Good Sam Club Open Roads Forum: Class A Motorhomes: Generator vapor locking
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 > Generator vapor locking

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dodge guy

Bartlett IL

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Posted: 07/19/20 10:08pm Link  |  Quote  |  Print  |  Notify Moderator

So I've been trying to track down this issue I have been having with my 5500 Cummings/Onan generator. It will die out intermittently. I finally tracked it down to it dies when you hit a very rough highway or harsh jolt from a dip on a bridge expansion joint. And I diagnosed it even further in that it does it only when hot outside 85+ degrees. I found that if you give the generator a good push/shake it will want to die or will die. It doesn't do it when it 85 or less. It has a complete tune up, filters, oil plugs etc. I'm going to clean the carb and maybe decaf in it. It has 370 hours on it. But it's not a runny no idling problem. I believe the gas in the carb is boiling and when it gets shaken hard it sucks the air from the boiling gas.
Has anyone run into this. I was going to install some type of vent on the outside generator door, but when I open the compartment it's not hot. When I open up the generator cover you can really feel the heat, which is why I'm think the fuel is boiling when it's hot outside. The generator will run with no issues when it's below 80, it never dies then!
I have an outdoor thermometer in one of my compartments for outside use. I have seen storage compartment temps over 110 degrees. My gen is at the LR so it's getting all the heat sucked into it instead of cooler air.

Anyone?


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pconroy328

Colorado

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Posted: 07/19/20 10:57pm Link  |  Quote  |  Print  |  Notify Moderator

I've got the 4K version and I think you've described what ours does to a "T".

Today it's upper 90's and the generator just shut it self off while we were sitting in a parking lot. I popped open the door and it's an oven in there. I've seen people cutting the door up and installing a DIY grill.

I'm thinking of doing that to try to help dissipate the heat.

Heisenberg

West Texas

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Posted: 07/19/20 11:39pm Link  |  Quote  |  Print  |  Notify Moderator

It was the altitude adjustment screw for me, the cooling on the 5500 is a closed system with directional air.


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Gjac

Milford, CT

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Posted: 07/20/20 07:19am Link  |  Quote  |  Print  |  Notify Moderator

I have heard of people putting a fan in that area to remove the heat and some would just open the door when stationary.

PastorCharlie

NC

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Posted: 07/20/20 07:55am Link  |  Quote  |  Print  |  Notify Moderator

On mine I replaced the fuel pump and solved all the problem.

Dale.Traveling

Newport News, VA

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Posted: 07/20/20 10:31am Link  |  Quote  |  Print  |  Notify Moderator

PastorCharlie wrote:

On mine I replaced the fuel pump and solved all the problem.


My first thought also. Gasoline will boil at 180 degrees but I think the fuel pump gets a bit wonkers first and shuts off.

I would hold off doing and owner mods to the shell of the generator. Cutting vents or such is a bit of a last resort option to me considering the difficulty to restore to original state. The 5500 is very common, has been around for a number of years and is designed to keep it's self cool with all the access panels in place. If there was a cooling issue it would show up in just about ever generator in use and wold be an endless thread on the various RV forums.


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dougrainer

Carrolton, Texas

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Posted: 07/20/20 11:40am Link  |  Quote  |  Print  |  Notify Moderator

Vapor lock on a correctly installed Onan will not happen. What you describe is classic BURPING of the Oil and causing momentary loss of pressure that the Oil pressure switch sees and kills the Genset.
1. Make sure Oil level is correct. OVER full will result in same problem as under full.
2. Make sure you are using the correct viscosity oil
3. Last, Oil Pressure switches are cheap($20). Replace it Doug

dodge guy

Bartlett IL

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Posted: 07/20/20 02:49pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks everyone. The only thing I was thinking was installing a vent in the outside door that accesses the Generator. I’ve seen some newer MH’s with a similar vent.

As far as the generator itself. I was thinking it was the oil level, but ruled that out on several occasions. I’ve tried full to the max mark when hot. Tried to max mark when cold. And slightly overfilled. Always does when it’s hot out and I got a very harsh dip or anything that shakes the MH hard. Yesterday coming home it ran fine for about 6 hours. Then one hard bridge expansion joint and it died. It always starts right back up. That’s why I’m thinking it’s not vapor locking. The fuel pump is a good idea. Maybe I’ll try that. It’s cheap considering. I may first try and unplug the oil switch and See if it still dies. It doesn’t use oil. So for 5-6 hours it will be fine. Like I said it only does on the road, never stationary.

PhilipB

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Posted: 07/20/20 03:09pm Link  |  Quote  |  Print  |  Notify Moderator

You might try putting a fan near it and seeing if that helps. I have the same generator in our toy hauler. Our's has a drop frame in front for more storage, so when level, the generator is fairly close to the ground. I had a shroud made (under side) that channels the exhaust side towards the driver side, leaving the fuel/air inlet side cooler.


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GPWayne

Lake Stevens. WA

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Posted: 07/20/20 04:59pm Link  |  Quote  |  Print  |  Notify Moderator

Check your cooling air outflow screen. I once found a mouse nest and family blocking 50% of the air flow. Not all that easy to clear. But no problem after that.

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