| Strange ONAN behavior [message #308441] |
Sat, 08 October 2016 20:07  |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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Had some strange ONAN behavior after the GMCMI convention. We were traveling and running the ONAN for the coach AC for a few hours. Stopped at camp Waimart and shut down the AC and the ONAN. About 10 minutes later THE BIRD (her royal highass queen Chloe the Goffin) announced she was way overdue for her dinner. When starting the ONAN for the microwave it was surging, missing, backfiring and hunting to the extent it was unuseable. This went on for 10 minutes or so before we gave up on it. After it cooled for several hours It ran just fine. Since then no other problems.
???? What was going on there? Any ideas?
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: Strange ONAN behavior [message #308446 is a reply to message #308441] |
Sat, 08 October 2016 22:17  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Winter mix gasoline.
The EPA Summer Blend requirement expired on Sept 15th so the refineries switched to fuel with a higher RVP number which means that the fuel evaporates at a lower temperature. It is also is cheaper to make.
I had a similar problem with Summer Blend fuel (plus ethanol) that I got in Missouri when going to the GMCMI Branson rally last June. The added Eehanol gives it a 1 point higher RVP number. At 102 F. my Onan quit with vapor lock. After cooling for about an hour it ran fine again for 20 minutes and then vapor locked again.
The problem with the Onan is the fuel pump sits just below the carb and has to suck the gas a long way out of the tank which makes vapor lock more likely.
What I have done to mine to try to prevent this in the future is to insulate the entire fuel pump with reflective Microfoil insulation. I also covered the fuel line with aviation fire sleeve insulation covered with reflective aluminum tape.
I have not had the problem again but I also have not driven at 102 F with the Onan running.
If you choose to do this DO Not USE BUBBLE WRAP FOIL (reflectix) as it is highly flammable. Use Microfoil from Northern Ohio Foam Products because it will not support combustion. If you call them and ask for samples, they will send you enough for free to cover the fuel pump.
http://www.nofp.com/insulation-products/microfoil
Another thing you can do is to move the fuel pump back to a point along side of the tank so It is not sucking fuel but instead is pushing the fuel through the heated area around the running Onan.
You can also help the situation by not buying ethanol diluted fuel whenever possible to get away from the 1.0 point RVP difference.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Strange ONAN behavior [message #308533 is a reply to message #308446] |
Mon, 10 October 2016 21:51 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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Ken I'll agree with you on the summer/winter gas thoughts. It makes sense and would explain the behaviors that I observed.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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