Generator vapor locking

[dodge_guy]

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?

[dodge_guy]

No I haven’t checked the fuel pressure. But since it is a low psi electric pump it’s max pressure will only be about 7 psi. So if it’s weak it will run slower. Not enough to die but not enough to keep the float bowl full. And yes it always starts right back up, but it needs to crank about 5-7 seconds before it starts. Like it has to fill the bowl. The oil I’m running is 20W50 IIRC. The RV is in storage right now. The 7 signs you listed are for vehicle engines, not a generator. I will watch the video. Thanks.

[Bruce_Brown]

dodge guy wrote:
It very well could be a fuel pump. If it were weak Pump) and electric pumps are known to work at slower speeds when they get hot) would Cause the issue I’m having. I can’t see it being an oil issue only at hotter temps. I will try the pump first. If not then I’ll do an oil switch. If it were an oil switch issue it should give a code on why it shut down. I never get a code. There is no code to be set for low fuel flow. So if it died due to low fuel it wouldn’t set a code.

It's your money so do what you want.

If it were my money I'd start with the oil switch as Doug suggested. Pretty cheap and easy to try, and 100% makes sense as to what is happening, as he explained.

With that said, we once owned a Ford powered MH that would die when it got hot - it was the fuel pump. The big difference is that one wouldn't immediately re-start and run well. Sometimes it would re-start and limp, sometimes it wouldn't re-start until it had cooled.

[dougrainer]

Watch this video. Doug
I am giving you 41 years working on Onan Gensets. I did NOT base my advice on this video. I found it looking up codes for the Genset.

https://www.youtube.com/watch?v=Zqu2U_PGgj8

[dougrainer]

dodge guy wrote:
It very well could be a fuel pump. If it were weak Pump) and electric pumps are known to work at slower speeds when they get hot) would Cause the issue I’m having. I can’t see it being an oil issue only at hotter temps. I will try the pump first. If not then I’ll do an oil switch. If it were an oil switch issue it should give a code on why it shut down. I never get a code. There is no code to be set for low fuel flow. So if it died due to low fuel it wouldn’t set a code.

OIL gets THINNER as it gets hot. You have not answered my questions but you seem willing to spend money. What Weight Oil is in the Genset? Does it start right back up after it kills? Doug

PS. NOTE that none of these state kill of engine.
Seven Fuel Pump Warning Signs
Engine Sputters at High Speeds. ...
Rising Temperature. ...
Fuel Pressure Gauge. ...
Loss of Power When the Vehicle Is Under Stress. ...
Surging. ...
Decreased Gas Mileage. ...
Engine Will Not Start.

[dodge_guy]

It very well could be a fuel pump. If it were weak Pump) and electric pumps are known to work at slower speeds when they get hot) would Cause the issue I’m having. I can’t see it being an oil issue only at hotter temps. I will try the pump first. If not then I’ll do an oil switch. If it were an oil switch issue it should give a code on why it shut down. I never get a code. There is no code to be set for low fuel flow. So if it died due to low fuel it wouldn’t set a code.

[dougrainer]

For those than think fuel pump------There is a set amount of fuel in the Carb fuel bowl. The Pump does NOT supply continous fuel to the carb. There is a Float with a needle jet. The bowl continues to fill and the Needle valve shuts off excess flow. So, if the fuel pump was the issue, that would NOT cause an instantainous killing of the Genset. If the fuel pump was bad , then the Genset would kill at anytime. A "BUMP" would, if anything, cause a Pump to start running not kill it. Also, OIL problem(Switch) and viscosity will yield the Genset starting right back up when it dies. DOES THE GENSET START RIGHT BACK UP AFTER IT DIES? If so, you problem is not fuel supply or Vapor lock. I still state to replace the Oil pressure switch. That is a LOT cheaper than a fuel pump. DO NOT, install a regular automotive similar fuel pump. Those run at a higher PSI than an Onan pump. Doug

[Lantley]

full-timer wrote:
A new fuel pump fixed the exact problem on mine also.

I like the fuel pump idea next I think it's just easier to bypass/eliminate the oil switch first.

[full-timer]

A new fuel pump fixed the exact problem on mine also.

[Lantley]

It seems Doug is on to something. If its heat related I would think it would do it while you are parked as well. I would assume the compartment would still heat up when parked and there is zero air flow.
More importantly it happens if you shove or shake it manually which is not heat related. I don't think you can shove the genset it into vapor lock?
It appears from Doug's post the oil switch is a known issue.

[GPWayne]

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.

[PhilipB]

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.

[dodge_guy]

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.

[dougrainer]

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

[Dale_Traveling]

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.

[PastorCharlie]

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