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Old 08-25-2010, 06:26 AM   #1
g1g
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Default Onan genny help

When I was on my last trip to Tennessee it was very hot 100+ . There were a couple times I run the genny so I can run the AC. All was fine for a while but I would say after about an hour the genny would stop. Then it would be hard to restart and it would die in a couple minutes anyway. After leaving it set for a while maybe to cool off I really don't know, I could start it and it would run fine for about an hour and the same thing would happen. I ran the genny for several hours before and after my trip while at home in Ohio and it was fine. Any Ideas on why it stopped?
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Old 08-25-2010, 02:47 PM   #2
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Default Re: Onan genny help

Check your oil level. Alot of Generators have a low oil shut off. When the unit gets real hot and the oil viscosity starts to break down the oil pressure drops and the unit safety measure(low oil) kicks in and will not start till oil pressure goes up(oil cools)..........Mike
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Old 08-29-2010, 02:47 AM   #3
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Default Re: Onan genny help

That was my first idea and upon checking it let's just say it was 3/4 up in the safe zone or down just 1/4 into the safe zone whichever way you want to describe it. I have Mobil 1 20w50 in it just for that reason. Could down just that little bit make the difference?
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Old 08-29-2010, 11:38 PM   #4
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Default Re: Onan genny help

No, being down only a 1/4 from full shouldn't cause the low oil safety sensor to activate. I ran mine on my '99 American Cruiser yesterday at approx 90 degrees in the shade(and there wasn't any) with 158 hr on the clock. Ran it for 2 hours with air on high plus the stereo. Hit the micro to see if it would hiccup but it just ran fine. Is your air filter sealed up tight. You could get a vapor lock from heat buildup at the carb if the air cleaner isn't sealing. Wish you luck.........Mike
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Old 08-30-2010, 03:53 AM   #5
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Default Re: Onan genny help

I installed a new generic electric fuel pump about 1 1/2 years ago on the outside of the houseing. I didn't think you could get vaporlock if the fuel pump is before the heat since it is all pressurised going into the carb. Also as I think about it when I was trying to restart it I mentioned it was hard to start but If I remember right I don't think it was cranking over as fast as when it is cold. I think I will also check the fuel filter but in reality I don't think it has 10 hours on it. I have heard so much on the low oil sensor but like I said it really isn't down that much but I sdidn't know if it had to be full and it's synthetic. This is a bit of a puzzler , thats why I am asking for suggestions. I also want to thank you for your help too. Could oil being down just that little bit combined with 100 deg plus temp cause this? Could there be an overall temp sensor in there to shut it down, but that is really when I want the AC to run.
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Old 08-30-2010, 01:22 PM   #6
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Default Re: Onan genny help

20-50W synthetic oil should be more than sufficient in weight to run at 100 degrees F+. In fact I'd say it was a perfect weight to run at those temps. Perhaps your Gen set just needs to be run more to break it in/clean it out. These generators that run on gasoline need to be run 2 hours a month under load to stay at peak performance. If the unit is around 2 years old it should have 50 +- hours on the meter. I'm grasping at straws as I really don't have an answer. Maybe there's someone else out there that has a few suggestions? Anyone...............Mike
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Old 08-30-2010, 03:33 PM   #7
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Default Re: Onan genny help

When mine died completely back in February, it was a connector on the starter solenoid
which had corroded and fell off. It's inside the casing, on the opposite side from the
exhaust system and tailpipe. If you're standing behind and looking at my van, it would be
towards the front and on the left side.
Anyway, they had to drop the genset and remove the green cover to get at it. The service
guy was able to solder a new blade on the old solenoid, and replaced the wire. Fixed!!!
He said one of the biggest problems is that folks just don't run their gensets enough to heat
them up and get rid of the condensation which forms inside the cover, which was probably
what caused my corrosion problem. In this case, heat is a good thing!

Heat isn't always a good thing, though.
I owned a '73 Mustang Convertible, 351C, 4 barrel, headers, mags, air shocks in the rear end,
all the goodies I could add. It was canary yellow, with the Mach 1 stripe/decal kit in black.
A real beauty!!!! It was the "trade-in" for my first camper van
back in the late 70s. In hindsight, I should never have let her go.

For a while, I had the same problem with it, that your genset seems to have. It would start
fine when cold, but eventually, if I turned it off and then tried to restart it, it wouldn't turn over
or sounded like the battery was near dead. If I let it sit for a while and cool down, and then
tried it, it fired right up.
One time when it happened, I popped the hood and was checking the battery for a loose cable
connection. I jiggled the wire to the starter motor, and my friend turned the key, and it fired up,
but it stalled. I tried jiggling it again then put some tension on it, and we tried again and it
fired up and kept running. Getting down underneath it, I could see that the cable connection was
slightly loose on the starter motor casing.
But why?
Well, it seems that when the engine was cold, the threaded bolt/post on the starter motor
was fully expanded, and the standard nut holding the eyelet connector on the battery cable
in place was tight. Engine starting was no problem.
However, when the engine heated up (the starter was close to the exhaust pipe) either the post/bolt
would also get hot, and contract just enough, or the nut also heated up and expanded just enough,
that the connection got loose and electrical connectivity was lost.
The fix was adding a locking nut to keep the battery cable tightly connected to the starter motor.
MORAL: Nuts and bolts expand and contract when exposed to extreme temperature changes,
and can loosen, resulting in a loss of electrical connectivity.

Is there any chance the connections from the battery are loosened when your genset has run for a
while and heated up? Maybe you need to check all your cable connections for a loose one, after it's run
for a while. I'd start with the connections at the auxilliary battery(s) and work towards the ones at the
genset.

Sorry for the long story,
good luck.
Mike.
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Old 08-31-2010, 06:08 AM   #8
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Default Re: Onan genny help

I never even thought of a loose cable. The battery is clear of the genny but the other ends or even ground may be a bit loose as you suggested. I definatly will check that. As for excersing it for 2 hours a month, lets just say Im a bit lax on that or more lke grossly lax. I go for several months without starting it at all. It usually is hard to start and keeps dying on me for a while when I excercise it because it should have been done months ago. After I run it for an hour it does run better.
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Old 08-31-2010, 12:38 PM   #9
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Default Re: Onan genny help

Just after we bought our van (2 years ago now) I had intermittent genset starting and run
problems with mine. There's a thread on here about it. Bit lengthy, but lots of good PD/PR info.
viewtopic.php?f=9&t=1014
markopolo suggested a loose connection somewhere, and after eliminating any other
causes, turned out to be the culprit. One of the connections on one aux battery cable had
corroded inside the cable insulation, and was flaky. I cut the cable about an inch
shorter, and replaced the eyelet connector at the battery end, and that fixed it.

Check the connectors on the cable ends, and make sure they are securely clamped down on the cables.
If you have to give each one a good hard pull, or wiggle it, to make sure it's solidly attached, do it.
They're easy to replace and it'll save you hassles later.
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Old 09-01-2010, 06:05 PM   #10
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Default Re: Onan genny help

Look for a vapor-lock situation. If you have a loose connection/electrical problem the unit should not ordinarily "run for an hour or two", it would be more of a go/no go situation. Always a good thing to check/clean all grounds and cable connections.
Could also be a dirty fuel filter or failing fuel pump.
Sometimes the ignition module or the condenser can be affected by heat.
Bon Chance
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