Home » Public Forums » GMCnet » [GMCnet] Onan - Vapor Lock?
| [GMCnet] Onan - Vapor Lock? [message #178444] |
Mon, 30 July 2012 20:04  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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G’day,
It seems that whenever the OAT gets to the mid nineties the Onan plays up. When the gas is "cold" it runs just fine. As the day
heats up or if we drive with it on it starts to hunt and then finally shuts down. If I try to restart it immediately no joy but if I
let it sit for about 5 minutes I will start and run for a few minutes then it dies again.
When I was here in February I disassembled the carb and cleaned it thoroughly which must be true as when it's cool it runs PERFECTLY
with a voltage output of 120.
Last week before we left I removed the fuel pump and disassembled it. The "piston" moved up and down in the "bore" nicely, both
plastic check valve balls were in fine shape and moved easily.
I removed the solenoid at the inlet to the pump as I reckoned it was one thing less to fail.
I installed a Pertronics mod a couple of years ago and a new Onan coil.
I really think this is a vapor lock problem - it was 97° in Carlsberg, NM today,
Oh yeah, I did check the fuel level in both tanks and both above 1/2.
As they say in this neck of the woods - any idears?
Regards,
Rob M.
USAussie - Downunder
PS - SURE GLAD I INSTALLED A SECOND ROOF AIR LAST YEAR!
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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] Onan - Vapor Lock? [message #178451 is a reply to message #178444] |
Mon, 30 July 2012 20:35  |
armandminnie
Messages: 864
Registered: May 2009
Location: Marana, AZ
Karma: 2
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Rob, do you have a prime button for the Onan? If you do, it would be interesting to see if you could prime it and see if it starts immediately. You said if you rest it for 5 minutes and then start it will run for a little while? How long do you have to let it sit before it will start and stay running? Can you ever get it running again that day?
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
visit my gmc blog
click here to visit gmcws.org
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| Re: [GMCnet] Onan - Vapor Lock? [message #178454 is a reply to message #178444] |
Mon, 30 July 2012 20:42 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Rob,
You didn't mention your fuel lines. Although unlikely, could they deform when hot and expose a crack letting air into the fuel pump?
I just think it has to be before the electric pump, assuming the pump isn't tired or the voltage to the pump is low.
Also the hoses to the Onan get no love and they see more movement than other hoses.
Larry Davick
On Jul 30, 2012, at 6:04 PM, "Rob Mueller" <robmueller@iinet.net.au> wrote:
> G’day,
>
> It seems that whenever the OAT gets to the mid nineties the Onan plays up. When the gas is "cold" it runs just fine. As the day
> heats up or if we drive with it on it starts to hunt and then finally shuts down. If I try to restart it immediately no joy but if I
> let it sit for about 5 minutes I will start and run for a few minutes then it dies again.
>
> When I was here in February I disassembled the carb and cleaned it thoroughly which must be true as when it's cool it runs PERFECTLY
> with a voltage output of 120.
>
> Last week before we left I removed the fuel pump and disassembled it. The "piston" moved up and down in the "bore" nicely, both
> plastic check valve balls were in fine shape and moved easily.
>
> I removed the solenoid at the inlet to the pump as I reckoned it was one thing less to fail.
>
> I installed a Pertronics mod a couple of years ago and a new Onan coil.
>
> I really think this is a vapor lock problem - it was 97° in Carlsberg, NM today,
>
> Oh yeah, I did check the fuel level in both tanks and both above 1/2.
>
> As they say in this neck of the woods - any idears?
>
> Regards,
> Rob M.
> USAussie - Downunder
>
> PS - SURE GLAD I INSTALLED A SECOND ROOF AIR LAST YEAR!
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Onan - Vapor Lock? [message #178455 is a reply to message #178444] |
Mon, 30 July 2012 20:51 |
Dennis sch
Messages: 58
Registered: July 2012
Location: United States
Karma: 1
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Member |
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I had the same problem with mine. I did the same thing you did. then while I was on a road trip it let me down so I stop at a auto zone and picked up a universal fuel pump 3-7psi $50 i installed it in the parking lot 5 years ago and it solved my problems the gen runs like new every time we go. we just got back from a 10 day road trip and it ran every day at least 8hr a day the best 50 bucks I've spent
| Robert Mueller wrote on Mon, 30 July 2012 20:04 |
G’day,
It seems that whenever the OAT gets to the mid nineties the Onan plays up. When the gas is "cold" it runs just fine. As the day
heats up or if we drive with it on it starts to hunt and then finally shuts down. If I try to restart it immediately no joy but if I
let it sit for about 5 minutes I will start and run for a few minutes then it dies again.
When I was here in February I disassembled the carb and cleaned it thoroughly which must be true as when it's cool it runs PERFECTLY
with a voltage output of 120.
Last week before we left I removed the fuel pump and disassembled it. The "piston" moved up and down in the "bore" nicely, both
plastic check valve balls were in fine shape and moved easily.
I removed the solenoid at the inlet to the pump as I reckoned it was one thing less to fail.
I installed a Pertronics mod a couple of years ago and a new Onan coil.
I really think this is a vapor lock problem - it was 97° in Carlsberg, NM today,
Oh yeah, I did check the fuel level in both tanks and both above 1/2.
As they say in this neck of the woods - any idears?
Regards,
Rob M.
USAussie - Downunder
PS - SURE GLAD I INSTALLED A SECOND ROOF AIR LAST YEAR!
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Dennis S
Panama City FL
73 260
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| Re: [GMCnet] Onan - Vapor Lock? [message #178462 is a reply to message #178451] |
Mon, 30 July 2012 21:06 |
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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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Armand,
Good idea - multiple responses:
1) Yes, I have a prime button for the Onan
2) No it's not wired in yet
3) I will jumper No. 5 & No. 9 on the board and see what happens
4) Haven't timed how long I have to let it sit
5) Yes when it cools down it will start and run again
Regards,
Rob M.
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Armand Minnie
Sent: Monday, July 30, 2012 7:36 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Onan - Vapor Lock?
Rob, do you have a prime button for the Onan? If you do, it would be interesting to see if you could prime it and see if it starts
immediately. You said if you rest it for 5 minutes and then start it will run for a little while? How long do you have to let it sit
before it will start and stay running? Can you ever get it running again that day?
--
Armand
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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] Onan - Vapor Lock? [message #178472 is a reply to message #178444] |
Mon, 30 July 2012 21:49 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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Hi, Rob.
Somebody here said about two or three weeks back
that O'Reilly and maybe others have a blister pack
electric fuel pump that will work great for an Onan
for just under $50!
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
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*[ ]~~~[][ ][|\
*--OO--[]---O-*
> From: robmueller@iinet.net.au
> To: gmclist@temp.gmcnet.org
> Date: Mon, 30 Jul 2012 20:04:22 -0500
> Subject: [GMCnet] Onan - Vapor Lock?
>
> G’day,
>
> It seems that whenever the OAT gets to the mid nineties the Onan plays up. When the gas is "cold" it runs just fine. As the day
> heats up or if we drive with it on it starts to hunt and then finally shuts down. If I try to restart it immediately no joy but if I
> let it sit for about 5 minutes I will start and run for a few minutes then it dies again.
>
> When I was here in February I disassembled the carb and cleaned it thoroughly which must be true as when it's cool it runs PERFECTLY
> with a voltage output of 120.
>
> Last week before we left I removed the fuel pump and disassembled it. The "piston" moved up and down in the "bore" nicely, both
> plastic check valve balls were in fine shape and moved easily.
>
> I removed the solenoid at the inlet to the pump as I reckoned it was one thing less to fail.
>
> I installed a Pertronics mod a couple of years ago and a new Onan coil.
>
> I really think this is a vapor lock problem - it was 97° in Carlsberg, NM today,
>
> Oh yeah, I did check the fuel level in both tanks and both above 1/2.
>
> As they say in this neck of the woods - any idears?
>
> Regards,
> Rob M.
> USAussie - Downunder
>
> PS - SURE GLAD I INSTALLED A SECOND ROOF AIR LAST YEAR!
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| Re: [GMCnet] Onan - Vapor Lock? [message #178473 is a reply to message #178444] |
Mon, 30 July 2012 21:54 |
captjack
Messages: 271
Registered: February 2010
Location: Sebastopol, California
Karma: 1
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Senior Member |
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My experience is that when it's hot outside, first the Onan shuts down due to (it would appear) vapor lock. A short time later the coach has vapor lock. I've gone to intank fuel pumps for the coach, but not for the Onan. So far I don't have enough experience with the intanks to state that my vapor lock problems are a thing of the past.
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
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| Re: [GMCnet] Onan - Vapor Lock? [message #178484 is a reply to message #178455] |
Mon, 30 July 2012 22:54 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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| Dennis sch wrote on Mon, 30 July 2012 18:51 |
I had the same problem with mine. I did the same thing you did. then while I was on a road trip it let me down so I stop at a auto zone and picked up a universal fuel pump 3-7psi $50 i installed it in the parking lot 5 years ago and it solved my problems the gen runs like new every time we go. we just got back from a 10 day road trip and it ran every day at least 8hr a day the best 50 bucks I've spent
| Robert Mueller wrote on Mon, 30 July 2012 20:04 |
G’day,
It seems that whenever the OAT gets to the mid nineties the Onan plays up. When the gas is "cold" it runs just fine. As the day
heats up or if we drive with it on it starts to hunt and then finally shuts down. If I try to restart it immediately no joy but if I
let it sit for about 5 minutes I will start and run for a few minutes then it dies again.
When I was here in February I disassembled the carb and cleaned it thoroughly which must be true as when it's cool it runs PERFECTLY
with a voltage output of 120.
Last week before we left I removed the fuel pump and disassembled it. The "piston" moved up and down in the "bore" nicely, both
plastic check valve balls were in fine shape and moved easily.
I removed the solenoid at the inlet to the pump as I reckoned it was one thing less to fail.
I installed a Pertronics mod a couple of years ago and a new Onan coil.
I really think this is a vapor lock problem - it was 97° in Carlsberg, NM today,
Oh yeah, I did check the fuel level in both tanks and both above 1/2.
As they say in this neck of the woods - any idears?
Regards,
Rob M.
USAussie - Downunder
PS - SURE GLAD I INSTALLED A SECOND ROOF AIR LAST YEAR!
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Rob,
I have had the same sort of behavior out of my Onan on the last couple of trips. It would shut off, at first, after about an hour and a half, the about an hour, next time it went for about 30 minutes, next time, 15 minutes. I have done the same as you have, rebuilt/cleaned the carb, replaced all the fuel lines, "overhauled" the fuel pump, plus, I put in heavier oil, and a new LOP switch.
I have concluded, like Dennis (above), that the problem is the fuel pump. I have a new one, a Mr Gasket, from Jim K. in my garage, waiting to be installed. Unfortunately, I won't get a chance to use the coach until October sometime to test it. But, I am confident that the new pump will fix 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: [GMCnet] Onan - Vapor Lock? [message #178497 is a reply to message #178481] |
Mon, 30 July 2012 23:49 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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If it really is vapor lock, the only fixes I see is to quit buying that crapanol laced fuel or install and electric fuel pump at the tank and push the fuel rather than sucking it with the pump at the Onan. If you do install a pump at the tank be careful not to go too high in pressure. I believe I read somewhere that the Onan pump is only 3 PSI. That is from memory and I could be wrong. I would power that pump from the same source as the current Onan pump.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan - Vapor Lock? [message #178564 is a reply to message #178444] |
Tue, 31 July 2012 13:19 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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| Robert Mueller wrote on Mon, 30 July 2012 20:04 |
G’day,
<SNIP>
I removed the solenoid at the inlet to the pump as I reckoned it was one thing less to fail.
I installed a Pertronics mod a couple of years ago and a new Onan coil.
I really think this is a vapor lock problem - it was 97° in Carlsberg, NM today,
Oh yeah, I did check the fuel level in both tanks and both above 1/2.
As they say in this neck of the woods - any ideas?
Regards,
|
Re the solenoid valve: Someone (Dan?) had removed the Onan fuel shutoff solenoid valve and then had a problem when the fuel tank pressurized and overwhelmed the needle valve on the Onan. Therefore I plan on leaving mine installed.
Re Onan vapor lock problem: If I encounter this, or maybe before, I will mount the Onan fuel pump at the same level as the bottom of the tank. That way the only low pressure section of the Onan fuel supply system will be from the surface of the gas in the tank up to the top of the tank. Once the system is primed the pump inlet would even have a slight positive static pressure.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] Onan - Vapor Lock? [message #178602 is a reply to message #178589] |
Tue, 31 July 2012 22:19 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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| Robert Mueller wrote on Tue, 31 July 2012 19:30 |
Steve,
The solenoid has two wires going to it (+/-) they come over from the control board. It appeared to me that it is either on/open or
off/closed. I don't know of any device on the Onan that would cause it to regulate pressure or flow from the tank to the pump /
carb.
I vaguely remember reading that the solenoid was added because of some Canadian rule.
Rob M.
|
Correct - the solenoid valve has no pressure regulating function other than: Onan off = zero fuel flow. The example was that the GMC was parked with the Onan off. Fuel was spilling from the carb.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] Onan - Vapor Lock? [message #178606 is a reply to message #178602] |
Tue, 31 July 2012 22:42 |
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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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Steve,
See my last message under Onan replacement pump. It is supposed to have an anti-siphon function (positive shut off).
Having said that I do agree that at some point if there was enough pressure in the fuel tanks on a hot day it could drive fuel
through the pump and into the carb inlet and overcome the float valve.
Regards,
Rob M.
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Steve Southworth
Sent: Tuesday, July 31, 2012 9:19 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Onan - Vapor Lock?
Robert Mueller wrote on Tue, 31 July 2012 19:30
> Steve,
>
> The solenoid has two wires going to it (+/-) they come over from the control board. It appeared to me that it is either on/open or
> off/closed. I don't know of any device on the Onan that would cause it to regulate pressure or flow from the tank to the pump /
> carb.
>
> I vaguely remember reading that the solenoid was added because of some Canadian rule.
>
> Rob M.
Correct - the solenoid valve has no pressure regulating function other than: Onan off = zero fuel flow. The example was that the
GMC was parked with the Onan off. Fuel was spilling from the carb.
--
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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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