Onan diesel generator randomly shuts off

SeaNile

SeaNile

Well-Known Member
Aug 16, 2010
1,522
Chadds Ford, PA
Boat Info
2003 50 Sundancer
Engines
Cummins QSM11
Generator has been running fantastic, zero issues at all expect for today. Cruising along at 20knts and it shuts off. Wait till no wake zone and fire it up, starts but immediately shuts off after about 10 seconds. After cursing for about an hour we anchor for the afternoon. Generator fires right up and runs great for about 2hrs and then shuts off. Starts right back up for 10 seconds then shuts off.

Didn't have anytime at all to troubleshoot but the temp was fine, plenty of water discharge, new fuel pump about 3 weeks ago but the lighted gauge would bounce between yellow and 1 bar of green for battery voltage. Also when we initially anchored the GPS was showing low voltage with an alarm at 11.6 volts. Port engine seemed slightly low showing 12volts but then on the way home was at 13.5 as we were running.

Could a bad battery be causing the generator to shut off? It cranks quick and I don't think the battery is weak based on how it cranks the generator. Same for engines....no slow crank at all.

So I am wondering what could cause the generator to die like that, then start for 10 seconds then die but then run for 2hrs without issue and then die again.

I didn't get a chance to check the oil yet but that will be the first thing on my to do list on Friday afternoon.

Thanks.
 
Suggest you check the strainers as well.
 
SeaNile said:
Generator has been running fantastic, zero issues at all expect for today. Cruising along at 20knts and it shuts off. Wait till no wake zone and fire it up, starts but immediately shuts off after about 10 seconds. After cursing for about an hour we anchor for the afternoon. Generator fires right up and runs great for about 2hrs and then shuts off. Starts right back up for 10 seconds then shuts off.

Didn't have anytime at all to troubleshoot but the temp was fine, plenty of water discharge, new fuel pump about 3 weeks ago but the lighted gauge would bounce between yellow and 1 bar of green for battery voltage. Also when we initially anchored the GPS was showing low voltage with an alarm at 11.6 volts. Port engine seemed slightly low showing 12volts but then on the way home was at 13.5 as we were running.

Could a bad battery be causing the generator to shut off? It cranks quick and I don't think the battery is weak based on how it cranks the generator. Same for engines....no slow crank at all.

So I am wondering what could cause the generator to die like that, then start for 10 seconds then die but then run for 2hrs without issue and then die again.

I didn't get a chance to check the oil yet but that will be the first thing on my to do list on Friday afternoon.

Thanks.
Click to expand...
It should give you a flashing light code when it shuts off on the ON switch. Look at your manual it will show you what to look for to read the code. Or if you have the digital display for the geny it has a button to show you the shut down reason.
 
Model MDKBN?
There's several of us on this forum that are having issues with shutdowns when running on our starboard fuel tank. That is for the 500/52 DB's. Mine, it seemed, to be air in that long long fuel line to the starboard tank. Check your fuel configuration and first see if the Racor fuel level is down then switch to the other fuel tank and try again.
I have surmised in my case that the fuel siphons back to the fuel tank when the Racor lid is removed when the selection valve is on the starboard tank thus introducing air in the line. In fact it happens on both tanks but the port side fuel line is so short it purges right back no problem. I correct it by shutting the fuel selection valve off before servicing the Racor.
Anyhow, is the fuel level down in the Racor when it shuts off?
There is a raw water flow switch that can get problematic, it is in the raw water hose inside of the sound enclosure cover where the oil dipstick is. Unscrew it and flush it out. It is also subject to galvanic corrosion as it is not bonded so check for function also.
The electrical connections on the fuel solenoid and sensors are the spade type so check them for loose fits.
When it shuts down, the switch lamp should be flashing - that is a code for the fault. The faults are described in the Service Manual as @ocgrant states above.
 
Agree about fault codes.....However, I know you bought this boat recently. If you don't know the history of your batteries (all of them) I would suggest replacing them. From your description it sounds like your generator battery isn't holding charges anymore. And yes, this will affect your generator function as it requires battery to not only start the generator but to stay running.
 
Being erratic like that with no other ill signs on the gauges (particularly temperature) sounds like a fuel issue to me. Change the filters and see what happens.
I'm not sure how your battery is configured, but if it runs for two hours and shuts down, it is hard to imagine it is that, given you are likely charging that battery and it wouldn't be getting into a low voltage situation.
 
I have been chasing this for the last year. Right before shut downs I had low voltages. Both the battery and alternator tested fine.

One shop I talked to insisted that this was a fuel issue. My issue went from random to running less than 15 minutes constantly. A few weeks ago we ran it on an external tank for three hours. After that they blew out the lines but only on the starboard tank. It's run for 60 hours since then. I switched once to port tank, it ran for two hours.

I suggest first looking at the racor as @ttmott describes. If it's low you likely have a leak allowing air. If not you may have a blockage. My racor was never low. Changing filters never resolved my issue.
 
SeaNile said:
Generator has been running fantastic, zero issues at all expect for today. Cruising along at 20knts and it shuts off. Wait till no wake zone and fire it up, starts but immediately shuts off after about 10 seconds. After cursing for about an hour we anchor for the afternoon. Generator fires right up and runs great for about 2hrs and then shuts off. Starts right back up for 10 seconds then shuts off...
Click to expand...

These symptoms sound to me like the fuel starvation issue. As Scott indicated, isolating to a single source of fuel supply will lead you closer to finding the cause. Keep in mind that your boat is at the age when fuel houses are starting to go (probably internally). IMO, your observation of genny shutting down while on plane vs. idling or being anchored, is just a coincident.

As others mentioned, step #1 is understanding the error codes. If you don't have a digital display showing the full code, the easiest way to get it is at the start/stop switch (the light on the switch). When genny shuts down, it blinks amber color. Note that there are two sets of codes.

First set - Count the number of blinks, then ...
Second set - press and release the shutdown (lower part of the switch), it will give another number of blinks.

If I'm right, you'll most likely see the most annoying code 36 (3 blinks and 6 blinks).

So, let's get some input data/details so you can get more accurate recommendations.
 
I don't own your model generator, but I had the same symptoms on a Westerbeke, random shut downs. Frustrating as hell.

I at first thought fuel issue or air in fuel, then I looked at the safety switches and I found a bad exhaust overheat switch. It looked fine from the outside, but the contact had cracked/separated internally just enough to shut it down.

Your just going to have to methodically eliminate possibilities until you find the culprit.
 
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I'll be heading to the boat later today and will camp out in the bilge staring at the generator to see if any codes come up when it shuts down. My luck is it'll run fine for 6hrs and I'll spend my entire day in the bilge staring at a white noisy box.
 
SeaNile said:
I'll be heading to the boat later today and will camp out in the bilge staring at the generator to see if any codes come up when it shuts down. My luck is it'll run fine for 6hrs and I'll spend my entire day in the bilge staring at a white noisy box.
Click to expand...
Set up a video camera.
 
The codes flash repeatedly for at least 15-20 minutes so no need to camp out. Just don't go far for more than 15 minutes.
 
Starts right up and running great for 10 min so far under load.

Battery looks low. I’ll keep an eye on the voltage.
 

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Battery is slowly coming up. Oil level is good, water flow out of hull is good.

Shut off 3x now.

3 flashes and the reference says “service needed.”

That’s no help!

Just found out that I need to get to the secondary codes. Once I figure out how to do that and get the secondary code that should give me a lot more information.
 
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SeaNile said:
Battery is slowly coming up. Oil level is good, water flow out of hull is good.

Shut off 3x now.

3 flashes and the reference says “service needed.”

That’s no help!

Just found out that I need to get to the secondary codes. Once I figure out how to do that and get the secondary code that should give me a lot more information.
Click to expand...
Do you have your Service Manual? They are available online. Mine covers 7 different models. What is your model?

So the first code blinks, then a pause, and the second code blinks...
 
3 blinks, then pause then 3 again. Manual says to goto the secondary code and count.

I’m thinking I need to press the button to get to the secondary codes.
 
Code 58
Exhaust gas temp too high

panel confirms over heating.

Impeller? Barnacle buster?

Took about 90 min of running for it to shut off/over heat.
 
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