RV generator seems to always “run out of gas”

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gary-736Hi Doc,
Here’s a problem we just discovered. For years we’ve had trouble keeping our generator running. It just seemed to “run out of gas.” Our mechanic first installed a new gas line to the gas tank, then discovered that virtually no gas was coming out of the tube leading to the generator. He now proposes to lower the gas tank to look inside the tank to try and discover why it cannot suck any more gas out of the tank. What do you believe might be the problem? What suggestions do you have for fixing the problem? Thanks! —Joe P.

Hey Joe,
Most generators (should) tap into the fuel container from the top of the tank through what’s called a “take-off tube.” There is usually a short piece of rubber hose or tube attached to the lower portion of the take-off tube that extends down inside the container to about the 1/4-full position. This draw tube only extends to the 1/4-full mark so that the generator cannot run the motorhome out of fuel if you’re out in the forest somewhere.

It’s quite possible this hose extension or tube inside the tank has fallen off or become detached somehow. Some draw tubes may even include an in-tank filter of some type. In the shop, we drop the tank, remove the take-off tube and pull it out to check and make the repair if necessary.

Another explanation is that perhaps the hose has become disengaged from the top of the take-off tube, outside of but located above the tank. In some instances it is necessary to lower the tank just to check that out.


In yet another scenario, older fuel hoses have a tendency to develop tiny cracks due to age, heat and exposure to the elements. These small cracks may not leak fuel, but they can suck in air as the fuel pump on the generator tries to bring in fuel. It still might be necessary to drop the fuel tank in order to replace the hose all the way from the take-off tube to the generator, so I’m hoping your technician did replace the full length of the hose.

To verify the hose is connected to the take-off tube, I used to remove the hose at the generator and then shoot low pressure air backwards through the hose and into the fuel tank, and had someone listen for the air bubbles at the tank fill inlet. If air can get in, fuel should be able to get out.

And finally, it could be a faulty fuel pump on the generator. You could always run a short piece of hose from a gas can directly to the generator. If the generator runs fine at that point, you know the problem is in the fuel delivery system of the motorhome. If it still acts up, the problem is on the generator. This is usually the first step in the troubleshooting process. There could be a faulty check valve, electric solenoid or plugged fuel filter somewhere in the fuel delivery system between the tank and the generator. Once those components are eliminated as the cause, it just might be necessary to drop the tank, at least partially, to rectify the problem. 

Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.

##RVT843

 

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Phil Ehlinger
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Phil Ehlinger

We spent some uncomfortable time when our Onan 5.5 kw would run out of gas for no reason. Changing the fuel filter didn’t help. The discovered Onan generators older than 5 years have a history of this problem, which is solved by replacing the fuel pump, not expensive nor hard to do. We had this problem and discovered the “cure” online after several “expert servicepeople” were unable to solve the problem. Change the fuel filter while you’re at it.