[Stevage]

After getting my tank professionally re-sealed and reinstalled, my right tank fuel gauge on my 1996-completed RV-4 reads off-scale high regardless of fuel level.

Prior to any attempted repairs, the tank was only barely weeping fuel from a few rivets, and I asked my A&P if he would attempt the Loctite 290 & vacuum repair method; however, this introduced 2 new leaks that prevented any use of the tank.

I was able to correct one of the leaks which had developed at the fuel sender. I solved this leak by tightening the base nut on the fuel sender; however, the bolt seemed to rotate with the nut a small amount until I was able to cinch the nut down tightly. This stopped the fuel leak at that location.

My concern is that perhaps I damaged something within the fuel sender, now that I am having the fuel gauge read off-scale high at all times. Can anyone let me know if they suspect this would be the case or if there is another likely cause after the complete re-sealing? Thanks for your help.

 

[rvbuilder2002]

After getting my tank professionally re-sealed and reinstalled, my right tank fuel gauge on my 1996-completed RV-4 reads off-scale high regardless of fuel level.

Prior to any attempted repairs, the tank was only barely weeping fuel from a few rivets, and I asked my A&P if he would attempt the Loctite 290 & vacuum repair method; however, this introduced 2 new leaks that prevented any use of the tank.

I was able to correct one of the leaks which had developed at the fuel sender. I solved this leak by tightening the base nut on the fuel sender; however, the bolt seemed to rotate with the nut a small amount until I was able to cinch the nut down tightly. This stopped the fuel leak at that location.

My concern is that perhaps I damaged something within the fuel sender, now that I am having the fuel gauge read off-scale high at all times. Can anyone let me know if they suspect this would be the case or if there is another likely cause after the complete re-sealing? Thanks for your help.

Since the standard fuel senders typically used on RV’s have no base nut, it is hard to say.
Can you post a photo of what you tightened?
The only nut is typically the one for the fuel pickup fitting.
If that is the one you turned, you could have rotated the fuel pickup in the tank and jammed the sender to full position ( this would also cause other issues that could lead to an engine failure).
Though if you did this before having someone repair the other leaks, they might have noticed (but you didn’t mention what procedure the used).

 

[Ralph Inkster]

Sounds like your wire terminal is grounding out. Is there a fiber washer under your wire ring terminal?

 

[Avanza]

After getting my tank professionally re-sealed and reinstalled, my right tank fuel gauge on my 1996-completed RV-4 reads off-scale high regardless of fuel level.

Prior to any attempted repairs, the tank was only barely weeping fuel from a few rivets, and I asked my A&P if he would attempt the Loctite 290 & vacuum repair method; however, this introduced 2 new leaks that prevented any use of the tank.

I was able to correct one of the leaks which had developed at the fuel sender. I solved this leak by tightening the base nut on the fuel sender; however, the bolt seemed to rotate with the nut a small amount until I was able to cinch the nut down tightly. This stopped the fuel leak at that location.

My concern is that perhaps I damaged something within the fuel sender, now that I am having the fuel gauge read off-scale high at all times. Can anyone let me know if they suspect this would be the case or if there is another likely cause after the complete re-sealing? Thanks for your help.

A fuel gauge is an important instrument. As I understand it, you are somewhat concerned about the fuel sender has been damaged.
If it where my plane, I would replace the fuel sender with a new one and closely follow the installation instructions.

Good luck

 

[Walt]

My $.02 ... FWIW -

If you have an early "float" type Rochester (or equivalent) fuel gage, the center (+) threaded "pin" is prevented from rotation simply by friction developed by the tightening (at the factory) of the outside nut, which is in contact with the Phenolic insulating washer & the solder joint of the wire coming from the "wiper" of the resistance element on the inside. IF (big if), the threaded pin is rotated when installing the ring terminal from the wiring harness, the possibility exists that the solder joint can be compromised - which can lead to an "open" circuit - ergo, infinite resistance, meaning your gage in the cockpit interprets the signal to mean full (all the time).

A shorted sender unit/wire will read full, an open will read empty.

 

[HFS]

A shorted sender unit/wire will read full, an open will read empty.

Thanks Walt - I knew I should have paid more attention in my EE classes ...

 

[Stevage]

Since the standard fuel senders typically used on RV’s have no base nut, it is hard to say.
Can you post a photo of what you tightened?
The only nut is typically the one for the fuel pickup fitting.
If that is the one you turned, you could have rotated the fuel pickup in the tank and jammed the sender to full position ( this would also cause other issues that could lead to an engine failure).
Though if you did this before having someone repair the other leaks, they might have noticed (but you didn’t mention what procedure the used).

Since the standard fuel senders typically used on RV’s have no base nut, it is hard to say.
Can you post a photo of what you tightened?
The only nut is typically the one for the fuel pickup fitting.
If that is the one you turned, you could have rotated the fuel pickup in the tank and jammed the sender to full position ( this would also cause other issues that could lead to an engine failure).
Though if you did this before having someone repair the other leaks, they might have noticed (but you didn’t mention what procedure the used).

Here is a photo. The base nut I'm referring to is next to the tank separated with a lock washer.

After getting my tank professionally re-sealed and reinstalled, my right tank fuel gauge on my 1996-completed RV-4 reads off-scale high regardless of fuel level.

Prior to any attempted repairs, the tank was only barely weeping fuel from a few rivets, and I asked my A&P if he would attempt the Loctite 290 & vacuum repair method; however, this introduced 2 new leaks that prevented any use of the tank.

I was able to correct one of the leaks which had developed at the fuel sender. I solved this leak by tightening the base nut on the fuel sender; however, the bolt seemed to rotate with the nut a small amount until I was able to cinch the nut down tightly. This stopped the fuel leak at that location.

My concern is that perhaps I damaged something within the fuel sender, now that I am having the fuel gauge read off-scale high at all times. Can anyone let me know if they suspect this would be the case or if there is another likely cause after the complete re-sealing? Thanks for your help.

The base nut I'm referring to is next to the tank, separated by a lock washer. This is what I tightened to stop the leak.

 

[Stevage]

Since the standard fuel senders typically used on RV’s have no base nut, it is hard to say.
Can you post a photo of what you tightened?
The only nut is typically the one for the fuel pickup fitting.
If that is the one you turned, you could have rotated the fuel pickup in the tank and jammed the sender to full position ( this would also cause other issues that could lead to an engine failure).
Though if you did this before having someone repair the other leaks, they might have noticed (but you didn’t mention what procedure the used).

Here is a picture of the base nut I was referring to. It has a lock washer between it and the fuel tank.

 

[Stevage]

Sounds like your wire terminal is grounding out. Is there a fiber washer under your wire ring terminal?

There is no fiber washer under the wire ring terminal. Please see the photo I attached to an earlier reply.

 

[Stevage]

There is no fiber washer under the wire ring terminal. Please see the photo I attached to an earlier reply.

To clarify, there is no fiber washer under terminal connection, but there is what I remember to be a cork washer under the lock washer.

 

[rvbuilder2002]

Here is a picture of the base nut I was referring to. It has a lock washer between it and the fuel tank.View attachment 64309

I have never seen a fuel level sensor like that used in an RV fuel tank, so I’m not sure what you should do to troubleshoot it.
The standard fuel gauge used in most aircraft that have resistive style senders operates with a resistance range of 30 ohms for full to 240 ohms for empty.
The movement of the float arm produces a variable resistance that sweeps between these two values.
So, with typical troubleshooting, if the fuel level is always indicating full, it means the resistance sensed by the sensor wire is 30 ohms or less, which can also be a short to ground as Walt mentioned.

I suggest removing the wire and see what your fuel level indicator reads. If it changes to reading empty, then that would indicate you have a typical resistive style sensor.
Then I would measure the resistance of the stud on the sensor to ground.
If everything is working correctly, it should be at least 30 ohms.
If it is, then, something has happened to make your fuel level sensor, stuck in the full position.
It is interesting that the stud for the wire terminal is smaller diameter than the stud that mounts the sensor.
They may be insulated from each other in someway, which would mean there needs to be an insulating washer at the bottom of the hardware stack up so that the hardware isn’t electrically, connecting the smaller stud to the larger stud.

 

[PaulvS]

I think Scott is right. There should probably be an insulating washer between the big stud and the washers on the small stud. Possibly that insulater was lost when the tank was re-fitted after sealing and now the sensor wire is shorted to ground via the large stud. (Assuming the large stud is metal and not some type of plastic.)