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Old 09-11-2011, 07:11 PM   #1
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Newmar Owners Club
Ford Super Duty Owner
Join Date: Sep 2011
Location: Overland Park, KS
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Question Onan 7.5 Gas won't run on hot days

I have recently purchased a 1996 Newmar Kountry Aire gas MH with an Onan Emerald 7.5 KW gen set. The Onan is located in the right front storage compartment, just to the right and just behind the Ford 460 engine. We have just had a very hot summer here in the midwest. If the temperature outside is over 100 degrees (F), when we need the roof air the most, and we are driving the coach, the Onan will run for about 20 minutes, then surge once or twice and then die. It will not restart until after the day and the coach have cooled down. Then it takes a LOT of cranking (I assume to refill the fuel lines) before it will start again. If you don't drive the coach, it does not fail, if the temperature is under 95 degrees, it does not fail. We have replaced the fuel pump, but that did not fix the problem. I have double checked and the summer/winter lever is on summer, and the altitude compensator is set correctly. I have traced the fuel line and I don't see where it is getting close to the engine or exhaust system. I am sure that I'm getting a heat-related vapor lock, but does anyone have any suggestions for corrective action?

Chuck in Kansas City
1996 Newmar Kountry Aire
38' class A Motor Home
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Old 09-11-2011, 07:27 PM   #2
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Maybe install a fuel pump back near the gas tank?

1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake
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Old 09-11-2011, 07:42 PM   #3
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Location: Surprise Arizona
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It is possible that it is shutting down due to inverter over temp. Try opening the inverter compartment. Also check that the inverter fan is running.
There is a part for Onans that can be installed to prevent vapor lock. Cant remember the part number but it is installed on the carbeurator.
Harold & Linda
2009 CT coachworks siena 35V
W22 Workhorse 8.1L. Explorer Sport toad,
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gas, onan

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