Odd Onan Quiet Diesel Behavior

[gumpy]

My new-to-me generator arrived this week. This spring I stumbled across an Onan 7500 watt Quiet Diesel generator that had just been listed on Craigslist in CO. It had been salvaged from a high end S&S that a couple from Ohio had bought and were on their maiden voyage when the wind blew them off the interstate. They hit a tree and demolished the motorhome, killing the husband. The motorhome had less than 4000 miles on it. So basically, the generator was brand new. I paid about 2/3 of what a new one would cost.

My in-laws picked it up and brought it to me when they came up this week. There was some minor damage to it. The air cleaner housing was busted, and there's a crack in the frame. I already had ordered parts for the air cleaner, so I was replacing that. I had to take the covers off the top and sides to gain access (and a few other tricks to actually get it replaced). Anyway, after blowing the grass and dirt out of it, I hooked up a battery and fuel lines to a can of diesel, and started it up. Purred like a kitten, but I noticed as it warmed up and I put a load of about 1500 watts on it, it started to smoke. Looked like unburned diesel bluish grey smoke. Seem like quite a bit of smoke, too.

So, I ran it again yesterday, and the same thing happened. I checked the temp at the water outlet nd radiator with my laser gun, because without the housing, there's no cooling capability of the radiator. When I saw it getting above 200*, I shut it down and put the side and top panels back on. After I got the enclosure put back on, I started it up again. Interestingly, there was no more smoke. I loaded it up to about 2500 watts, and it was perfectly clear.

Anybody care to venture a guess as to why it smokes when the enclosure is off, but doesn't smoke when the enclosure is on?  The enclosure is necessary to get air to flow over the radiator as it exits through the bottom. When it was off, no air could be forced over the radiator, so it heated up to 200 in just a matter of about 5 minutes. Of course, with the enclosure, I can't get a reading of the temp, and there are no gauges on this unit, only a sender and a lighted switch that's supposed to blink when it overheats and shuts down (which it never did because I didn't let it get that hot).

Anyway, I feel much better about my purchase. Now to get my batteries moved and get it installed before the end of July.

craig

[Nick Badame Refrig/ACC]

Hi Craig,

?? Hummm..

Do you think the gen was up side down in the crash?  and maybe lots of engine oil in the intake?

When my belt failed in my Onan 12.5, it overheated but the internal limit shut it down before damage happened. [no smoke]

Possibly  a stuck injector??

Anyway, all seems fine now so, good purchase man..  I also paid 1/3 of the sale price with my gen and had to drive to Kentucky to PU..

Good Luck
Nick-

[TomC]

Quite possibly when the cabinet is shut the fan creates a positive pressure inside which makes for a mild super charging effect.  The might be enough pressure to keep the oil on the other side of the piston rings causing the blue smoking to stop.
You know that this is an inverter generator, and the engine runs from 1500-2500rpm depending on the load?  One person I know had one and replaced it since he could never get used to the variable speed and it always woke him up when the A/C would come on.  But hopefully, such rpm changes will not bother you-I know it would bother me.  Good Luck, TomC

[TomCat]

It's a little early in the day to be drinking, eh Craig? 

Jay
87 SaftLiner

[lesrMC9]

Hi Craig; you said the magic words "HOT" --- when engines get hot the oil also get hot and thins out way to much getting sucked past the rings and burns!!
A car I was driving overheated before I got it to the side of the road it smoke like a forest fire, when coolant was replaced no more smoke when cool.
Les R MC9

[gumpy]

I considered that it might have been on it's side for awhile when it was wrecked. I suppose it's possible that there was some oil in the manifold. I ran it probably a total of 15 minutes on three
runs and it didn't clear, but when I put the shroud back on, it cleared instantly.

I suppose the thin oil or positive pressure thing is possible. Good theory, anyway, but no way to test it.

I guess I'll just chalk it up to experience... don't run the engine without the enclosure that's supposed to be there, and it won't smoke at you. 

Can't wait to get this puppy installed. I know it's variable speed depending on load. I don't think it's going to be much of a problem. Not very often do we need the a/c at night, and usually then we're in a cheap (as in free or $5) campground with electric. Still, I want the option to run off the gen when we can't find the cheap campground and have to use a Walmart or other parking place.

Thanks for the ideas.

craig

[Utahclaimjumper]

Those enclosures are engineered to place the air correctly around the engine and prevent localized hot spots on cylinders and such.>>>Dan

[Charles in SC]

I do not know why but mine smokes when the fuel filter needs changing. The filter is very restrictive even when clean. It does not take much to clog it. In a job long ago when we had a new truck come in we always had a problem with junk in the fuel tank stopping up the filters a couple of times in the first few thousand miles. You do have a fuel return line hooked up don't you. I think that would make a difference. Good luck and let us know what happens!

[gumpy]

Yeah, I put two lines on, and put them both in a 5-gallon can of diesel. No restrictions, other than the filter. I doubt the filter is
clogged, unless some insect got in it while it was sitting, which is unlikely due to the diesel being in there. It came out of a motorhome with less than 4000 actual miles on it, so I doubt it's been run even 20 hours.

The smoke was definitely related to having the exterior cover off. I'm sure it must have been heat related, but I can't explain it.

[HB of CJ]

Quick guess here is that somehow with the enclosure on, the mill may be starved for air, which may result in too much fuel which may result in the exhaust smoke?  Dunno. Obviously I'm missing something.