I parked my RV on a slant (forward down) and the next morning noticed a major leak from below the generator. I lost about 30 gallons of gas, before I finally put it in neutral and coasted it down the driveway to a more level spot. The leak continued. It seams as though once I lost enough gas from the main tank to the generator, the leak stopped (started with a full tank and now have 1/4). I looked on the back side of the generator to see if there was a cracked hose and the hose going into the generator looks good. Now I'm faced with opening the back of the generator to see what may be going on inside. It looks pretty tricky to unbolt the metal housing that the generator sits in, to get access to the back panel of the generator itself. Any help would be appreciated.2007 Forest River-SunSeeker 4000 Onan Generator

It seems virtually impossible for fuel to drain from the main tank via the generator fuel line. Generator is not (well shouldn't be and not in my experience) gravity fed. Shouldn't be possible to lose significant fuel out of the tank unless there's a hole in the tank itself. All the fuel pickups come out the top of the tank. Unelss a full line literally was cut and was able to pull a siphon until it emptied the tank.

Fuel leaking from a carburetor almost always means a colored needle valve or sunk float. Yes, the carburetor needs to be removed.

Whataday,WOW!!! THAT is a LOT of fuel to leak out. I'm not sure if your Onan 400 shares a similar design to our Onan Marquis Gold 7kWatt (also gas). I'm going back a number of years here, so hopefully my memory isn't too far off. I can tell you that originally my generator had two fuel filters: one right on the generator and another before the generator fuel pump. It was kind of strange, but that's the way they did it. Well, getting the fuel lines on the filter on the generator tight enough so they wouldn't leak was a bit of a trick. It was behind the air cleaner housing. If you completely removed the air cleaner housing assembly, you could generally get things tight enough. But if you tried to take a shortcut and not remove the air cleaner assembly, you couldn't get the connections tight enough and it would eventually vibrate loose and leak. I noticed mine leaking one time. This was a couple of weeks after I did the fuel filter change. It didn't leak immediately after I changed the filter. When I went to the local Onan parts distributor, he sold me a "new" filter kit. It only had the one filter that went down by the fuel pump and a little doodad (technical term) which permanently replaced the filter mounted on the generator. It was a short length of tube which had six sides (like a nut) so that it could easily be tightened with the air cleaner assembly in place. Apparently, the leaking was a very common problem, so they removed one of the filters from the system and replace it with this new part. Since this new "doodad" didn't have to be serviced, it minimized that leaking issue once it was installed properly. Here's a link which talks about the Onan gas fuel filters. Again, this was for the Onan Marquis Gold generators.Again, I have no idea if your 4000 series is similar, but if it is, perhaps that's the problem. Check to see if there is a filter mounted on the generator and if it's leaking fuel, or looks like the source of the leak. Perhaps your generator never got the update kit.Good Luck,~Rick

That is a very dangerous situation...take it very serious!The fuel like going to the generator I believe *IS* gravity fed. I believe this because when you change the fuel filter you have to pop off that fuel line and it immediately starts leaking gas and you need to plug it while you change the fuel filter.It stops leaking at 1/4 tank, because that's as low as your generator can draw gas from the main tank (BY DESIGN).If you are lucky, the fuel line is leaking at or before it gets to the fuel filter. That might be an easy fix. Do you see clamps of some sort where the fuel line connects to the fuel filter. If staring at the generator, the fuel line can be found outside the generator coming in from the left side.Do you see gas in the bottom tray of the generator?? If so, perhaps it is leaking from inside the cover somewhere.Since your generator wasn't running, it is a gravity fed issue and should be leaking somewhere before the fuel pump.-Chris

It sounds as though the fuel flowed until it got down to the bottom of your fuel pickup tube in the tank. If so there are several ways this can occur. It appears one of your readers has ruled out all possibilities which means it just didn't happen. I would add some fuel and level the rig. At that point turn everything off and see if it leaks. Also listen at the generator to hear if a pump or small motor is running.

Fuel leaking from within the generator | Good Sam Community

14 Replies

Grit_dog
Navigator
Aug 29, 2021
He musta ben trollin…..
Grit_dog
Navigator
Aug 28, 2021
Well for such a dire issue and ask for help, OP must have figured it out, since he ain’t been back!
SJ-Chris
Explorer II
Aug 28, 2021
I recently had my Onan 4000w generator rebuilt by an Onan generator EXPERT (...he rebuilds them and has done dozens or maybe hundreds...). Regarding the fuel pump, I was told to be careful regarding the fuel pump replacement. He said some non-OEM makers of these fuel pump replacements do NOT have an internal shutoff valve mechanism and can result in situations where fuel can leak (...leak until your tank is at 1/4 full, so it could be a lot).

Any idea if your fuel pump is an Onan fuel pump or an aftermarket fuel pump which might have this problem?

-Chris
zigzagrv
Explorer
Aug 28, 2021
sch911 wrote:
Gravity feed or not doesn't matter. When parked on a angle. If the carb float is sunk or needle and seat are stuck open the fuel can syphon right out of the tank. Open up the generator remove the carb and re build it. Or take it to someone who can.

^^^^^ THIS ^^^^^
jjrbus
Explorer
Aug 28, 2021
Restricted evaporator system for RV can allow pressure to build up in tank and force gasoline out any opening it can find. Possibly have 2 problems?? Remove gas cap from rv tank and see what happens.
sch911
Explorer
Aug 27, 2021
Gravity feed or not doesn't matter. When parked on a angle. If the carb float is sunk or needle and seat are stuck open the fuel can syphon right out of the tank. Open up the generator remove the carb and re build it. Or take it to someone who can.
SJ-Chris
Explorer II
Aug 27, 2021
Rick Jay wrote:

Please be careful as your troubleshoot this problem. Make sure all of the leaked gasoline is cleaned up before you try to start the generator.

Good Luck,

~Rick

I *strongly* recommend you have a fire extinguisher next to you while troubleshooting.

My impression is that most of these fuel lines from the gas tank are physically connected to the RV gas tank at the 1/4 level and therefore they will stop allowing gas to the generator anytime the tank dips below 1/4 full. Perhaps I'm wrong, but that's the way I've always understood it. (...and of course different RVs can be hooked up different ways)

Good luck!
Chris
Rick_Jay
Explorer II
Aug 27, 2021
I don't believe the fuel line is a gravity feed. I say this because I believe the pickup tube comes out the top of the gas tank. I know it does on my rig (Class A, so it might be different.)

That said, it IS a siphon issue. If there is gas in the line and you open the line (or a leak develops), the siphoning action will allow the gas to continue to flow until either the siphon is broken or the level of gas drops below the pickup tube. Which will also break the siphon action.

Please be careful as your troubleshoot this problem. Make sure all of the leaked gasoline is cleaned up before you try to start the generator.

Good Luck,

~Rick
Grit_dog
Navigator
Aug 27, 2021
I stand corrected, if the generator fuel line pickup is gravity out of the vehicle’s main tank.

But since you don’t believe my post bgum, tell us where the fuel is coming from then please.
bgum
Explorer
Aug 27, 2021
It sounds as though the fuel flowed until it got down to the bottom of your fuel pickup tube in the tank. If so there are several ways this can occur. It appears one of your readers has ruled out all possibilities which means it just didn't happen.
I would add some fuel and level the rig. At that point turn everything off and see if it leaks. Also listen at the generator to hear if a pump or small motor is running.