Home » Public Forums » GMCnet » Intermittent Onan Revisited
| Intermittent Onan Revisited [message #188194] |
Thu, 25 October 2012 09:48  |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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Back in July, I was on here talking about a problem with my Onan. It would run for a certain amount of time and then quit, only to start and run again after it cooled down. The interval of time it would stay running was diminishing from about 1.5 hours down to only about 20 minutes. I thought it might be caused by low oil pressure, since I had just changed the oil to 30w that seemed to thin down considerably when hot. That wasn't it. I considered the ignition system, but it would start and run, very briefly, after these incidents, so it seemed to be getting spark.
Finally, on the advice of a mechanic friend, I decided to replace the fuel pump, which seemed to be fine, but did not seem to be pumping fuel (although it still 'ran') when it got too hot. I ordered a new pump from Jim K and installed it. On our trip last weekend, we ran the Onan and the AC from North Tucson to Willcox, about an hour and a half. It never faltered. It seems the fuel pump was the problem. It seems weird that it would not pump when hot, since it still made the expected noise that it makes while running. The only difference was that the tone did not change as it built up pressure, as it would when it was cold.
I know Rob M. and others, were experiencing similar symptoms from THEIR Onans and I think a new pump will cure the problem.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Intermittent Onan Revisited [message #188199 is a reply to message #188194] |
Thu, 25 October 2012 10:32  |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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| Carl S. wrote on Thu, 25 October 2012 09:48 |
Back in July, I was on here talking about a problem with my Onan. It would run for a certain amount of time and then quit, only to start and run again after it cooled down. The interval of time it would stay running was diminishing from about 1.5 hours down to only about 20 minutes. I thought it might be caused by low oil pressure, since I had just changed the oil to 30w that seemed to thin down considerably when hot. That wasn't it. I considered the ignition system, but it would start and run, very briefly, after these incidents, so it seemed to be getting spark.
Finally, on the advice of a mechanic friend, I decided to replace the fuel pump, which seemed to be fine, but did not seem to be pumping fuel (although it still 'ran') when it got too hot. I ordered a new pump from Jim K and installed it. On our trip last weekend, we ran the Onan and the AC from North Tucson to Willcox, about an hour and a half. It never faltered. It seems the fuel pump was the problem. It seems weird that it would not pump when hot, since it still made the expected noise that it makes while running. The only difference was that the tone did not change as it built up pressure, as it would when it was cold.
I know Rob M. and others, were experiencing similar symptoms from THEIR Onans and I think a new pump will cure the problem.
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I got an email from Rob, but don't recall if he posted here, that he replaced his fuel pump and that fixed it for him too. I would have bet lunch money that it was the coil, but it wasn't.
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| Re: Intermittent Onan Revisited [message #188201 is a reply to message #188194] |
Thu, 25 October 2012 10:42 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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| Carl S. wrote on Thu, 25 October 2012 07:48 |
Back in July, I was on here talking about a problem with my Onan. It would run for a certain amount of time and then quit, only to start and run again after it cooled down. The interval of time it would stay running was diminishing from about 1.5 hours down to only about 20 minutes. I thought it might be caused by low oil pressure, since I had just changed the oil to 30w that seemed to thin down considerably when hot. That wasn't it. I considered the ignition system, but it would start and run, very briefly, after these incidents, so it seemed to be getting spark.
Finally, on the advice of a mechanic friend, I decided to replace the fuel pump, which seemed to be fine, but did not seem to be pumping fuel (although it still 'ran') when it got too hot. I ordered a new pump from Jim K and installed it. On our trip last weekend, we ran the Onan and the AC from North Tucson to Willcox, about an hour and a half. It never faltered. It seems the fuel pump was the problem. It seems weird that it would not pump when hot, since it still made the expected noise that it makes while running. The only difference was that the tone did not change as it built up pressure, as it would when it was cold.
I know Rob M. and others, were experiencing similar symptoms from THEIR Onans and I think a new pump will cure the problem.
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Back in the day I ran 2 of those Bendix pumps in parallel on my Olds powered ski boat. as they got older they pumped less and less gas especially when they warmed up but they kept on ticking making me think I had a different problem.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Intermittent Onan Revisited [message #188272 is a reply to message #188199] |
Thu, 25 October 2012 20:36 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Mark,
As Strother Martin said in Cool Hand Luke; "we seem to have a failure to communicate."
I bought the same fuel pump that is made by Facet to install in Double Trouble but never got round to it because as we headed north
it cooled off and it ran OK.
The very last time it died I immediately went out, opened the drawer, jumped 5 - 9 and the pump just pumped and pumped and pumped,
and pumped and NEVER slowed down or stopped.
I reckon that it's vapor locking.
The question becomes will the new one do the same thing?
The pump that Carl got from JimK is not the same as the OEM pump so we know that one works.
BTW the pump from JimK is made by Mr. Gasket and sells for $53; the one I got is made by Facet and sells for $93.
Regards,
Rob M.
-----Original Message-----
From: A.
Carl S. wrote on Thu, 25 October 2012 09:48
> Back in July, I was on here talking about a problem with my Onan. It would run for a certain amount of time and then quit, only
to start and run again after it cooled down. The interval of time it would stay running was diminishing from about 1.5 hours down
to only about 20 minutes. I thought it might be caused by low oil pressure, since I had just changed the oil to 30w that seemed to
thin down considerably when hot. That wasn't it. I considered the ignition system, but it would start and run, very briefly, after
these incidents, so it seemed to be getting spark.
>
> Finally, on the advice of a mechanic friend, I decided to replace the fuel pump, which seemed to be fine, but did not seem to be
pumping fuel (although it still 'ran') when it got too hot. I ordered a new pump from Jim K and installed it. On our trip last
weekend, we ran the Onan and the AC from North Tucson to Willcox, about an hour and a half. It never faltered. It seems the fuel
pump was the problem. It seems weird that it would not pump when hot, since it still made the expected noise that it makes while
running. The only difference was that the tone did not change as it built up pressure, as it would when it was cold.
>
> I know Rob M. and others, were experiencing similar symptoms from THEIR Onans and I think a new pump will cure the problem.
I got an email from Rob, but don't recall if he posted here, that he replaced his fuel pump and that fixed it for him too. I would
have bet lunch money that it was the coil, but it wasn't.
--
'73 23' Sequoia
UA (Upper Alabama)
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Intermittent Onan Revisited [message #188282 is a reply to message #188273] |
Thu, 25 October 2012 20:53 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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| Robert Mueller wrote on Thu, 25 October 2012 18:38 |
Roy,
Stay tuned to this channel for next year's installment - we'll be heading to Arizona then north!
Regards,
Rob M.
-----Original Message-----
From: roy@gmcnet.org
Back in the day I ran 2 of those Bendix pumps in parallel on my Olds powered ski boat. as they got older they pumped less and less
gas especially when they warmed up but they kept on ticking making me think I had a different problem.
--
Roy Keen
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It must be nice to follow the summer rather then try to find a warm spot when the frost sets in.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Intermittent Onan Revisited [message #188284 is a reply to message #188272] |
Thu, 25 October 2012 21:24 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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| Robert Mueller wrote on Thu, 25 October 2012 20:36 |
Mark,
As Strother Martin said in Cool Hand Luke; "we seem to have a failure to communicate."
I bought the same fuel pump that is made by Facet to install in Double Trouble but never got round to it because as we headed north it cooled off and it ran OK.
The very last time it died I immediately went out, opened the drawer, jumped 5 - 9 and the pump just pumped and pumped and pumped, and pumped and NEVER slowed down or stopped.
I reckon that it's vapor locking.
The question becomes will the new one do the same thing?
The pump that Carl got from JimK is not the same as the OEM pump so we know that one works.
BTW the pump from JimK is made by Mr. Gasket and sells for $53; the one I got is made by Facet and sells for $93.
Regards,
Rob M.
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You are correct. Not only do I have CRS, I seem to be creating stuff to fill in the blanks.
I went through my email after I posted that and found that all you knew was when it got hot, the pump would run, but did not appear to be moving any fuel. So you still didn't know if that behavior is unique to an aged Onan OEM pump or other pumps would behave that way.
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| Re: [GMCnet] Intermittent Onan Revisited [message #188300 is a reply to message #188284] |
Fri, 26 October 2012 03:40 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Mark,
I am glad you noted what you did below because as I typed my response I heard a little voice in my head saying "are you sure about
what you're writing?"
HOWEVER, since I bought the Facet "copy" of the Bendix pump we should be able to determine if the problem is related to the pump
design or age when the Facet is installed.
Unfortunately that won't happen until next June / July, assuming I am still in a vertical position! ;-)
Regards,
Rob M.
-----Original Message-----
From: A.
You are correct. Not only do I have CRS, I seem to be creating stuff to fill in the blanks.
I went through my email after I posted that and found that all you knew was when it got hot, the pump would run, but did not appear
to be moving any fuel. So you still didn't know if that behavior is unique to an aged Onan OEM pump or other pumps would behave that
way.
--
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Intermittent Onan Revisited [message #188344 is a reply to message #188300] |
Fri, 26 October 2012 14:06 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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The reason I didn't think it was vapor lock is that it would do it even if the outside temp was not very hot, and on a fresh gas fill-up. To me, cool gas and cool ambient temps ruled out vapor lock as the problem. Even though the pump would keep running, and would pump up enough fuel to momentarily restart, it would not change 'tone' or continue to supply the engine with an adequate amount of fuel to keep it running. That, and the fact that it WOULD start back up, and run for a few seconds, indicated that the ignition system was okay. At any rate, the fuel pump solved the problem.
BTW, all the work I did to stop oil leaks (gaskets, seals, etc.) seems to have paid off as well. There was no oil dripping from underneath after we got home. Maybe all the old residual oil finally has made it's way to the ground.
I love my Onan! 2,000 plus hours and still going strong.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Intermittent Onan Revisited [message #188347 is a reply to message #188273] |
Fri, 26 October 2012 14:14 |
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Robert Mueller wrote on Thu, 25 October 2012 18:38]Roy,
Stay tuned to this channel for next year's installment - we'll be heading to Arizona then north!
Regards,
Rob M
Back in the day I ran 2 of those Bendix pumps in parallel on my Olds powered ski boat. as they got older they pumped less and less gas especially when they warmed up but they kept on ticking making me think I had a different problem.
Roy Keen
Rob, if you don't stop and spend a few days with Roy and me, we'll have to consider you and enemy of the state!
geo groth '73 260 Sequoia
Carson City Nevada 89703
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| Re: [GMCnet] Intermittent Onan Revisited [message #188351 is a reply to message #188347] |
Fri, 26 October 2012 14:35 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Roy,
I'm hoping that's what I'll find when I replace the pump on Double Trouble, if not I wasted $92!
George,
I'd be happy to spend a couple of days with you and George telling lies about the GMC but I don't run the tour - I'm just the
mechanic and chauffer! ;-)
Regards,
Rob M.
-----Original Message-----
From: George Groth
Back in the day I ran 2 of those Bendix pumps in parallel on my Olds powered ski boat. as they got older they pumped less and less
gas especially when they warmed up but they kept on ticking making me think I had a different problem.
Roy Keen
Rob, if you don't stop and spend a few days with Roy and me, we'll have to consider you and enemy of the state!
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GMCnet mailing list
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Intermittent Onan Revisited [message #188363 is a reply to message #188357] |
Fri, 26 October 2012 15:54 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Dan,
I wouldn't bother even once we figger out the root cause:
1) vapor locking
2) vapor locking effecting old pumps
3) old pumps
You can wait until it begins to happen on your Onan then just call your buddy out in Newark. ;-)
Regards,
Rob M.
-----Original Message-----
From: Dan Gregg
Hmmm, I have a spare board and coil. Do I now need a spare fuel pump?
Dan
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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