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Old 08-21-2020, 07:54 PM   #15
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Hard to believe rust could be the culprit, unless of course it was run on distilled water.
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Old 08-21-2020, 08:00 PM   #16
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I had similar problems with my 7.5k everything was replaced that you did except I see they didn't replace the radiator and that's fix my problem
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Old 08-21-2020, 08:47 PM   #17
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Hoses do collapse internally, I didn't see any mention of them being replaced? Or did I miss it? Also too much fuel will cause a diesel to run hot.
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Old 08-21-2020, 09:24 PM   #18
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Exhaust blockage was mentioned, it has a spark arrestor I believe... has it been cleaned. Did you get your old radiator back. I would hate to do an engine flush on a new one.
Spent a bunch of time once for an upside down thermostat.
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Old 08-21-2020, 11:09 PM   #19
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Couple of options (that sort of depend on what the blockage consists of):

1). If you suspect the blockage is something other than rust: Go to a pool supply store and buy a couple gallons of muriatic acid. Disconnect the drained engine block from the hoses, plug the lower openings, and pour the acid in and let it sit for an hour, and then drain it and flush it several times. This will work if the blockage is sediment or precipitate or just basic chemical sludge. (If you have some sort of part that has slipped inside and is blocking things, this won't help. But it won't hurt, either.) Nasty stuff to work with - it's a strong acid - gloves, glasses, flush everything clean.

I wouldn't do this to a new engine, but I've rescued dying engines with it.

2). If you think rust is the culprit, Evapo-rust makes an engine block de-ruster they call Thermocure. Like the acid, you pour it in and let it sit for a specified time. Does a nice job of cleaning out rust blockages. Again, flush thoroughly. Multiple applications work best.

If you can find out from the tech what the radiator blockage seemed to be made of - rust or gunk - you can choose one of the above options. If no one knows, I'd start with the Thermocure. https://evapo-rust.com/thermocure/


(Rust blockage is what happens when people run engines with water instead of antifreeze.)
Thanks Bobby! Iíll try to contact the radiator shop that diagnosed the ďblockageĒ for Cummins and see if I can get the radiator back to inspect or ask them if they can tell me either way. This sounds like my best option at this point
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Old 08-21-2020, 11:10 PM   #20
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I had similar problems with my 7.5k everything was replaced that you did except I see they didn't replace the radiator and that's fix my problem
The radiator is the last thing done and it didnít fix it unfortunately
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Old 08-21-2020, 11:11 PM   #21
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Hoses do collapse internally, I didn't see any mention of them being replaced? Or did I miss it? Also too much fuel will cause a diesel to run hot.
I inspected the hoses and didnít see any issues. Cummins also inspected the hoses. None have been replaced however. Might be next thing I look into
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Old 08-21-2020, 11:12 PM   #22
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Exhaust blockage was mentioned, it has a spark arrestor I believe... has it been cleaned. Did you get your old radiator back. I would hate to do an engine flush on a new one.
Spent a bunch of time once for an upside down thermostat.
I cleaned the spark arrestor when I did the other maintenance. I forgot to mention that, thanks for reminding me. But Cummins confirmed for me that there is nothing wrong with the exhaust system
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Old 08-22-2020, 12:14 AM   #23
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The more I think of this, the more I think you should just skip the acid step for now and go right to a rust-removal flush. If you had an actual blockage, I doubt it would run at any output level for long. I'm guessing you have a coating of rust in the jackets - which acts as a great insulator and slows down heat exchange and which would do what you're describing.

If the radiator is blocked, that would likely be with rust particles that have flaked off inside the engine and flowed out. Rad has much smaller passages.

And, just to be clear - flush with Thermocure or with acid only with the engine disconnected from hoses, radiator, thermostat, everything, 'cuz they'll never be the same if you run this stuff through them.
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Old 08-22-2020, 06:28 AM   #24
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When I acid clean heat exchangers systems and large recip. compressors at work we use a remote air pump. Drum of acid and water . Pump from bottom to top to remove air. Then we shut off valves on hoses and swap camlock PT connectors to drop out/down sediment. Depending on size I'll do water first to bleed air the add acid, drain, flush and neutralize. A fair amount of heat will speed the process.
Seems strange to me it supposedly ran at 90% outside of MH, I'm sure it breathes better that way , there isn't some sort of air dam / shroud missing ???
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Old 08-22-2020, 09:41 AM   #25
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The more I think of this, the more I think you should just skip the acid step for now and go right to a rust-removal flush. If you had an actual blockage, I doubt it would run at any output level for long. I'm guessing you have a coating of rust in the jackets - which acts as a great insulator and slows down heat exchange and which would do what you're describing.

If the radiator is blocked, that would likely be with rust particles that have flaked off inside the engine and flowed out. Rad has much smaller passages.

And, just to be clear - flush with Thermocure or with acid only with the engine disconnected from hoses, radiator, thermostat, everything, 'cuz they'll never be the same if you run this stuff through them.
I think youíre right. Iíll do the thermocure treatment next chance I get. And thanks for the heads up on the thermostat, you mentioned radiator and hoses before, but I probably wouldnít have though about removing thermostat. Is the temp sensor okay to stay in?
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Old 08-22-2020, 09:44 AM   #26
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When I acid clean heat exchangers systems and large recip. compressors at work we use a remote air pump. Drum of acid and water . Pump from bottom to top to remove air. Then we shut off valves on hoses and swap camlock PT connectors to drop out/down sediment. Depending on size I'll do water first to bleed air the add acid, drain, flush and neutralize. A fair amount of heat will speed the process.
Seems strange to me it supposedly ran at 90% outside of MH, I'm sure it breathes better that way , there isn't some sort of air dam / shroud missing ???
Well after they replaced the radiator they said it was overheating on the bench so I grilled them about their ď90% load testĒ before because no way would replacing the radiator make it worse. They side stepped the question to no end which lead me to believe they didnít really test it as hard as they said they did, because now it is in fact still overheating outside the chassis. So I think they just fed me some bologna earlier on about the outside chassis 90% load test.
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Old 08-22-2020, 10:03 AM   #27
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Although I don't have the same generator, I have the shutdown issue as well. I was in a shop with a friend the other day and asked if they speak Onan generator specifically, and told them my problem. Right away one of them said, Circuit Board. They has just fixed the overheat and shutdown issue with another generator. So, my next step is to buy another circuit board and try it. After thinking about it, it does make some sense. Expanding, contracting, and those parts working until they loose contact, I guess, lol.
Worth a shot. You have spent a bunch of money already. I wouldn't think a circuit board would cost much. JMHO. Good luck.

PS. Of course I will be looking in to see how your situation pans out.
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Old 08-22-2020, 10:15 AM   #28
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Although I don't have the same generator, I have the shutdown issue as well. I was in a shop with a friend the other day and asked if they speak Onan generator specifically, and told them my problem. Right away one of them said, Circuit Board. They has just fixed the overheat and shutdown issue with another generator. So, my next step is to buy another circuit board and try it. After thinking about it, it does make some sense. Expanding, contracting, and those parts working until they loose contact, I guess, lol.
Worth a shot. You have spent a bunch of money already. I wouldn't think a circuit board would cost much. JMHO. Good luck.

PS. Of course I will be looking in to see how your situation pans out.
If I was still diagnosing this one myself I would certainly try a circuit board. But my generator is with CUMMINS and theyíve had their computers and load banks hooked up to it this whole time so Iím sure they would know if the circuit board was faulty. Plus, temp guns have verified that the unit is in fact overheating. Thanks for the suggestion though, and Iíll keep this info in my back pocket for the future
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