onan 800 generator smoking

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puff501

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Feb 13, 2018
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we have an onan 8000 generator.  the generator starts well and smokes at first with no load but clears up in 5 to 10 minutes.  then we put it under load and it smokes a lot and keeps smoking and once we take the load off it, it clears up.  back under load smokes a lot again.
white smoke.  is this engine toast?  it has about 8000 hours on it.
 
    Assuming this ia a gasoline generator then white or bluish smoke indicated rings. Has this generator been sitting for a long time? Sometimes the cylinders will get a coating of light rust that will keep the rings from seating. Often it will clear up with continued use.
  Check you oil for the presence of gasoline, if the conditions are right the oil can become diluted with gasoline, thinning it out and leaking past the rings and valves.
  Otherwise my bet is on a worn out ring set.
 
catblaster said:
    Assuming this ia a gasoline generator then white or bluish smoke indicated rings. Has this generator been sitting for a long time? Sometimes the cylinders will get a coating of light rust that will keep the rings from seating. Often it will clear up with continued use.
  Check you oil for the presence of gasoline, if the conditions are right the oil can become diluted with gasoline, thinning it out and leaking past the rings and valves.
  Otherwise my bet is on a worn out ring set.
Click to expand...

All the 8000 watt gennys I could find were diesels. I'm with Roy, 8000 hours, rebuild time.

If anyone has a gas Onan series B,P, or CCK, that needs rebuilding, I can give you contact info for the best in the Americas to get it rebuilt. He's not the cheapest, but also not a price gouger(sp). It will come back to you better than new.
 
thanks everybody.
you all seem to be coming up with the same idea that i had.  maybe rebuild time
and yes its a diesel.
and yes it is white smoke and thick at times.
im going to change the oil this weekend and check it out.  if its still chugging, i just may open it up and do a compression test.  we will have to decide either tear it down for rebuild or just start looking for a new one.
thanks again all
 
Most Onan 7500/8000 gensets use a Kubota 3-cylinder diesel, and that engine is used in a lot of things. There are a large number of YouTube videos on Kubota engine overhauls and parts are readily available from what I see & hear.

But I'm not sure you need that, or at least it is still up for debate. White smoke isn't necessarily a major problem and the fact that it occurs under load could mean that the engine speed governor isn't working properly.  The Onan 8000 diesel is an inverter/generator so both engine rpm and power is controlled to produce the desired level of wattage (load).  I would also clean or change the air filter and replace the fuel filter before making any  hasty decisions.

Does the engine respond with more power when the load comes on, or does it stumble and just smoke more?
 
Change the fuel filters first, if they have any water droplets in the fuel it will cause this on a diesel.  Is it hard to start?
 
Before you get too excited do a compression check and note any differences in the readings between cylinders.  I wonder if you have coolant leaking which would give white smoke.
 
Gary RV_Wizard said:
Most Onan 7500/8000 gensets use a Kubota 3-cylinder diesel, and that engine is used in a lot of things. There are a large number of YouTube videos on Kubota engine overhauls and parts are readily available from what I see & hear.

But I'm not sure you need that, or at least it is still up for debate. White smoke isn't necessarily a major problem and the fact that it occurs under load could mean that the engine speed governor isn't working properly.  The Onan 8000 diesel is an inverter/generator so both engine rpm and power is controlled to produce the desired level of wattage (load).  I would also clean or change the air filter and replace the fuel filter before making any  hasty decisions.

Does the engine respond with more power when the load comes on, or does it stumble and just smoke more?
Click to expand...

Ths generator runs strong.  It starts right up and idles smooth.  I let it warm up and turn on the a/c's and it revs right up and again runs smooth.  Once the coach gets to temp, the a/c's cycle on and off and the generator responds right away, revving up or idling down as it should.  It does not use any anti freeze.  I can't remember the last time I added any coolant to it.  I have already changed the fuel filter and there has been no difference in operation.  It still runs great.  Just a ton of smoke. 

I changed the oil and I also put a half a bottle of Lucas oil treatment in it.  It's still smoking but I would say it is a 70%, just a guess, decrease in smoke under load.  But it seems to me there is still too much smoke to run it in a public place like a parking lot or campground or anywhere there are people around close by.  Some folks may call the environmental cops on me.
And there is no smoke at no load.
There is still smoke at initial start up with no load but it clears out in 5 minutes or so.

I'm going to let it run for a couple days straight and see how long it lasts or if it gets any better.
I haven't changed the air filter yet.  Only reason I haven't changed the air filter yet is because it runs so good I thought it was breathing just fine.
I'll also take a video of it and put it up in this post.  I kind of wish I took one before i change the oil.
Thanks again all.
 
No profile so do not know if gas or diesel
What color is the smoke
Mine used to smoke at first.. Till I had the oil professionally changed (NOT THE PROBLEM)
But once it had run for a minute or so it cleared up
When the tech went to start it after changing the oil, he noticed a sticky choke (Gas engine) and that WAS the problem.  No charge (included in labor for oil change)

You might need a ring job

Color of smoke and check exhaust pipe of oily residue and report back on what you find. Others are better at diesels.  I am "Medium" on gas.. Neither expert nor novice.
 
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