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Old 11-17-2012, 06:26 PM   #1
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Onan Generator oil usage question

We have a 1995 Onan 4.0KY generator that is using some oil, the aircleaner housing is oily, (inside), so I think the engine with 1753 hours has worn rings, or maybe valve seals. I do have some knowledge of building V8 Mopars, from the ground up, (hot rods), but not much experience on small engines. The engine runs great, but does blow a "little" blue (oil) smoke when started, then clears up. You have to be watching the exhaust to see it. (in my nature to pay attention to mechanical things before they get out of hand) ... I have not checked the spark plug , which I replaced when we bought the coach just over a year ago, but I will.
I found this great manual, http://www.cumminsonan.com/www/pdf/manuals/981-0503.pdf But I guess my question since I'm ready to change the oil "again" for the winter storage, is there a oil such as synthetic or such
that would help prolong the inevitable of rebuilding the engine ? As much as I hate to, I guess I'll pull the generator out enough to clean things up, and change the fuel filter and fuel line. It's not bad enough to warrant rebuilding the engine, which I would do myself. Guess I'm looking for a 'bandaid'...
We don't boondock, but we do make most of our trips out west in the hotter months, so we use the genny for ac... Thanks very much ,
Monkey
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Old 11-17-2012, 06:45 PM   #2
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Hi Monkey,

I have been using Mobil 1 10w30 fully synthetic in my Onan 7.0 generator.

Jon
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Old 11-17-2012, 06:58 PM   #3
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Hi Monkey,

I have been using Mobil 1 10w30 fully synthetic in my Onan 7.0 generator.

Jon
Thanks Jon, but this is a high hour unit,, that I do believe was well taken care of by the original owner,, coach in great shape for a 95, my question there as I have never used synthetic, is the Onan manual says 10W30 is only good to use up to 80 degrees, which it is that at 6am in AZ ..... ? Could a heavier weight synthetic prolong my rebuilding and use it in hot weather ? Thanks again, Monkey
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Old 11-17-2012, 07:00 PM   #4
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Sounds like the crankcase oil breather return to the air filter is returning excess oil vapors - either too-high oil level, or - as you suspect, worn parts allowing blowby. I doubt any plain oil brand change will "correct" worn parts, but I *have* successfully used STP to improve ring sealing and various associated worn engine symptoms. Not a cure, but a method to extend useful life until a better solution can be applied...

All you've stated so far, is oil in the air filter, and light blue smoke at startup - is that it - or is there actually oil usage?

{I'll duck and run now, before the "Snakeloil" crowd jumps in...)
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Old 11-17-2012, 07:18 PM   #5
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Sounds like the crankcase oil breather return to the air filter is returning excess oil vapors - either too-high oil level, or - as you suspect, worn parts allowing blowby. I doubt any plain oil brand change will "correct" worn parts, but I *have* successfully used STP to improve ring sealing and various associated worn engine symptoms. Not a cure, but a method to extend useful life until a better solution can be applied...

All you've stated so far, is oil in the air filter, and light blue smoke at startup - is that it - or is there actually oil usage?

{I'll duck and run now, before the "Snakeloil" crowd jumps in...)
Thanks Gary, There is actual oil usage, although I can't say exactly how much... Last trip we ran it more than ever,,, maybe 20 -25 hours, and it was about 1/2 qt low. (1.6 qts total fill) The entire left end of the engine (air cleaner end) is drenched with oil, I have not cleaned that since we owned it. So yes I believe as you said partly at least it's coming from the crankcase. The valve cover is not leaking, so it's internal wear, which is why I asked about oils and our treatments. Thanks for your suggestion on STP... I appreciatte the idea's !!!
And no, not excessive oil levels,, I pay real close attention to things like that. I might add again this was in summer AZ heat,,, 100 degrees ++
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Old 11-17-2012, 07:27 PM   #6
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Thanks Gary, There is actual oil usage, although I can't say exactly how much... Last trip we ran it more than ever,,, maybe 20 -25 hours, and it was about 1/2 qt low. (1.6 qts total fill) The entire left end of the engine (air cleaner end) is drenched with oil, I have not cleaned that since we owned it. So yes I believe as you said partly at least it's coming from the crankcase. The valve cover is not leaking, so it's internal wear, which is why I asked about oils and our treatments. Thanks for your suggestion on STP... I appreciatte the idea's !!!
And no, not excessive oil levels,, I pay real close attention to things like that.
The air cleaner end of the engine is drenched with oil. Makes me ask if you've checked the crankcase ventilation valve.
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Old 11-17-2012, 07:28 PM   #7
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The air cleaner end of the engine is drenched with oil. Makes me ask if you've checked the crankcase ventilation valve.
I have not,,, the way I see it on the pdf, is I need to pull the valve cover to get to the reed valve,,, is that correct ???
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Old 11-17-2012, 08:02 PM   #8
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You can use synthetic if you like but it isn't going to fix or prolong anything.

You can use 10W40 or 15W40 if temps will reach 100, but current Onan manuals specify that 10W30 is ok to 100 as well. The 40 weight might be better in an older engine, though.
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Old 11-17-2012, 08:24 PM   #9
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You can use synthetic if you like but it isn't going to fix or prolong anything.

You can use 10W40 or 15W40 if temps will reach 100, but current Onan manuals specify that 10W30 is ok to 100 as well. The 40 weight might be better in an older engine, though.
Thanks Gary, I was leaning towards a heavier weight oil,,, since we don't use it in cold weather,,, (unless we have another big ice storm here in Arkansas,,,, God forbid,,, ) At least now we would have hot running water !!! Anybody use Lucas oil products ??
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Old 11-17-2012, 08:41 PM   #10
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Run 20/50w for air cooled engine motorcycle synthetic oil in it.
I have for the last 10 years in my Onan 6.5 with no problem.
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Old 11-18-2012, 02:52 PM   #11
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Mobil 1 also makes a fully synthetic high mileage 10/40 w oil for engines with over 75,000 miles.

Jon
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Old 11-18-2012, 04:27 PM   #12
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Mobil 1 also makes a fully synthetic high mileage 10/40 w oil for engines with over 75,000 miles.

Jon
Thankyou Jon,,, I didn't know that, and will look in to it...
Monkey
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Old 11-21-2012, 06:50 PM   #13
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if you want to see how bad the rings are, try taking the oil filler cap off when running and see how bad she's blowing.
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Old 11-21-2012, 06:59 PM   #14
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monkey---was just on ebay they have a onan ky motor they took off a generator. they say low hour buy now price $299.99
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