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12.5 Onan randomly shuts down. NO CODES. Grass/weeds blocking air intake.


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I do not have a 12.5 Onan.  But on a trip to Quartzsite a few years ago, one of my friends had a problem with his 12.5 Onan genny in a 2011 Camelot shutting down for no apparent reason.  It NEVER threw a code.  Since we were dry camping in the desert, that was a distressing problem.  In desperation, my friend called an Onan/Cummins field service technician.  The tech could not read any error codes.  We tried running the genny with no load, and with all three AC units operating for a sustained (30 minute) period.  It performed perfectly.  Grabbing at straws, the tech replaced the control board for the genny.  No disrespect to the tech--he had no idea what was wrong and neither did any of us tech-savvy folks.  As you might suspect, that did not fix the problem, even though the total cost was about $1250.

Long story short--it was grass and weeds caught up in the air intake grill under the genny.  Why did it never throw an overheat code (even with the new control board)?  I have no idea.  But my friend constantly checks his air intake now.

I mention this because it is something ANYONE can check.  It might not be your problem...but it might.

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I think it did not throw an overheat code because the air intake opening is just for that, the air intake. It is also sucking air from the side so it might have played a roll? Since the intake does not go through radiator, cooling might have been still functional. I will be much more sensitive to where we park it and throw a rag under the generator when in dirt or grass. Good point Van.

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I'm going to have to slither under there and see this intake hole.

So unless I've got this wrong, this 4" intake feeds the engine, the engine cooling system, and the generator cooling?

After reading Ivan's post today, I fired up my gen with the maintenance cover off, and plenty of air coming from the generator fan. 

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With the 12.5, these are the openings,  the large round one at bottom is for the windings air cooling (I just put a grill on it), the oval and smaller one is engine air intake. Engine cooling goes through the radiator. There is an other big fan at the back of the engine (really the front of it in automotive sense, where the pulleys are) that blows all that hot air from the case out back and down. Hope it helps.



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