
Our insurance company told me that if our boat is left on a mooring, or on a dock, and sinks, and investigations show seacocks are open, then cover is void. And even though thru-hulls and seacocks are new a month ago, that's advice I have taken to heart. It might be silly (the Marine Rescue vessel I drive sometimes never shuts seacocks off) but it's a habit.
Why close the seacock if you’re on the boat?
I was wondering the same. It's odd for insurance to stipulate closing seacocks, I've never seen a policy that does. Personally, I wouldn't unless the boat is going to be unattended for a while. I figure if I can't trust the hoses, etc. then I need to fix them.

In general, any time I do close a seacock for something, I make sure to disable that device to prevent accidental use (and cause me to notice the seacock if I don't remember why it's not working). So for the engines, I trip the ignition breakers so the key switches won't work. For the generator, I turn the battery switch off so the start switch won't do anything.
Our insurance company told me that if our boat is left on a mooring, or on a dock, and sinks, and investigations show seacocks are open, then cover is void. And even though thru-hulls and seacocks are new a month ago, that's advice I have taken to heart. It might be silly (the Marine Rescue vessel I drive sometimes never shuts seacocks off) but it's a habit.
But you were on the boat. Sure close sea cocks when you’re off the vessel and for further insurance close the engine fuel supply line when off the vessel.
Could even be a bad relay in the auto circuit. What’s the model I’ll look see if I can look up the schematics.
It seems really important to figure out whether or not there is some sort of intentional autostart wired up for this boat. The answer leads to very different areas of investigation.

If there IS some sort of autostart wired up, then it has either triggered incorrectly, or triggered correctly and you just didn't expect it. But all your focus will be in the triggering criteria and circuitry external to the Kohler.

If there IS NOT some sort of autostart wired up, then you have a fault in the Kohler controls and need to dive into that.

I think I'd try to find out how you externally trigger this Kohler for autostart, and see if there is anything hooked up. There is probably a wire to signals it. Then proceed to chase down the external autostart triggering mechanism, or the internal Kohler controls, based on whether there is any external trigger source hooked up.
@TowLou: 6.527EFOZD

Re. leaving seacocks on or off when on the boat—perhaps this should be a new thread. Turning them off a) when I shut the mains down, and b) after shutting the genset down is second nature now—and seacocks and thu-hulls are all new three months ago. I do trust them.

@rslifkin: the policy that covers this vessel does not stipulate this; the close or leave open seacocks discussion came up in conversation with the broker. I had always closed the seacocks as part pf a close down sequence once tied up, and this habit might be like checking engine oil before starting—part of a setting off checklist. This practise also keeps the seacocks moving well.

If it is standard practise to leave seacocks open when on board, I will think about this.

@twistedtree: In nearly three years of ownership of this boat, the event that started this thread was the first. I have the genset centre rocker switch set Off now, so it can't self-start. I will ask a marine electrician friend to look at it when we are next at the marina.
Ok I have seen these controllers on the hard.

Do you have anything besides the remote switch like a transfer switch on the boat?

If you have no auto transfer switch onboard it’s between the genset and remote switch is your issue. While it’s in auto it’s gonna sit there like a dog looking at you holding a leash waiting for a walk. So either the remote switch is starting to fail or the wiring between the switch and genset is closing the loop to start. The RIB reacts and there is the start relay there. I wanna lean more on the remote switch or wiring from remote switch. Check wiring to the Relay Interface Board as well. If it is wiring all it needs is to be grounded to start on a 2 wire.

For reference.

Just saw you were in Australia makes sense bing a 50hz unit to. I want to go back there one day had a great time sand still talk to mates in Toowoomba
Hold up I just read before it is also has another connection to start your genset when shore power is faulty. Did you check if shore power was good? Maybe an imbalanced leg? That could be it. Don’t keep the genset in auto while on shore power. Got to also verify the shore power was faulty. That could have been it to.
I close the seacocks when I change the impellers and clean the strainers, but that's it.

Every time I leave the boat...ya gotta be kidding.
A bad relay or short in the starter can cause an unintended start in a diesel . Some years a fellow TF member had an unintended start that fried the starter and caused significant ER room fire damage.

Until this issue is sorted out it may be worthwhile to keep the genset fuel valve closed.
I appreciate everyone's suggestions. So, until further notice, genset rocker to Off, and fuel valve closed. I will be able to have this checked out at the Shellharbour marina in a couple of weeks.

@TowLou: we did pull the shore power lead while on shore power; and the genset did not start.

To everyone else: we do not close the seacocks when we leave the boat; we close them when we shut any of the engines down. Thanks for all the suggestions!
As I’m having my coffee by the river thinking and rereading this….. I’m thinking everything is working as designed. You had a power event that triggered the genset to start. If all the wiring checks out, the remote switch checks out by ohming it out and cycling it unplugged of course but when you do that stuff you should disable charger to genset and disconnect the battery so you do not short anything out. For a failed relay you need a failure of K2 (run relay) and K3 (starter relay) to start the run sequence.

I’d only switch it to auto with the seacocks open. The controller can call to start at anytime. Maybe the inverter was not calling for the genset to start right when you pulled the plug how low did DC volts go to before you restored AC power. As Mac2 says with his xantrax charger once the batteries drop it will call to start. Keep it unplugged for a while watch battery voltage see what happens it will not be right away. It’s not like a ATS where it will call to start for power right away unless there are settings in your inverter that can be modified to call to start once conditions are met to start. It may call to start once your DC voltage hits below a certain value by the inverter. I do not know how it is set up for you.

How about shore and genset switch does that change sources on its own or do you have to manually switch your AC power source from genset to shore? You will need to see what else is wired to your auto circuit.
Top Bottom