Onan diesel generator randomly shuts off

Doubtful it's the impeller, there is a sensor for water flow plus I think you mentioned good water flow.

Heat exchanger is a maybe but I would think you would get a coolant overheating first which is another sensor.

Any blockages in exhaust at all? Loss of exhaust gas flow would lead to higher EGT I would guess since it lingers longer.

This is why I like having the display since it at least shows temp and oil pressure along with voltages and frequency. It also gives you a code you don't have to count flashes at 2am!

Just realized you posted pictures of some gauges, that temp of 195 is way warm. Mine runs at 165-170 depending on outside temps.

I would barnacle buster the heat exchanger.
 
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.
I had mine shut down after running 3 hrs. I noticed it was getting louder compared the the 58 that I was rafted with, steam was coming out of the exhaust and the temp was right at the redline. Hi EGT shutdown. HE was supposedly serviced 4 months earlier. Took the end cap off, had to use a 12" BBQ wooden skewer to rod out the HE - completely clogged. I then loaded it with BB through the strainer with about 5 start/shutdown cycles, and let it sit for 4 hrs, You should have seen the white foam that came out when I started it. No problems since...
 
The exhaust temperature switch is behind and on the starter motor side of the genset. It is right where the exhaust hose connects. S5 is that switch. One side goes to the ECM ground and the other uniquely to the ECM. There is no sensor loop. It is friction spade terminals on that switch so if you have ample water flow and the genset isn't overheating then check those friction connections on the switch. My generator sprays the raw water a good two to three feet away from the boat.
 
Started up at 1130pm and a ton of mud, dirt shot out immediately followed by white particulate then a lot of white foam. Ran great but I thought I noticed excessive smoke. Couldn’t tell if it was from the high humidity level or if it was from shining a spot light directly into the exhaust so I shut it down.

Fired right up this morning and zero smoke at all, temps seem to be about 10 degrees cooler and so far so good.

Any idea what the oil pressure should be while running? I can’t find it anywhere in the manual. The dummy gauge goes from 0-20-23-65-100. I’d say it’s fluctuating between 40-65 but who knows on this gauge. It’s to the right of middle visually on the gauge but it seems as if all is well.

I have to say the barnacle buster is addicting. I can’t wait to flush out the mains. Only thing is west marine has the pre mixed bottle for $70/gal. I’ll need 20 gallons for each engine. I can’t imagine it’ll really cost that much.
 
Started up at 1130pm and a ton of mud, dirt shot out immediately followed by white particulate then a lot of white foam. Ran great but I thought I noticed excessive smoke. Couldn’t tell if it was from the high humidity level or if it was from shining a spot light directly into the exhaust so I shut it down.

Fired right up this morning and zero smoke at all, temps seem to be about 10 degrees cooler and so far so good.

Any idea what the oil pressure should be while running? I can’t find it anywhere in the manual. The dummy gauge goes from 0-20-23-65-100. I’d say it’s fluctuating between 40-65 but who knows on this gauge. It’s to the right of middle visually on the gauge but it seems as if all is well.

I have to say the barnacle buster is addicting. I can’t wait to flush out the mains. Only thing is west marine has the pre mixed bottle for $70/gal. I’ll need 20 gallons for each engine. I can’t imagine it’ll really cost that much.
Nah you don't need 20 gallons. It'll take about 5 or 6 gallons to fill and circulate then let it drain back to the bucket and do the other engine. You can reuse this stuff over and over. Just make sure you generously flush with dock water to get as much mud and growth out before the BB. It is the circulating of the BB that really gets the calcium out of the raw water system.
 
Started up at 1130pm and a ton of mud, dirt shot out immediately followed by white particulate then a lot of white foam. Ran great but I thought I noticed excessive smoke. Couldn’t tell if it was from the high humidity level or if it was from shining a spot light directly into the exhaust so I shut it down.

Fired right up this morning and zero smoke at all, temps seem to be about 10 degrees cooler and so far so good.

Any idea what the oil pressure should be while running? I can’t find it anywhere in the manual. The dummy gauge goes from 0-20-23-65-100. I’d say it’s fluctuating between 40-65 but who knows on this gauge. It’s to the right of middle visually on the gauge but it seems as if all is well.

I have to say the barnacle buster is addicting. I can’t wait to flush out the mains. Only thing is west marine has the pre mixed bottle for $70/gal. I’ll need 20 gallons for each engine. I can’t imagine it’ll really cost that much.
Try HD "Kleen Strip Concrete and Metal Prep" - its 40% Phosphoric acid so you dilute it down to 20%. Its about $20 per gallon...
 
Started up at 1130pm and a ton of mud, dirt shot out immediately followed by white particulate then a lot of white foam. Ran great but I thought I noticed excessive smoke. Couldn’t tell if it was from the high humidity level or if it was from shining a spot light directly into the exhaust so I shut it down.

The white foam and junk makes me think you got the HE cleaned out!
 
Started up at 1130pm and a ton of mud, dirt shot out immediately followed by white particulate then a lot of white foam. Ran great but I thought I noticed excessive smoke. Couldn’t tell if it was from the high humidity level or if it was from shining a spot light directly into the exhaust so I shut it down.

Fired right up this morning and zero smoke at all, temps seem to be about 10 degrees cooler and so far so good.

Any idea what the oil pressure should be while running? I can’t find it anywhere in the manual. The dummy gauge goes from 0-20-23-65-100. I’d say it’s fluctuating between 40-65 but who knows on this gauge. It’s to the right of middle visually on the gauge but it seems as if all is well.

I have to say the barnacle buster is addicting. I can’t wait to flush out the mains. Only thing is west marine has the pre mixed bottle for $70/gal. I’ll need 20 gallons for each engine. I can’t imagine it’ll really cost that much.
Get the concentrate. I think you mix 4-1.
 
Started up at 1130pm and a ton of mud, dirt shot out immediately followed by white particulate then a lot of white foam. Ran great but I thought I noticed excessive smoke. Couldn’t tell if it was from the high humidity level or if it was from shining a spot light directly into the exhaust so I shut it down.

Fired right up this morning and zero smoke at all, temps seem to be about 10 degrees cooler and so far so good.

Any idea what the oil pressure should be while running? I can’t find it anywhere in the manual. The dummy gauge goes from 0-20-23-65-100. I’d say it’s fluctuating between 40-65 but who knows on this gauge. It’s to the right of middle visually on the gauge but it seems as if all is well.

I have to say the barnacle buster is addicting. I can’t wait to flush out the mains. Only thing is west marine has the pre mixed bottle for $70/gal. I’ll need 20 gallons for each engine. I can’t imagine it’ll really cost that much.

My generator runs in the low 50's for oil pressure.
 
Generator ran absolutely perfect today. Upon further review I know exactly why all this happened. At low tide I turn up mud, and I don't mean dirty water, I mean lose steering props digging in the mud. If I was just moving forward I might be OK, but needing to pivot to get out of the end of our dock with port in fwd and starboard in reverse I am positive the generator sucked some major mud as the boat was spinning and turning up all the mud. Hopefully the engines are fine. Worst part is coming back this afternoon it was an even lower tide and I turned up a ton of mud again.

The other thing, when I checked out the generator strainer the screen basket was pretty clean but the water in the strainer itself was like clay. I could have done pottery with the stuff that came out when I put the hose in there and cleaned and blasted the strainer and seacock clean.

After letting the barnacle buster sit for about 5 hours when I started up the generator the stuff that exploded out of the exhaust was epic. It was literally like explosive diarrhea.

All of this reminded me of @mrsrobinson and the over heating issues he had with going through some mud as well.

Overall a great day out on the boat today and now I'm so excited to use barnacle buster on the engines. I won't do the closed loop thing but rather mix up about five 5 gallon buckets and start the engine and let it suck the stuff through the strainer. After the 5th bucket I'll shut the engine off and let it sit for 5hrs. Not as good as the closed loop flush but it'll have to do. There is a youtube video of doing this in a 48 MY with the QSM11s.
 
...Upon further review I know exactly why all this happened. At low tide I turn up mud, and I don't mean dirty water, I mean lose steering props digging in the mud. If I was just moving forward I might be OK, but needing to pivot to get out of the end of our dock with port in fwd and starboard in reverse I am positive the generator sucked some major mud as the boat was spinning and turning up all the mud. Hopefully the engines are fine...

I know that it's not always easy to connect all the dots, but this is very important piece of info that sets totally different direction in the troubleshooting process.

Hopefully, the engines are fine. But years ago, a friend had the same situation which resulted in a major job cleaning up all the systems. Genny shutting down was the least of the problems. Digging clams and sucking up the mud should not be taken lightly. It's never good and usually comes with some sort of a "penalty".
 

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